SDSS constellations

Discovering your constellations in SDSS data 1 star


Scorpius, the Scorpion
Copyright Richard Dibon-Smith.
Courtesy of
The Constellations web page

People have looked at the sky for thousands of years. When ancient people looked up, they saw the same thing you see today: beautiful stars. They saw patterns in the stars. Today, we call these patterns “constellations.”

You may have heard of some famous constellations, like Orion the Hunter. Astronomers today recognize 88 constellations, and we use them to divide the sky into 88 regions, as a cosmic address of sorts. This makes objects in the sky easier to find. Sometimes when astronomers talk about something in the sky, they often name it after the constellation it is closest to. For example, the large spiral galaxy M31 is near the constellation Andromeda. Astronomers call it the Andromeda Galaxy. To learn about how you can connect some of the official 88 constellations to SDSS images, try our Constellations activity.


Here, you will make your own.


Part 1 – What are constellations?


Let’s start with a simple example: a made-up constellation. Your teacher will divide you into two groups, and they will give you a sheet with a made-up collection of stars. Study it, then look at the pictures below. Pretend you are looking at stars in the sky. What do you see?


Someone from your group should describe what you see to the rest of the class. What did the other group see? Can you see what they saw?
Some will have seen a dove, others a horse, and others something else entirely.

This activity shows what ancient people did when they saw the stars. You can think of yourself as a member of an ancient culture. When you looked at the sky and saw those stars, you saw a dove or a horse. Whenever you looked at those stars, that’s what you saw.

The other group was like another ancient culture. They saw the other shape (horse or dove) – then every time they looked at those stars, they saw that shape.

Of course, there aren’t really doves or horses in the sky – just stars.The ancient people saw the patterns in the stars that they had always seen, just likeyou saw the pattern you had seen from your handout.

Now that you understand what constellations are, let’s look at a real constellation.

Part 2 – the stars of Orion

Let’s have a closer look at the constellation of Orion:

OrionThe Constellation Orion
Click on the image for a larger view.
Copyright Bernd Mienert. Courtesy of the Astronomical Image Data Archive.


When the ancient Greeks saw Orion, the shape reminded them of a hunter. The bright stars in the four corners were his shoulders and feet. The three horizontal stars in the middle were his belt. The three vertical stars below were his sword.

The Greeks told a story about Orion. He was a brave but proud hunter who was killed by a scorpion. When he died, the gods put him in the sky to remember him.

Study the picture of Orion above. Orion consists of seven major stars: two for his shoulders, two for his feet,and three for his belt. Copy the position of the stars to a piece of paper, and number the stars from 1 to 7, with the number 1 being the star that you think is closest to Earth.

Each star has a name, and astronomers have measured how bright and how far away each star is.

Astronomers measure how bright a star is with a number called magnitude. The brighter the star, the lower the magnitude, and a difference of 5 in magnitude means a factor of 100 difference in brightness.


The stars to the left are magnitude 13 and 18, so they differ by a factor of 100. Similarly, a magnitude 1 star is 100 times brighter than a magnitude 6 star. This might seem confusing to you, but astronomers have used magnitude for thousands of years.

Astronomers measure distance in light-years. One light-year is the distance light travels in one year: 9,458,000,000,000 kilometers. A light-year is a long way: to go one light-year in the Space Shuttle would take you about 40,000 years!

The table below shows magnitudes and distances for the seven stars that make up Orion.

Now number the stars in your drawing according to how far away they are, using the distances in the table below. Do they have the same numbers as you had guessed before? If not, can you think of why not?

Star Name

Part of Orion


Distance (light-years)


Left shoulder




Left foot




Right shoulder




Right foot




Left belt




Center belt




Right belt




Part 3 – Discovering your own SDSS constellations

You are now ready to discover new constellations in SDSS images and plates.



SDSS has taken so many images and spectra of objects in the sky, that many of them have never been looked at by a human – I wonder what you will find?

To discover constellations using photographs of the sky, start here:

Discovering constellations in SDSS imaging

To discover constellations useing SDSS plates, start here: (N.B.: this activity requires a physical SDSS plug plate)