Identify Constellations

This session is to help you learn to identify bright stars and constellations in the night sky. These resources may be useful in the lab, or for later study.

For your laptop, home computer, cell phone, or tablet there are many choices.

Beautiful Stellarium is free planetarium software for Windows, Mac, or Linux operating systems and online in a browser. It is also available as a paid application for Android handheld devices.

The free Google Sky Map for Android works well, and makes use of Android device's navigation to interact with your real sky.

iTunes also offers a Sky Map for iPhone and iPad for a fee.

If want to pursue this and learn the night sky well, old technology works great. Consider getting a planisphere star finder, a rotating map of the sky that will show you how it appears on any date and time.

This lab will use Stellarium to help you learn to identify some of the prominent constellations and bright stars. If you have a Planisphere or one of the other applications on your handheld device or laptop, use it too.

Getting Started

First, there are a few things you need to know about using Stellarium. You might look at the Stellarium Tour on their website for an overview and reference to these options:

Screen mode

Stellarium starts in full screen mode and will cover everything. You can change this by pressing the F11 key to fit it into a smaller window.

Menu bars

There are two bars of menus, one at the bottom of the screen, and one on the left. They are hidden until you run the mouse down to the bottom or over to the left.

Quitting

When you or done, you can use the bottom menu bar to exit by selecting the off button.

Setting your location

By default you will be in Paris, France. If you press F6 the location menu will pop up and you can select your city or put in longitude and latitude. Once you have done this and saved the configuration, Stellarium will come up at your chosen site. The location menu is also in the left menubar under the compass icon at the top left. When you have selected your location the menu will show a map of Earth with an arrow pointing to your site.

Setting the time

Stellarium starts with the sky over your site at this very moment. The date and time will show at the lower right, based on the computer's clock. This time is the local time at your computer. If you change your location, the time shown will still be the time at your computer, not the time at the new site. For example, if you are in Baltimore, Maryland and you set up Stellarium for that site, then the computer is in the Eastern U.S. time zone. When you run Stellarium at 3 PM it will show the afternoon daytime sky with the Sun. Should you use the location menu to change to Rome, Italy, the sky will go dark because it's nighttime there. The clock will still show 3 PM because that's the time where you are. You can change the date and time in two ways. One is with the time menu selected from the left menu bar Clock icon. The other is with the two arrow icons at the right of the bottom menu bar. These speed forward-reverse, real time rate, and now buttons let you speed up the daily motions of the sky, and then slow them down again when you have the events in view you want to see.

Looking around

Change the direction you are looking by holding down the left mouse button and dragging your direction of view, or by using the updown leftright arrow keys on the keyboard.

Identifying planets, stars, and constellations

The lower menu offers options to add labels. By default the planets will be named, and you can turn this off using the Planets labels icon that looks like Saturn. You can outline the bright stars of the constellations, add constellation names, and even overlay mythological figures to help you see the patterns by clicking on the various buttons in this menu. There are two celestial grids offered too that show the equatorial celestial coordinates of stars (right ascension and declination), and the local sky coordinates (altitude and azimuth). A menu on the left for

Sky and viewing options

allows you to change the constellations, names and associated cultural folklore. Click that option, select

Starlore and Western

to see the the typical sky labels of American and European culture, or change to one of the others offered to see the diversity of named patterns in the sky. The same menu under

Markings

lets you select whether you would also like to see the constellation boundaries as red dotted lines. Sometimes it's helpful to see these in order to identify the constellation in which a particular object is located.

Identifying an object

Move the mouse over the object and click with the left button to have its identification displayed. Click with the right button to make this go away. Click with the center button (press down on the mouse wheel) to have the display center on this object after you have selected it.

Zooming in and out

The Page Up and Page Down keys on the keyboard zoom in and out of the sky. You can move around the zoomed in sky with the arrow keys or dragging with the left mouse button. The status display at the bottom of the view tells you the field of view

FOV

in degrees among other things. For some objects there is a photo that appears when the sky view is zoomed in close. When an object is selected and centered in the view, after zooming in the view will stay centered on it even as the day progresses. Think of it as a telescope that is pointing at your target, and tracking the target as the Earth rotates.

Finding Planets

The Moon and planets will be labeled by default. You can turn these names off with the P or by clicking on the Planet icon on the lower menu bar. If you select a planet with a left mouse click, the sky view will lockto that planet and you can follow it during the night. Planets with satellites like Jupiter will show the satellites as they really would appear in a telescope, and in motion in their orbits around the planet.

You can find a planet or other objects by using the

Search window

The left menu has a Magnifying glass icon that brings up this option. So does F3.

Finding Stars and Constellations

Stellarium starts with the sky as it is now, and you may run the clock forward or set the time for about an hour after sunset to see the night sky for the current season. In this lab study we will go through the seasons in sequence for the northern and the southern hemisphere, and help you find your way around the sky. The goal is to learn a few bright stars and constellations, seen from any place on Earth, and at any time of year.

It's daunting task, and the patterns will at first seem confusing. We'll help you find the brightest stars, and some recognizable patterns. The key to learning this skill is to become accustomed to the patterns so that your mind's eye will recognize them, even in a sky filled with stars you do not know.At the bottom of this unit there is are lists of constellations and bright stars that are the most among the most recognizable for each each in both southern and northern hemispheres.

In another lab experiment we will focus on the sky tonight, and on the planets. This one is more general and explores the stars and constellations seen from different locations on Earth. You should set Stellarium to see the sky tonight in your own locatin to begin with, and we will advise on changing this as we go along.

Bright Stars

Winter begins in late December for the northern hemisphere, or late June for the southern hemisphere. You can consult the list of stars and constellations at the bottom of this unit to see what should be visible then. Let's set set the time to 7 P.M. on January 15, when the sky is dark and stars are clear and bright. If you are in the northern hemisphere make sure your location is set properly, turn your attention toward the southeast and look for the brightest stars. (If you are in the southern hemisphere, for the following pick a favorite spot a little north of the equator so that you can see stars you are familiar with, as well as the stars of the northern sky.)

Sirius, the brightest star in the sky will be rising at this time. Left click on it and you'll see information about it displayed:

Names: Sirius (alpha Canis Majoris) HIP 32349

Sirius is its common name. Alpha Canis Majoris means that it is the brightest star in Canis Major, the big dog. HIP 32349 means that it is the 32,349th star of the Hipparcos catalog.

Magnitude: -1.45 (B-V: 0.00)

That's how bright it is on the astronomer's scale. Smaller numbers are brightest, larger ones fainter. Magnitude 6.0 is about as a faint a star as you can see without a telescope.

The magnitude scale is logarithmic, and a difference of 5 on this scale corresponds to a factor of 100x in energy received each second from the star. The B-V is a measure of color, and the 0.0 for Sirius means that it looks white to the eye. A positive number is red, and a negative number is blue.

Distance: 8.60 light years

Sirius is 8.6 light years from the Sun. The light you see in the sky from Sirius tonight left it 8.6 years ago, when you were 8.6 years younger. Light leaving the star today will arrive in 8.6 years when you are 8.6 years older.

Find these other stars: Procyon, Rigel, Betelgeuse and Aldebaran. For each one, identify what constellation is it in, and how bright it is.

1. What constellation are Rigel and Betelgeuse in?

2. What colors are these two stars?

Let time go by and watch the stars move across the sky.

3. Which of the stars Sirius, Procyon, Rigel, or Belegeuse is the one that gets highest in your sky during the night?

Notice the pattern of bright stars. These are the one's you'll see first in an urban sky.

Advance the date to March 5 and set the time again to about 2 hours after sunset.

4. Where are Sirius, Procyon, Rigel, Betelgeuse and Aldebaran in the sky now, compared to where they were at the same time in January?

Advance the date again to June 15 and now you'll see Deneb, Vega, and Altair rising in the east. Arcturus will be nearly overhead if you are in a northern latitude. During the night the stars will move across the sky

5. About what time on June 15 will Vega be overhead?

6. What is the name of another bright star in the same constellation that Deneb is in?

7. Which one of these stars, Arcturus, Deneb, Vega, or Altair, is orange? That is, which one is a cool star of type K or M?

Go forward again to the fall, and set the date to September 15. Look directly overhead if you are at northern latitude. If you are elsewhere, to answer this question set your location to a northern latitude of around 40 degrees. Three of the stars that you have identified form a distinctive pattern overhead called the Summer Triangle.

8. What are the three stars that define the "Summer Triangle" that is overhead in northern latitudes in late summer?

Constellations

Turn off the equatorial grid if you still have it on, and turn on the constellation names and outlines (use the lower menu or press C and V). Let's find some of the easily identified constellations in the northern sky for each season.

Set the date for January 15 at 10 P.M.

Orion with very bright stars Betelgeuse and Rigel are in the sky at this time.

Set the date for March 15 at 10 P.M.

Gemini, the twins , with the pair of similar stars Castor and Pollux comes in to view.

Set the date for June 15 at 10 P.M.

Leo, the lion, with the bright star Regulus is visible.

Set the date for September 15 at 10 P.M.

You will see Sagittarius, the archer, that looks like a teapot.

Set the date for November 15 at 10 P.M.

9. Where is Pegasus, the horse, at this time?

Stellarium lets you look at fainter stars, clusters of stars, nebulae, and galaxies too. See if you can find Messier 15 (M15) in Pegasus. It is a globular star cluster about 12 billion years old containing more than 100,000 stars. M15 is about 33,000 light years away, much farther than the nearby stars that define the constellations in the night sky.

10. There is a bright star in Pegasus quite close to M15 in the sky (but not in space). What is the name of that star, and how far from us is it? (Hint: Right click to get information on an object. This star is slightly red.)

Looking from the South

The following is a guided tour of the sky from the southern hemisphere to see how the sky would change if we moved our point of view to a southern latitude. From the north pole of the Earth you can see only the half of the sky that is north of the Earth's equator. Your horizon is the celestial equator. More of the southern sky becomes visible as you move southward. From the Earth's equator, the north pole of the sky is on the northern horizon and the south pole is on the southern horizon. Over 24 hours the entire sky will pass into and out of view.

Imagine now going south from your current location. The farther south you go, the more of the southern sky will be overhead. Let's illustrate this.

Set the date for January 15 at 10 PM by using the date and time menu "F5". Direct your view to the south and bring up the location menu with "F6". Use the map of Earth and click on a location that's south of yours, looking for a place that is at the same latitude and about 30 to 40 degrees below the equator. The sky will update each time you click a new location on Earth. Once you have a suitable location you can close the location menu.

Look for a familiar constellation that you have already identified from the northern location nearly overhead now.

There is a very bright star Canopus, south of Sirius, that you could not see from a northern location in the constellation of Carina.

11. What is the magnitude of Canopus? Which is brighter, Sirius or Canopus? (Hint: Right click in Stellarium to see the more about the object. The larger the magnitude, the fainter the star. Your unaided eye can see 6th magnitude.)

The bright star Achernar is not far away, a little southwest of the star you found in the question above. Set the field of view so that you can see a field of 70 to 90 degrees with Achernar on right. (If you're lost, try using the search option and type in the name to have the software center up on the object.)

There are two fuzzy clouds in the center of the field of view now. These are the Large and Small Magellanic Clouds, companion galaxies to our own Milky Way. If you need help in identifying them, the search term "SMC" in Stellarium will center the Small Magellanic Cloud.

12. What constellation is the SMC in?

Zoom in and you'll find an object that is not a star, and is close to the "SMC". Use the search term "47 Tuc" to center on it.

47 Tucanae (47 Tuc) is a giant globular star cluster. There's information about it in Stellarium, click here for a link to

Wikipedia, and you can also Google the term and find out more.

13. Which is farther away from us, the cluster 47 Tuc or the small SMC galaxy? (Hint: Search the web for information about both of these.)

Set the date and time to June 15. If you have chosen a location about 30 to 40 degrees south of the equator from your own longitude, then the time at this site will be the same as your local time. Try 10 PM to get the sky a couple of hours after sunset.

High in this southern hemisphere sky you will now see a distinctive pattern of bright stars that outlines the "Southern Cross". It will be above the south celestial pole, while the Magellanic Clouds at this time will be below the pole.

You can identify this pattern easily with the constellation outlines (C) and names (V) on. Look for "Crux".

14. Find the names of two bright stars in Crux.

Just east of Crux at this time of night is the constellation Centaurus. Look for the bright star Rigel Kentaurus. This star goes by another name, because it is brightest star in Centaurus. It's also one of the closest stars to our Sun.

15. What is the other name for this star? How far is it from the Sun?

Constellations seen from the Northern Hemisphere by Season

Summer

Aquila (Altair)
Corona Borealis
Cygnus (Deneb in the Northern Cross)
Draco
Hercules
Lyra (Vega)
Sagittarius (Center of Milky Way)
Scorpius (Antares)

Fall

Andromeda (Andromeda Galaxy)
Cepheus
Cassiopeia
Pegasus
Perseus (Algol)

Winter

Auriga (Capella)
Canis Major (Sirius)
Canis Minor (Procyon)
Gemini (Castor and Pollux)
Orion (Betelgeuse, Rigel and the Orion Nebula)
Taurus (Aldebaran and the Pleiades)

Spring

Bootes (Arcturus)
Cancer (Beehive Cluster)
Leo (Regulus)
Virgo (Spica)
Ursa Major (pointer stars)
Ursa Minor (Polaris)

Constellations seen from the Southern Hemisphere by Season