Amateur Astronomy
Everything I wish someone had told me when I got started
There is a lot of information out there on Amateur Astronomy… a whole lot. There’s so much that it’s hard to know where to start, so that is what we’re going to do here - show you one way to get started and where to find additional information. We’ll keep things in a logical order that build on each other and provide you with a good foundation to follow up on anything that catches your interest in this hugely broad hobby. We’ll also provide you with a list of things you might like to get interested in.
Amateur Astronomy can be very formal and technical: Expensive optics, GPS enabled robo-scopes, plate solving programs, imaging equipment with incredible resolution, and lists of unbelievably faint and obscure objects. One of the great things about the hobby is that you can be just as much an Amateur Astronomer as anybody else if all you have is an economical 80mm Achromatic refractor and a star-finder app on your phone.
All you really need is a clear night, a star chart, a blanket or comfy chaise, and maybe a pair of binoculars.
Here we are not going to cover astro-imaging, the nuclear chemistry of stars, the physics of black holes, or the complex math behind celestial mechanics. There are much better resources available for those kinds of details and we’ll include a few references for those too.
What we are going to do is give you a good introduction to what there is to see in the sky and equip you with the basic skills to locate and observe anything there is… within the limitations of your equipment, your eyes, and that particular night’s sky. :-)
You won’t find anything new here - everything here has been developed and published all over the place by professional and amateur astronomers over the past 200 years or more. What you will find here is one place to keep you focused and get you back on track when you wander off into the internet search weeds.
One more thing: Even the basics can cover a lot of information. Don’t be intimidated. Enjoying the sky does not require a mastering of all we’re going to present. You choose what works for you. Just get out there.
It’s best to look at these in order but if you’re already familiar with some of it, then jump in anywhere. There’s really no wrong way to learn all this… but we think this is a pretty good one. :-)
BTW - This is a work in progress. We’ll start with an outline and then provide the details as we go. If a topic you’re interested in is not yet filled in, please come back later and check.
Once we do get everything filled in we’ll still be modifying the content per your feedback and adding to or changing the references when we find something we like better. We’ll also be adding images from our Club members.
Let’s get started.
Fred Rains
Outreach Coordinator
Birmingham Astronomical Society of Alabama
Goals and Outline
Our Goals:
1. Show you some of the things you can see and give you an idea of what they’ll really look like.
2. Show you three ways to find things.
3. Help you understand the limitations of the sky, your eyes, and equipment.
4. Show where to go next.
Outline:
1. Start with Safety
2. The Planisphere
3. Things to See
4. Magazine and Internet Images vs an Eyepiece
6. How the Sky Changes Hourly, Daily, and Yearly
7. Constellations and Asterisms
10. The Meridian, Ecliptic, and Zenith
11. How to Read a Star Map Using Alt/Az or Polar Coordinates
12. FOV, Magnification, and More Star Hopping
13. Putting It All Together Using an Inclinometer
14. Putting It All Together With an Equatorial Mount
15. Tips On How To See Something Once You Find It
16. What's In The Sky Right Now?
(More coming soon)
1. Start with Safety
You should start every observing session with a consideration for safety. This is a very safe hobby - but there are a few things you need to keep in mind.
1. Tell someone where you’re going, when you’ll be back, and check in with them.
2. Secure items in your vehicle: You don’t want a 15 pound counterweight bouncing around if you have to swerve to avoid an animal
3. Don’t trip over equipment: Make sure power cords and external batteries are out of the way. A white observation chair is a really good idea. Make sure your truck’s tailgate is up or has a red light on it - walking into that in the dark will leave a mark.
4. Wind, cold, heat, and lightning: Check the weather and dress accordingly. If you are going to be observing from a higher altitude remember it gets 3 degrees colder for every 1000’ of elevation. The temperature in the desert can get very cold at night and very hot during the day.
If you can hear thunder you can get struck by lightning. You are about to get struck by lightning If you suddenly realize the hair on your arms is standing up and you smell ozone. Immediately get in a car or building or squat down and low as you can with your feet touching. Do not get under a tree!
Have plenty of water, coffee, and snacks. Take some sunglasses, sunscreen, and a floppy hat. Take a pop-up canopy if there’s no shade nearby
5. Are you awake enough to drive home? Take a nap!
6. Animals and bugs: Have mosquito spray - I like the picaridin based sprays. They will not harm optics or plastics like DEET will. Lemon eucalyptus based repellents get good ratings.
Be mindful of larger animals in your part of the country - in our region the only thing that may bother you are wild pigs. If they come around then get in your vehicle until they leave.
7. Most people are nice… most. A little paranoia protects you from a lot of dumb. Try to observe with friends.
8. Heavy equipment - make sure someone is there to help you, or take something smaller.
9. If you’re going to be doing solar observing during the day, be sure you understand, and everyone around you understands solar viewing safety and the permanent damage that the Sun will do to your eyes.
10. Have a basic first aid kit - a few bandages and ointments for cuts and bruises. A couple of aspirin is a good idea.
11. Communications - do you know where you are and could you tell someone how to find you?
12. Powering your equipment off of your car can lead to a dead battery.
13. Some places you go for observing can be pretty remote. Did you gas up or charge up?
14. Did you bring your phone? Is it charged? Do you have a charging cord for the car? Reception?
15. Be familiar with your surroundings: our Club’s dark-ish spot is located on top of a bluff and there is an honest-to-goodness 200 foot cliff about 40 yards away
2. How to use a Planisphere
The quickest way to get started is with a Planisphere. If you’re lucky enough to still have a nearby bookstore you can usually get one of these in the Science/Astronomy section. If not, you can get them on the internet here and here. If you can’t wait to get one, you can print out an excellent monthly star chart here that has all the information that the Planisphere has but is only good for one month. The Planisphere is good for any day of the year from now on. Pretty slick for technology that’s been around since the 17th century.
Naturally there are apps for your phones, tablets, and laptops. A good one that you can get for free is Stellarium. There are several others and you can search for “planetarium apps” to see some options.
A planisphere has an outer cardboard or plastic stationary section and a round inner section that can be rotated. The outer section is marked off with the days of the year and the inner section is marked with the time of day/night. You simply line up the time of day with the day of the year and you see the stars and constellations in the sky at that time. The planisphere will have North South East and West printed on the stationary section. Note that East and West appear to be reversed - not so. The planisphere is made to be viewed while looking up at the sky. If you hold it over your head and point it North, you will see that East and West are in their correct spots.
Using nothing more than a planisphere you can learn the names of the seasonal bright stars and begin to learn the different shapes of the constellations. The brighter stars are designated with larger dots on the planisphere and you can begin to learn the different “magnitudes” of brightness. The planisphere also shows an outline of the Milky Way and a line called the “ecliptic” where all the planets and the Moon will be found. We’ll talk more about the ecliptic later. You can also determine the rise and set times of the Sun for any day of the year and the rise and set times of any constellation during the year. Again - a lot of information from a simple device made up of two pieces of cardboard. A video showing you how to use a planisphere is found here. One other thing you’ll need is a red penlight or a regular flashlight covered with several layers of red cellophane held by a rubber band. You can also use brake light repair tape. You want your eyes to be dark adapted which means the pupils have opened up nice and wide. A bright white light will dilate your pupils again and it will be a few minutes before they open back up and you can see faint objects ( in my case it could take up to 30 minutes to open back up). The eyes are not as sensitive to red light that is just bright enough for you to
read the planisphere.
Taking the planisphere out on clear nights and getting familiar with how the sky moves, being able to locate and name the brighter stars and constellations, and learning the stories and legends passed down through the ages - this may be all you ever want to do and, by itself, would be well worth the effort. It will also give you a good head start on the rest of what we’re about to cover.
3. Some of the Things to See
Our solar system consists of a star ( our Sun). Planets and moons, a rocky asteroid belt, and an outer cloud of left-over frozen stuff from the Solar System’s creation revolve around the Sun.
Our Sun and Solar System are part of the Milky Way galaxy - an enormous rotating island whirlpool of millions of stars, star systems, gas, dust, rocks, and ice that is all gravitationally bound together. All of this is traveling through space along with other island universes, each one separated from the other by incredible distances. Distances at this scale are measured by the speed of light (3 X 10^10 Meters/Sec). E.g, it takes light 8 light minutes to travel from the Sun to Earth. The Milky Way is almost 100,000 light “years” wide. Our Solar System is located about 1/2 of the way out from the center of the Milky way. Our Milky Way and all the other galaxies make up the Universe. The best information available is that the Universe is approximately 14 billion years old.
A more detailed description can be found here.
The Planets
Our planet ( Earth) revolves around the Sun once every 365.25 days or so. As it is moving around the Sun it is also rotating once every 24 hours. When a particular location on the planet is facing the Sun it is daytime for that location and when it is facing away from the Sun it is night. During the night you can look out into space and away from the Sun and see the different classes of objects. The stars you see are primarily in our local neighborhood of the Milky Way - about 300 light years away from us. Our Solar System has 8 recognized planets - there used to be a ninth - Pluto - but the definition of planet was redefined and Pluto did not make the cut. The four “inner” planets are: Mercury, Venus, Earth, and Mars. They are closest to the Sun and are rocky. The four “outer” planets, Jupiter, Saturn, Uranus, and Neptune, are “gas giants”. Mercury, Venus, Mars, Jupiter, Saturn, and on a real clear night - Uranus, can be seen in the sky with the naked eye. They look like stars but they don’t “twinkle” and they move in relation to the stars around them. The word “planet” comes from a Greek word for “wanderer”.
More details can be found here.
The Moon
A moon is a natural object in space that orbits another natural object in space like a planet or large asteroid. They are also called satellites. Some planets, e.g. Jupiter, have multiple moons and in some cases you can observe their movement from hour to hour through a small telescope. Earth has only one moon. “The” Moon is the natural satellite that orbits Earth. You could spend the rest of your life just observing the Moon and its craters, rilles,
mountains, and shadows.
More details can be found here.
Stars come in different colors
Most people think all the stars in the night sky are white. If you look closely you’ll find that some are actually yellow, red, and so white that they look blue. This has to do with how hot the star is at its surface. The hotter it is, the whiter/bluer it is. The cooler it is, the more red/yellow it is. On a clear dark night you can see approximately 2,000 stars with just your eyes. Binoculars and telescopes show many many more.
More details about stars can be found here and here.
Multiple Stars and color contrasting Multiple Stars
Many stars - some say most - that look like a single point of light to us, are not singular but are actually two or more stars that are gravitationally bound to each other, and from our perspective, very very close to one another. There are a few stars that aren’t actually close to each other but just appear that way because of the way they line up. These are called “optical doubles”. If viewed through a telescope, some of these star systems can be “resolved” as individual stars. Some of these multiple star systems are made up of stars that vary in brightness and some also vary in color due to the variations in the star’s temperatures. Some of these contrasting colors are striking and beautiful. It’s also fun to see just how close some of these star systems can be and still be resolved by your telescope.
More information about multiple stars can be found here and here.
Star Clusters
An “open cluster” of stars contains a few dozen to a few hundred individual stars in a loosely formed and gravitationally bound group that can take on interesting shapes in a telescope (e.g., NGC 457 looks like ET the Extraterrestrial from the old movie.) A “globular cluster” can have a few hundred thousand stars that are compacted into a dense ball. These look like a spoonful of sugar in a telescope and can contain several different colorful stars. Globular clusters are some of the oldest objects in the Universe.
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More information on star clusters can be found here.
Nebulae
Enormous clouds of gas and dust occupy certain regions of galaxies and can form a “nebula”. The plural of nebula is “nebulae” (pronounced, “ neh’-byu-lee”). Sometimes these clouds can be illuminated by nearby stars. These are called “reflection nebulae’. In some cases the gas clouds will glow when they are “charged” by nearby stars - similar to how a flourescent light works. These are called “emission nebulae”. Some emission nebulae are small and spherical and are called “planetaries” because their tiny discs look like a planet. Sometimes the clouds of dust and gas will prevent you from seeing what is behind them and cause dark patches in space. These are called “dark nebulae”. Our Milky Way Galaxy has many such nebulae and some of them take on identifiable shapes like dumbbells, horseheads, the North American Continent, and tiny smoke rings. These can be seen with telescopes. When a nebula condenses due to gravitational attraction it can become so compact that nuclear fusion occurs and the result is a new star.
More information about nebulae can be found here.
Galaxies
We talked about Galaxies a little at the first of this section. They are huge with millions of stars and they are all separated by incredible distances, but at least one of the distant ones can be seen from a dark spot with just your unaided eyes.You’ll need a telescope or a pair of binoculars to see others.
Our own Milky Way can sometimes be seen if the night is clear and dark enough. You are looking edgewise through it and the millions of stars look like a glowing cloud that stretches all the way across the sky. If you look more closely at it through a telescope you can begin to see all those stars and other things that are discussed above. The center of our Milky Way is in the constellation of Sagittarius.
More information on galaxies can be found here.
4. Magazines and Internet Images vs an Eyepiece
Until I can get some of our wonderful club imagers to duplicate what you see in the eyepiece… there are sketches! As long as there has been a telescope there have been gifted individuals who make sketches of what they see in the eyepiece. And some of them are very good. These are very close if not exactly what you will see through the eyepiece. Great examples of this art can be found here. Compare them to some of the images of the same objects in the previous section, Some of the things to see.
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5. Which Way is North?
The majority of people in this world do not know which way is north. Don’t feel bad if you’re one of them - all of us have gotten too used to looking at glowing screens and listening to young ladies in our cell phones tell us where to turn.
Why is knowing where North is located so important? Because you will be using charts that reference North, South, East, and West and, although you can simply look at the stars, it sure is nice to know where to begin looking. North is also the zero point for a more specific reference system that shows you where to look a lot more accurately. We’ll cover that in a bit.
If it’s clear, the best way to find North is in the daytime. The Sun rises generally in the East and sets generally in the West. If you point your right arm toward the East and your left arm to the West you are then facing North and South is directly behind you. Pick a good landmark to the North you can reference at night. In some articles you’ll also find references such as North-North-East, Southwest,
etc. These are the points in between North, East, South, and West. There are 32 of these points and they define the “Compass Rose” used by ancient mariners to navigate the oceans. And they worked very well.
Today we use a magnetic compass that has 360 divisions called “degrees”. Looking North and moving 90 degrees clockwise along the horizon will take you to due-East. Continue moving 90 more degrees along the horizon and you are due-South. 90 more degrees and you are looking due-West. And 90 more degrees and you are back to where you started looking due North.
One thing you need to keep in mind is that a magnetic compass doesn’t always point to “true north”. The classic magnetic compass with its little red tipped arrow will point to “magnetic north” which can vary significantly from the true north you need for navigation using a geographic map. Because of the Earth’s magnetic field there is a “magnetic deviation” that must be taken into consideration if you are using a magnetic compass. This magnetic deviation is different for different locations on the planet and can be significant. To make it more interesting the local deviation itself changes slowly over the years as the Earth’s magnetic field evolves. You can learn more about magnetic deviation here. Also remember that the accuracy of a magnetic compass will be affected by nearby metal objects such as automobiles or even belt buckles.
Most cell phones have a built-in compass app that is usually very accurate. These apps will have the ability to switch between magnetic north and true north. Nearby metals objects will affect these apps also.
At night you have Polaris (Alpha Ursis Minoris) in the constellation of Ursa Minor, the Little Bear. Part of this constellation is called the Little Dipper and Polaris is the star at the tip of the Little Dipper’s handle. Polaris is the current “Pole Star”. This is a bright star that happens to be inline with the Earth’s rotational axis and points to “true north”. It appears to be stationary during the night as the other stars rotate around it in a counter-clockwise motion. The exact point in space that lines up with the Earth’s rotational axis and can be seen from the Northern Hemisphere is called the “North Celestial Pole”, or NCP. Currently Polaris is very close to the NCP. If you extend your arm and hold your hand out, the distance between Polaris and the NCP is less than the width of the finger nail on your little finger. The NCP actually moves very slowly through the sky from century to century. It will actually be closer to Polaris by the year 2100. A good article on finding Polaris is found here. There is corresponding South Celestial Pole, SCP, that can be seen from the Southern Hemisphere but there is currently no bright star nearby. Go here to see how to find the SCP. The movement of the two Celestial Poles is known by the intimidating name “Precession of the Equinoxes” - which basically describes how the Earth wobbles. More information on this can be found here.
6. How the Sky Changes Hourly, Daily, and Yearly
Yes, it’s the planet that’s rotating and revolving, but it’s handy to think of the sky doing the moving. The Sun rises in the general direction of the East in the morning and sets in the general direction of the West in the evening. More about the “general” part in a minute.
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Our Solar System is like a very thin, giant disc with the Sun at the center and the planets at different distances away from the center. From your high school geometry class, the disk is called a plane. This plane is called the “Plane of the Ecliptic”, or simply “The Ecliptic”. There is no real definition of “above” and “below” the Ecliptic so, for our discussion, we’ll call “above” the side of the Ecliptic that contains the North Celestial Pole, NCP, we talked about earlier. And “below” will be the other side of the Ecliptic. If you were to look down at the Solar System from above the Solar system you would see the Sun at the center and the planets revolving in a counterclockwise motion around it. This is why the stars appear to move a little farther to the West each night from our perspective here on Earth. If you saw a particular star straight overhead at 10PM local time, that same star would be a little farther to the West the next night at 10PM. And in about three months that same star would be setting at 10PM. And six more months after that, that same star would be rising in the East at 10PM. And three months after that it would be back straight overhead at 10PM exactly one year after you first observed it. All of this is due to the Earth orbiting the Sun. Every 12 months or so the Earth returns to the same spot in it’s orbit and that night you can see the stars that are away from us in that particular area of the Milky Way. Each night over the course of a year you can see all the stars that surround our Solar System in the Milky Way. Most of these stars are relatively close, around 300 light years away - some closer some farther. It’s estimated you can see 6000 stars with just your eyes over the course of the year. More information on all of this is found here.
The moon appears to move a little farther to the East each day. If you were looking down at the Earth’s north pole from out in space, you would see the moon revolving around the earth in a counterclockwise orbit. It takes 27 days and 8 hours for the Moon to make a complete orbit around the Earth. Occasionally the Moon’s orbit takes it directly between the Earth and Sun and you have a Solar Eclipse. Occasionally the Moon’s orbit takes it into the shadow of the Earth and you have a Lunar eclipse. Except during a Lunar eclipse, one side of the Moon is always fully illuminated by the Sun, but depending on where the moon is in its orbit, we see only a portion of the illuminated side. These are called the moon’s phases. A crescent moon we see only a sliver just before sunset or sunrise, a gibbous moon is a little more than half illuminated, a full moon is fully illuminated, and a new moon is not illuminated at all. For additional details you can look here.
We mentioned that the Sun rises “generally” in the East and sets “generally” in the west. We say generally because the Sun rises due East and sets due West only twice a year due the Earth’s axis being slightly tilted in relation to its orbit around the Sun. The other times the spot where the Sun rises is slowly moving North or South on the horizon. The sunrise reaches its northernmost point at the Summer Solstice, usually June 21st, and this is when the longest day of the year occurs in the Northern Hemisphere. ( This is also the Winter Solstice in the Southern Hemisphere) On this date in the Northern Hemisphere the Sun rises and sets then starts a slow movement to the South. It passes due East at the Autumn Equinox. The length of the days and nights are very nearly equal at an Equinox. The Sun continues south until it reaches the Winter Solstice, around December 21st. This is the shortest day and longest night in the Northern Hemisphere.
It then starts northward again and the cycle repeats. This is hard to get your head around at first… and at second. For now hit the “I believe” button and go here to get additional info.
7. Constellations and asterisms
A constellation is a group of stars in an area of the sky that has a pattern that reminds you of an object or animal or person. The origins of some constellations go back thousands of years and include Ursa Major ( The Big Bear), Ursa Minor ( The Little Bear), Hercules the Hero, Orion the Hunter, and Aquarius the Water Bearer.
The International Astronomical Union was organized in 1919 to, among other things, create a common set of naming guidelines and to establish a forum for issues within the worldwide Astronomical community. Part of the initial efforts included standardized boundaries for today’s 88 recognized constellations. You will see faint outlines on star maps that define the area in the sky, from our perspective here on Earth, associated with a particular constellation. This gives the amateur astronomer a starting point for finding things, kind of like knowing what State a City is in. Many times the recognizable features that make up a constellation are outlined on star maps. Some examples are shown here. As you gain time under the stars you’ll become familiar with these patterns and find it a lot easier to quickly locate things. More info can be found here.
An asterism is a grouping of stars that is part of a constellation or multiple constellations and has another identifiable shape and name. Examples of this include: The Big Dipper (The Plough in Great Britain) in Ursa Major, The Little Dipper in Ursa Minor, The Summer Triangle which consists of three bright stars from three different constellations, The Keystone in Hercules, The Northern Cross in Cygnus, The Teapot in Sagittarius, the great square in Pegasus, The Big W in Cassiopeia), and The Coathanger in Vulpecula. More about asterisms can be found here.
8. What Time / Day Is It?
First let’s discuss 12 hour time vs 24 hour time. Most clocks (digital and analog) will show the time displayed in hours from 1 to 12. You use the same hours for both night and day and refer to them as “AM” or “PM”. AM means “before mid-day” and PM means “after mid-day”. After 12 midnight it becomes 12AM and a new day begins. The hours between 12 midnight and 12 noon are called AM. After 12 Noon it becomes 12PM and the hours stay PM until 12 Midnight and it starts all over again.
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To avoid the AM and PM considerations some clocks simply use a 24 hour system. 1AM is called just “1” and 1PM is now called 13. 2PM is called 14, all the way to midnight which is 24 (its also 0 for the next day…). With a 24 hour format clock, any hour from 1 to 12 is before noon and any hour from 12 to 24 is after noon. See this site for an illustration. If you know the time in 24 hour format but you're more comfortable thinking in AM and PM, just subtract 12 from any hour between 12 and 24 to get the time in PM in a 12 hour format. Again - much easier to do than to explain. E.g. 20:00, sometimes called “twenty hundred hours” would be 20 -12 = 8PM on a 12 hour clock.
We are all familiar with our local time. The one quoted on the local news channels and shown on the signs outside banks and schools.
If you have traveled across the country you have run across “time zones” and had to move your clocks an hour or so one way or the other. Most of our cell phones these days do this automatically for us. A standardized time system across the world is a relatively recent thing. Before the late 19th Century each town and city had its own local time. This was based on the 24 hour day but it was centered around local noon. When you went from city to city you needed to find a local clock tower to know how to set your watch. In the early 1880’s it was decided that the world would be split into 24 time zones divided by lines of longitude. This was based on the movement of the Sun by 15 degrees every hour. Greenwich, England was chosen as the starting point and it was designated as the Prime Meridian. As the time zones move eastward from the Prime Meridian the clocks are moved ahead by one hour because a location to the east would see a sunrise more or less one hour before a location 15 degrees to the west. Your local time would be referenced to one of these time zones, such as 12 Noon CST for 12 noon Central Standard Time. Central Standard Time is 6 hours behind Greenwich time ( or “Greenwich Mean Time”). Greenwich Mean Time is also known as simply GMT and sometimes “Coordinated Universal Time”, or sometimes “Zulu” in the military. Universal Time, or simply UT. UT is the time listed in many astronomical lists so anyone anywhere can derive their own local time by knowing how many hours ahead or behind of UT their time zone is. This does get a little more complicated when you introduce Daylight Savings Time. This is the time of year when many, but not all, locals move the clocks ahead one hour on the same day to maximize the use of the daylight.
All these time zones do create a problem: if you could head east and travel around the world in one hour and when you started it was 12 noon on the first of the month at Greenwich and as you travel eastward you advance your clock one hour for each time zone, when you get back to Greenwich it would be 1:00 PM but you have added a whole calendar day. This was solved by “The International Date Line”. This is a line running roughly north and south 180 degrees from Greenwich. If you cross this line going from West to East you subtract one day. Going East to West you add one day. This convention keeps the calendar straight for travelers. The line is not according to International Law and it zig zags around according to some political boundaries. There is a Nautical International Date Line that is set by International Treaty and is used by the militaries of the world. More information can be found here.
Leap Years and Leap Seconds have to do with the fact that the Earth revolves around the Sun in 365.24 days and not 365 days like our calendars show. If we didn’t have Leap Years where we add an extra day (usually - there’s always a “usually”) in February, the calendars would slowly get out of synch with the seasons. A Leap Second is something similar but used to keep very accurate clocks in synch. You can read more about all this here and here.
Julian dates have a starting point in the distant past and are continuously counted from that starting point. They are in a format that is easily used in calculations and are at the heart of much of your goto astronomical equipment.
In general Epochs are very large periods of time during which something significant has occurred. Usually when an amateur astronomer refers to an epoch we are referring to the date when the location of astronomical objects were made. You’ll read more about that in the section on Equatorial Mounts and Polar Coordinates. These coordinates change very slowly and are updated every 50 years. We are currently in epoch J2000. Some older reference books that I have use epoch J1950 and are still plenty accurate enough for finding objects.
Sidereal Time refers to where the Earth is in its orbit around the Sun. We talked about this in the section on how the sky appears to move. If you know your sidereal time you can determine what objects will be available for viewing that evening. Refer here for more info.
A pretty good summary of all this is given here
9. Azimuth and Altitude
Azimuth is a measurement along the horizon. It divides the horizon into 360 “degrees”. True North is 0 degrees in Azimuth and it increases as you turn to the East until you make a full 360 degree circle and return to North. East is at 90 degrees, South is at 180 degrees, West is at 270 degrees, and back to the North at 0 degrees (which is the same as 360 degrees).
Altitude is also measured in degrees. The horizon is always at 0 degrees in altitude regardless of which direction you are looking. Straight up is 90 degrees from the horizon and If you continue straight back to the horizon behind you, you will have gone 180 degrees. Using Azimuth and Altitude you can find any location in the sky as we’ll go over shortly. A more detailed explanation of Azimuth and Altitude is found here.
An explanation of RA is found here. And here.
If you really want to get into the weeds look into International Celestial Reference Frame, or ICRF
10. The Meridian, Ecliptic, and Zenith
These are three locations in the sky that you need to get familiar with and you’ll use a lot.
The Meridian is a line in altitude that goes up from due North on the horizon, travels directly overhead to the South, and down to due South on the horizon.
The Zenith is the point directly above you in the sky.
The Ecliptic is a line where you’ll find the planets and the moon will not be too far off from it. From the Northern Hemisphere the Ecliptic is found running East to West on the South side of your zenith. In the Southern Hemisphere this line will be on the northern side of your Zenith. If you see a bright object on the Ecliptic that isn’t on your star chart… it’s a planet. More info is shown here.
11. How To Read a Star Map Using Alt/Az or Polar Coordinates
There are three basic maps: the planisphere, paper maps, and planetarium software.
We’ve already discussed one of them: the planisphere, where you have two pieces of either cardboard or plastic connected so that one of the pieces rotates within the other. The outer piece has a cutout that represents the sky. The inner piece has a star map and there are markings for the 24 hours in a day on this piece. The outer piece has markings for the days of the year . You can rotate the inner section until the time of day and day of the year line up and what you have in the cut out are the stars and constellations in the sky on that day and at that time. In effect you have an analog computer - pretty slick for something that has been around since the seventeenth century. You hold the planisphere so that the compass direction shown on the outer section points down and agrees with the direction you are facing. What you see on the planisphere are the stars and constellations above the horizon in that direction. The stars are represented by different sized dots - the larger the dot, the brighter the star. Again, this is 600 year old technology and it is still one of the best ways to discover the sky… It’s also a lot easier to do than to explain. See here for a video.
You can also print out basic monthly star maps here. These are very useful in learning your way around.
The planisphere and monthly star maps are great introductions to star hoping.
We discussed earlier how you can use Altitude and Azimuth to locate any object in the sky IF you have a planetarium app that gives you that information for the specific day and time of day you are observing. These numbers constantly change as the sky appears to rotate overhead. The Planisphere we just discussed can be adjusted accordingly to show you relative locations but a paper map needs another coordinate system that remains constant - this is where Polar Coordinates comes in. With alt/az coordinates you turn to a certain point on the horizon and then go straight up by a specific angle to locate an object; to use “polar coordinates” imagine that Polaris is the center of a bullseye with concentric circles extending outward and all the way to the south. These concentric circles show an object’s declination, or the angular distance in degrees from polaris. The circle extending outward from the Earth’s equator is 0 degrees and increases to 90 degrees at Polaris. It decreases southward to -90 degrees at the southern pole. Each degree, north and south, is made up of 60 arcminutes, and each minute is made up of 60 arcseconds. You add the “arc” to show you’re measuring an angle instead of time. This measurement is called Declination, or Dec. Every object in the sky has its own Dec. Now imagine there are lines extending out of Polaris like the spokes of a wheel. There are 24 of these spokes labeled from 0 to 24. If you’re facing polaris the spokes will increase , 0,1,2,3, etc., clockwise. The zero point for these 24 lines passes through the constellation of Pisces - although it’s called the First Point of Aries. Confused? It’s better with illustrations like the ones shown here. The spokes are measured in hours - and it’s no coincidence that this is just like the 24 hours in a day. Each hour is divided into 60 minutes, each minute into 60 seconds. This measurement is called Right Ascension, or RA. In this instance you’re really talking about minutes and seconds of time but before we get too far in the weeds lets only talk about the minutes and seconds of angle. See here for a good explanation of where Right Ascension came from.
Every object in the sky has its own RA. You follow that line until it crosses the object’s Dec to find the object. With these two coordinates, right ascension and declination, you can locate any object in the sky and, unlike an objects alt/az coordinates that change every minute, polar coordinates don’t change ( they actually do but its so slow the locations are seldom( every 50 years or so) updated. Polar Coordinates provide a convenient way to make maps of the sky. One of these that I particularly like is the Orion DeepMap 600. This is a folding map that shows the entire sky. It shows the RA as you move left or right, and it shows the DEC as you move up or down the map. It also has a listing of 600 popular objects on the back. This list shows an object’s RA and DEC and it’s easy to use these to find the object on the map and see where it lies in relation to the rest of the sky. Similar to the planisphere, you will have to turn the map one way or the other to get it lined up with how the sky looks at the time. Easy to do. Polar Coordinates also give you a way to construct an “equatorial mount” for your telescope. We’ll go more into detail on that in the “Put it all together” section.
There are also several atlas format books that show separate and more detailed maps for individual sections of the sky. These are also conveniently laid out in RA and DEC. You can search on “sky atlas” to find several options available. One of the more popular ones is the Pocket Sky Atlas.
This brings us to the planetarium apps for computers and cell phones. These can be incredibly powerful and provide an amazing amount of information. Some of these can be linked to the sensors in your tablet or phone and will show you what’s in the sky by simply pointing your device at the sky. Nice. They can zoom in and out and can show the Alt/Az coordinates or the Polar coordinates. Some can be connected to the more advanced telescopes and actually control the scope. Some of these can have a confusing learning curve but are well worth the effort. And a few are free downloads. Simply search for “planetarium apps” for more info. Two of my favorites are SkySafari and Stellarium.
You can also print out specific constellations, shown with RA and DEC coordinate grid, right off the internet here
12. FOV, Magnification, and More Star Hopping
We need to quickly touch on a couple of things and we can begin to put all this together.
There is a common malady called “Aperture Fever” where an amateur astronomer buys bigger and bigger telescopes in the hopes to see more and more. “Seeing more” means seeing fainter and fainter objects and also seeing smaller and smaller objects and finer and finer details on all objects. In general this is true and the larger the aperture (size of the objective lense or primary mirror) of a telescope, the more you can “see”. But there are some practical limitations to what you can expect to “see” and these are primarily due to the sky itself. We’ll discuss this more in the section on “How to Rate the Sky” but for now it is rare that the turbulence in the atmosphere will let you see anything at greater than 300 times magnification, 300X - regardless of the size of the scope. As a matter of fact it is an excellent night when you can observe at 300X. Most nights about 200X is the most you’re going to get. Above that the image will be brighter in a larger telescope but the image will degrade and get fuzzy with lack of detail. Be wary if you see an advertisement for a particular telescope that promises incredible magnifications above 300X.
There is a very good rule of thumb that says the maximum magnification to expect from a telescope is 50X to 60X the diameter in inches of a telescope’s objective lense or primary mirror. Always add to that, “up to 300X on great nights”. The good news is that, for most objects, the max magnification you’ll need is 150X.
To calculate the magnification of a telescope you divide its focal length by the focal length of the eyepiece. The focal length is the distance from the objective lense or the primary mirror to where an image is formed. The focal length of an eyepiece is the same thing and will always be much shorter than the focal length of the telescope.
Example: you have a 6 inch Newtonian Telescope ( a reflector) with a focal length of 1250mm (48”). You are using a 25mm focal length eyepiece. 1250/25 = 50X
Besides magnification you need to know the Field of View (FOV). This is the measure of “how much” sky you see when looking through an eyepiece. FOV is measured in degrees/arcminutes/arcseconds like the measures for the Altitude and Azimuth. (Remember that when minutes and seconds are used to measure angles they are technically called arcminutes and arcseconds to distinguish them from time - but folks usually leave out the “arc”. An eyepiece that yields a low magnification will show you the most FOV. The higher the magnification, the smaller the FOV. A typical FOV for a low magnification eyepiece is one degree (10). They can go much higher than that and they can go lower than that but for many telescopes the one degree max FOV is a good working number.
The 25mm eyepiece in the example above has a FOV of 1 degree. To visualize this you can extend your arm in front of you and hold up your hand to where you can see the finger nail on your little finger. That fingernail has an area of approximately 1 degree. A full moon has an area of 1/2 degree.
We’ll go over this in more detail in the calculations section.
( NOTE: you don’t need any math to enjoy the sky but a basic understanding of these concepts really helps)
Finally we get to “Star Hoping”. To star hop you use a paper map or planetarium app and locate the object you’d like to observe. You find a bright, easy to locate star near the object and, in our example above, you would imagine a one degree FOV and you see how many FOV’s you’d have to move the telescope to get to the object you’re looking for. There is a real good explanation and illustration of this here.
13. Putting It All Together Using an Inclinometer
An inclinometer (angle finder) is a device that measures angles. You can find these in the small tool section of the nearby big box hardware store usually near the bubble levels and tape measures. There are mechanical ones like this and there are digital ones like this. You can use one of these along with your planetarium app to easily find things in the sky.
Your planetarium app will give you an object’s location in RA/DEC and also in Alt/Az. First, be sure your telescope mount is level, this is important to assure that when you move the telescope in altitude that it goes straight up from the horizon. Then, using a star chart, point your telescope in the general direction of the object you’re looking for. Get the object’s altitude from the planetarium app, place the inclinometer on the scope optical tube, move the scope to the correct altitude, and pan left and right until you find the object.
Use an eyepiece with a FOV of at least one degree - the wider eyepiece FOV, the better. Also, remember that the object is moving (relative to us🙂) - update the altitude number for the object every couple of minutes if needed.
14. Putting It All Together With an Equatorial Mount
There are two basic equatorial mounts: the german equatorial and the fork equatorial. For simplicity we’ll discuss the german mount. The same principles apply to both.
There are some really nice german equatorial mounts with incredibly precise engraved setting circles, 10k step encoders, and carefully machined internal gearing. Most have digitally controlled drives with unfaltering goto capabilities, even in windy conditions… we will not be using one of those for illustration... We will use the EQ1 in the discussions. Even though the EQ1 is a very basic piece of equipment (read that cheap), and even though its setting circles are difficult to read, and even though its tolerances are such that it wobbles in a gentle breeze, it still provides the basic functionality of the most expensive equatorial mounts on the market. It will find anything the other mounts will, but instead of dead center, sub-arcsecond positioning of an object in your eyepiece, the EQ1 will get you within a couple of FOVs - good enough. And you don’t have to wait on a GPS to sync up or master complex handsets or know the exact date, time, and location to use the EQ1 - all you need are the polar coordinates of a visible star and the coordinates of the objects for the night. And if you can understand and use an EQ1 you won’t have any trouble with the rest of the mounts.
The EQ1
The EQ1 consists of a tripod and a mount that has a main axis that can be adjusted in altitude to point to Polaris. A telescope is attached such that it can rotate around the main axis in RA and it can also swing outward from Polaris in DEC. There are RA and DEC setting circles inscribed on the mount. Here’s the instruction manual.
1. If using a reflector you first check the collimation - this shouldn’t be needed for a refractor. Collimation can be done in the daylight and is not as hard to do as some folks would have you believe. You can use a laser, cheshire, or a simple collimation cap. I have an Orion StarBlast 4.5 on my EQ1 and I get good results with the collimation cap. More information on collimation of reflectors can be found here.
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2. Align your finder with your telescope. This can also be done during the day. Find an object a few blocks away and get it in your telescope eyepiece field of view. Cell towers, street lights, etc. work well for this. Adjust your finder until it is centered on the object. Turn the telescope to another object using the finder and check to be sure the object is also in the telescope eyepiece field of view. You’re done.
3. Polar align the mount.
This is a good time to go here and get familiar with the EQ1 controls shown in fig. 1 of the Orion Instruction Manual.
Roughly level the mount - for this method it doesn’t have to be perfectly level. We will go over another method below where it does need to be as level as possible but close-enough works for this one . Turn the telescope in Dec until Dec setting circle is at 900 and tighten the Dec lock screw. With many telescopes the Dec is permanently set at the factory and can not be changed. This is great. Then loosen the RA lock and position the telescope so the counterweight shaft is pointing straight down. Then tighten the RA lock screw. Again, close-enough to straight down works. Then, using the mount’s azimuth adjustment and latitude adjustments only, place the Polaris in the center of the telescope eyepiece. Tighten the altitude and azimuth locks. ( Sometimes these adjustments will move slightly when you tighten the alt and az lock screws - you may need to readjust to allow for this.) The mount is now polar aligned.
We’re lucky because the North Celestial Pole (NCP) happens to be very close to Polaris here in the Northern Hemisphere at this time in history ( See this article on Precession of the Equinoxes - basically the North Star changes every 3000 years or so because the Earth
wobbles).
Read this article on the Kochab method for a more accurate positioning of Polaris in the eyepiece - for a basic mount like the EQ1, getting Polaris in the center of the eyepiece works. (NOTE: This process assumes you have a clear view of Polaris at night. There are other ways of doing this in the daytime or if your view of Polaris is obstructed or if you are in the Southern Hemisphere. We’ll go over one of them at the end and provide references for others.)
4. Now, look up the RA and DEC of a bright star visible that night, then loosen the RA and DEC lock screws and point the telescope at that bright star ( closer to the Celestial Equator, the better - This would be a star with a DEC near 0 degrees). Once the star is in the center of the telescope’s eyepiece, adjust the mount’s RA setting circles to match the star’s RA. Check the DEC setting circle to verify it is in agreement with the star’s DEC. One thing I do is after I get the RA and DEC of the star I’ve chosen, I go ahead and move the scope in DEC to the star’s DEC. Then all you have to do is swing the telescope in RA to the star. You most likely will have to make a small adjustment with the Slow Motion controls but it saves a little time. You’re now good to go. To move to another object select its polar coordinates and move the mount to those coordinates. First remember that if you’re using a mount that does not have a motor to keep the RA moving as the sky moves, that you’ll need to simply be sure the RA setting circle is reset to the current target before moving to the next one. Again, the DEC setting circle does not move and is good. Do this each time before you move to the next target.
A good article on this is from the BBC Sky at Night website. The following images from an EQ1 mount can be found there.
This is a good spot to talk about “resolution” and “close enough”. Resolution is the realistic accuracy of the setting circles and close enough tells you how accurate you need to be with your numbers.
The first image is of the EQ1 DEC setting circle.
The larger tic marks are each 10 degrees, the smaller tic marks are each 5 degrees, and if you look closely there are also tiny tick marks that are each 2.5 degrees. To further complicate things, the metal index mark points too low and is too wide - bottom line is the best you can hope for is to get within 2.5 degrees of arc resolution using this DEC setting circle above.
The RA setting circle is shown below:
Here the larger tic marks are each 30 minutes and the smaller tic marks are each 10 minutes. The metal index mark is better positioned here and with a little practice you could split the 10 minute tic marks and get a 5 minute resolution. 5 minutes RA is about 1 degree of arc if you’re on the Celestial Equator ( hit the “I believe” button again.)
OK. Bottom line - If your EQ1 is perfectly polar aligned and you are using an eyepiece with a 1 degree FOV you would be able to get within a couple of FOVs in RA and within 3 or 4 FOVs in DEC by using the setting circles. In other words you’ll need to move around a bit but you will be “close enough” to the object you’re looking for.
If you get the RA/DEC of an object within 2.5 degrees in DEC and within 5 min of RA you are “close enough” to find your object with some panning around.
This is really not bad for a mount you can pick up for a$100 or less on the used market.
I have an Orion StarBlast 4.5 that I use on my EQ1. I get a little over 30 FOV and it doesn’t take much panning to find what I’m looking for.
More expensive mounts can be very accurately aligned, have larger setting circles, and in some cases verniers. Some of them are motor driven and some are pushto or goto. The EQ1 provides the same basic functionality as any of them and is a lot of fun to take to the field… every now and then.
All of this is much easier to do than to explain!
The last thing is the dreaded Meridian Flip… and it should not be dreaded. And again, it’s much easier to do than to explain.
If you’re looking at an object that is close to the zenith and on the East side of the Meridian you may find that the telescope may bump against the tripod legs or the mount itself and prevent you from moving to the object as it moves to the other side of the Meridian. Not a problem. Perform a Meridian Flip. If the RA of your object is 12 Hours or higher you need to subtract 12 and move the scope in RA to that new location. All this does is move the telescope 180 degrees from its original position. Since its polar aligned this means the object will still be parallel to the mount.( hit the “I believe” button till you get a chance to do this) If the RA of the new object is 12 hours of less you’ll need to add 12 hours to the object’s RA and move the scope to that new location. In both cases, you’ll need to swing the scope in DEC to the general direction of the new objects and then adjust the scope to the objects DEC. The DEC setting circles go from 0 degrees to 90 degrees back to 0 degrees back to 90 degrees and then back to the same 0 degrees you started with. When you point the scope in DEC to the general direction of the new object it puts you in the right section of the DEC setting circles. Simply fine tune the DEC to the objects DEC - no math involved.
Again, many DEC setting circles are set at the factory and do not move. It can get bumped and if you’re having a hard time finding things it could be because the 90 degree mark has moved. This will cause you to align the entire mount several degrees away from Polaris - not good. See the separate article on “Is the Mount Square?” that tells you how to check the 900 DEC position on your mount. Another possible problem is called Cone Error. All this means is that your telescope optical tube is not parallel to the mount’s main axis. This will make it point a little high or low and your alignment will be off. This is easy to check and fix and will also be covered in the “Is the Mount Square?” article.
Other things to keep straight with an equatorial mount:
1. You will have to loosen the OTA from time to time and rotate it to put the eyepiece in a better position. This does not hurt the alignment.
2. Be sure to use the correct set of RA numbers. There will be two sets of numbers on the RA setting circle: one for the Northern Hemisphere and one for the Southern Hemisphere. One of the first things you do after getting polar aligned is to stand behind the telescope, face North, move the scope clockwise in RA, and see which set of numbers is increasing as the mount rotates to the East. Those are the setting circle numbers you’ll be using.(You use the other set of numbers in the Southern Hemisphere.) It is REAL easy to use the wrong set of numbers.
3. Be sure the RA setting circles do not move when you move the scope from object to object. The EQ1 uses a thick grease to hold it and as the mount gets older the RA setting circle can slip and lose the RA alignment. Simply focus on a star of known RA and reset the setting circle. Pricier mounts will not have this problem.
4. The slow motion controls on the EQ-1 have limited travel and you’ll need to “center” them up from time to time. Again, this is not an issue with the more expensive mounts.
5. Can you see the Dec setting circles? If they are not on front of the mount facing the direction the OTA is looking then you have put the OTA on backwards -turn it around facing the other way…
6. Get familiar with where the RA and Dec locks are so you can find them in the dark.
Try an equatorial mount and see what you think…
15. Tips On How To See Something Once You Find It
Sooner or later you will utter the words, “ I don’t see anything!” Well, you may be in the wrong spot or your equipment may not be up to the task on that particular night or it could be that the object is in the center of the field of view and you haven’t learned how to see really faint objects. This is a very real skill you develop as you get experience observing.
There are a few age-old tricks of the trade you can try before you move to the next object. They include:
1. Use a red light. We mentioned this earlier. A white light will close up the eye’s pupil and a red light will allow it to open up and see fainter details.
2. Get a comfortable observing chair - this is the single best thing you can do.
3. Take your time - many times people will look into an eyepiece for 5 seconds and move on. Wait a little while longer and let your brain work on the image.
4. Move your eye slowly from side to side and up and down. This uses your “averted vision”. If you look a little to one side your eye is more sensitive to dim objects.
5. Tap the scope - this slight movement can reveal subtle changes.
6. Cover your head with a dark hood - this eliminates any background light around you that may be reflecting off the eyepiece. A dark towel at your feet can help if it’s really bright.
7. Change the magnification - this can darken or brighten the background and may improve contrast.
8. Smoking, alcohol, and altitude above 10K feet all have adverse effects on your eyes.
9. Wait for the object to get higher.
10. Try O3, UHC, or other filters
Get used to trying the above simple techniques and the next thing you say may be, “Ah, there it is.” There are other things as well but the above will get you started.
16. What's In The Night Sky Right Now
At every star party I eventually hear someone say, “What do I look at next?” You can start with a list. These lists will usually include the constellation the object is in and also the object’s polar coordinates in RA and DEC. A star chart will show you the locations for star hopping, and the planetarium apps will give you the current alt and az for the object.
There are two lists that I like in particular. One is provided by the River Bend Astronomy Club in Southern Illinois. The list is actually a combination of several popular lists and can be found here. The other list is the “All Splendours, No Fuzzies” that was put together by the Royal Astronomical Society of Canada. (“splendors is spelled “splendours” in Canada🙂) The Canadian list includes objects in the Southern Hemisphere that will not be seen from our Northern latitudes. The Messier and Caldwell catalogs are very popular. And there are observing programs by different organizations; the most popular being the ones of the Astronomical League. These lists are also not limited to the Northern Hemisphere and you can even get a decorative pin when you complete a program. There are lists of objects you can see with just your eyes if the sky conditions are good. There are lists of things to see with Binoculars. There are lists of things to see with telescopes of all sizes. There’s all kinds of lists that have been put together by professional and amateur astronomers over the years and you’ll probably come up with your own list of favorites.
There are also websites that point out interesting highlights of the current sky. These include Space.com, What’s up in Tonight’s Sky, and This Week’s Sky at a Glance. An internet search for “what’s up tonight” will show you many more.
Get a list of objects before you go out and have a plan.
You’ll see much much more.
17. Is The Mount Square?
Many of the more expensive equatorial mounts have a polar scope that actually fits inside the main RA axis of the mount and greatly facilitates lining up the main axis with the North or South Celestial Pole. The less expensive mounts - like the EQ1 - do not have this and you must use the telescope itself to polar align as we described earlier. The telescope must be parallel to the main axis in altitude and azimuth in order for an equatorial mount to point to where you want it to. More than likely the mount you are using was lined up well enough at the factory that you don’t need to be concerned about this. If not, depending on how out these two alignments are, finding things will be almost impossible.Luckily this is easy to check and doesn’t take long to do so. This is called checking for “cone error”. It’s also called “orthogonality correction” if you want to impress your friends.
First you check to see if the telescope is pointing high or low relative to the main axis. A good explanation of this is found here. And how to check for it and correct it if needed is also found in these videos here and here. This is easy to check and you can save A LOT of time.
It is rare that the DEC setting circle needs calibrating. These are set at the factory and in many cases there is no way to make any adjustments ( as is the EQ1). The more expensive german mounts will have small grub screws that can be loosened. (This is easy to do with a fork mounted scope as seen on p. 28 here.) For the german mounts you can verify that the telescope DEC setting circle 90 degree setting is correct. If this is off then the telescope is pointing a little to the left or right away from the main axis and when you see Polaris in the eyepiece the main axis will not be pointing to the Celestial Pole.
Balance the mount itself first. Then lower the main RA axis until it is level. Next move the scope in DEC until the counterweight arm is pointing straight down according to a level. Check the DEC setting circle setting and it should read 90 degrees. If it doesn’t and your mount’s DEC setting circle is non-adjustable, make a note of the actual setting and use that as your 90 degree point in the future. You’ll need to add or subtract this difference to the DEC readings for objects you are locating. If your mount has an adjustable DEC setting circle you can correct it at this time.