How To Read Star Charts

Long before smartphone apps, star charts were the things to use when navigating the sky, especially when trying to use key stars to find a deep sky object. Even today, it can get tricky, so it’s important to know why the charts are the way they are, and how they help you!

Start with the Basic Circle Maps of the Entire Sky

If you read astronomy books or magazines, chances are you will run into one of these maps. You can also find websites that make custom maps for you on the internet! These are general maps for the sky, and are meant to guide you in the right direction. Sometimes they show where the planets are if they are meant to be current maps, but don’t expect every map to be the same.

This is a star map for the winter night sky in the northern hemisphere. Many publications have maps for each month and a particular time, but this example map is best used for January at 9 pm.

To properly read it, you need to have the directions on the map match the cardinal directions in the sky.

One way is to hold the map over your head, and make sure the sector that says south is pointed south, north needs to point north and so on. Since this is at night, you’d be holding a flashlight, preferably a red one with your other hand.

If holding it above your head isn’t your thing, you can hold the map normally, but to read it properly, you still need to make sure the direction you are facing is on the bottom.

Detailed Constellation Maps Help, But Make Note of Their Position and Angle

When trying to find deep sky objects, many astronomy publications will have detailed constellation maps that not only give you a good idea on which stars are the brightest, but where you can find deep sky objects!

We are going to use Ursa Major as an example.

The brighter the star, the bigger the dot. Also remember that the brightest stars in each constellation, even those with common names, are cataloged from brightest to dimmest using Greek letters, and if you don’t understand, then this concept is explained more in this article.

As you can tell, there are quite a few Messier Objects in this constellation. Many of them can be found by simply “star hopping,” or using the bright stars of the constellation as a guide to help you find the object.

Say you want to go for M109, which is a beautiful spiral galaxy. Naturally that means you should point it towards Gamma (γ) Ursa Majoris (γ UMa), which is also known as Phecda and then search near it.

Except, Ursa Major is not always in that same orientation. Throughout the year and during the night, the orientation changes with Earth’s rotation.

The same applies for all constellations, especially those that are rising and setting. Taurus and Gemini appear sideways when they rise in the east, but when they are setting, they appear right side up. Andromeda is the opposite, she appears right side up in the east, but upside down when she’s in the west.

So before you star hop, make sure your map is the correct orientation for the constellation, otherwise when you try to move your telescope to the desired object, it won’t be there!

Most objects can be found using this method, but be patient, especially when looking for galaxies and globular clusters, as they may not contrast that well against the sky if there is too much light pollution or if your telescope doesn’t collect enough light.

But Most People Nowadays Use Apps on Their Phone!

Yes it’s true.

Great smart device apps give you augmented reality views of the sky, and you can literally point your phone to any sector in the sky, and the app will give you the information you need. It will show you the constellation, AND… they are oriented to how they appear in the sky at the time!

Besides having databases of plenty of interesting deep sky objects, they also can have good detailed charts on background stars, which saves the hassle of bringing your books.

As everything is on computers, star charts and observers handbooks on printed media are becoming obsolete. But never count them out, as they can still be handy on nights when all your powered devices aren’t working!

Using A Star Chart or App with a Telescope

The Moon, bright stars, the naked eye planets, and even a few of the brighter deep sky objects can simply be “eyeballed” using the main tube at low magnification or a finder scope to center the telescope on an object before being centered.

But most of the dimmer deep sky objects, asteroids, and comets, are better found using the star charts or apps.

As an example, let’s say you want to find planet Uranus. While Uranus does have a distinct cyan color and doesn’t twinkle, it still appears star-like and can be difficult to tell apart at low magnification through your finder scope. So you point your telescope in the general direction of where it’s located, but again, you aren’t sure you got it right.

Remember that in your telescope, all the stars will be points of light, not circular discs that charts display. The discs of different sizes are there to scale the brightness of the stars compared to each other, and some of them account for the color as well.

So you consult the star app, and in your close up view, you see which star is Uranus and which are other stars. But through the telescope, it shows something different.

That is because there is one thing that star charts and phone apps don’t account for….

Telescopes invert the image!

This is what makes things tricky! It takes some time getting used to, and if you’re using a Newtonian reflector, there’s no way around it! Remember, there is no up and down in space!

One simple solution is to turn your map upside down, and it should match how it looks in your telescope. Still using Uranus as an example, if the background stars and Uranus’ location match what you see in the telescope, then congratulations, you found Uranus, and zooming in on the right object will show the disc!

Now if the view still does not match how the map shows, then you’re still not in the right place. But, perhaps you can find where your scope is pointed at by carefully seeing what patterns the background stars are making (lines, shapes, etc), and then finding the familiar spot on the map. If you catch that, you can then get an idea how close you are to the target, and where you need to move the telescope.

Refractors and Shmidt-Cassegrain telescopes will give you a correct image if a diagonal is being used, but still backwards from left to right. If you REALLY want the image to be right side up, you can get what’s called an “Erect Image Prism diagonal;” they can correct the backwards image.