Constellations

1. Constellations By Jaclyn Schmitz

2. Stars • Our sun is one of about 200 billion stars in our galaxy (the Milky Way) • The sun is considered a very average star should have enough fuel to last another 4-5 billion years • There are other stars in our galaxy which are just like our sun but also ones which are smaller (the size of earth) and much larger (the size of the orbit of Jupiter) • Each of these stars have their own life cycle – some lasting only a few million years and others lasting billions of years

3. Do stars actually move? • Just like planets, stars also move. • We cannot see this movement, though, because the distance is so far that in order to see a change in position of the stars takes years and years • If we could travel ahead in time 20 millions years the constellations as we know them would look much different from what we see today.

4. Constellations • Stars form patterns in the sky • Using these patterns Greeks told stories of mythology about their Gods • There are 88 constellations that make up the sky • The best way to describe a constellation is a connect-the-dot drawing of picture in the sky

5. The North Star • The earth is tilted on an axis of 23.5 degrees • The top of the axis points North at the North star (also known as Polaris) • Polaris is located at the end of the handle of the Little Dipper • Other constellations fall around Polaris

6. Apparent movement of the constellations • Just like how the sun appears to rise in the east and set in the west, stars appear to move in our night sky • This is due to the fact that earth is tilted on an axis and rotates on it • As we rotate, everything in the sky seems to move! • It is from our position on earth that constellations seem to rotate and change position (see next slide) • The stars seem to rotate around the North star, which itself does not move

7. Different seasons – different stars • Stars stay where they are all year, so we can only see certain stars during certain times of the year • For example, I was born in the month of September which means my zodiac sign is Virgo. Every September you are able to see this constellation. At the opposite time of year, you cannot see it. • The reason why we can’t see the same stars all year round is because we are revolving around the sun. The sun blocks the view of the stars on the other side of it. It is so large that we can’t see any of the stars that stayed on the other side.

8. Circumpolar stars • We can see a few stars all year round – of course we can always see the North star. That is why it is so helpful for navigation. • We are also able to see the constellations close to the North star all year round • The big dipper and the little dipper • The stars we can see all year round are called circumpolar stars. At all times of the year we are able to see them.

9. 12:00 am From our perspective on earth this is how one full rotation would make the big dipper look in one night. Since it takes 24 hours for one rotation, each quarter turn would take 6 hours. 6:00am 6:00pm 12:00pm

10. January This movement of constellations could also be how they “move” throughout the year as we revolve around the sun. Each quarter turn would then be three months apart from each other April October July

12. Why Do We See Different Constellations During the Year? • If observed through the year, the constellations shift gradually to the west. This is caused by Earth’s orbit around our Sun. In the 
summer, viewers are looking in a different direction in space at night than they are during the winter. • What is the Zodiac?
Earth orbits our Sun once each year. Viewed from Earth, our Sun appears to trace a circular path. This path defines a plane called 
the plane of the ecliptic (or just the ecliptic). The zodiac is the group (or “belt”) of constellations that fall along the plane of the ecliptic. 
It is through these constellations that our Sun appears to “pass” during the year. While there are 12 astrological constellations of the 
zodiac, there are 13 astronomical zodiac constellations:  Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, 
Libra, Scorpius, Sagittarius, and Ophiuchus. The annual cycle of the zodiac was used by ancient cultures to determine the time of 
year. 

13. Vocabulary • Constellation: a group of stars that have been given a name • Zodiac sign: constellations that appear during certain 
months • Circumpolar: stars that are visible in the night sky all year 
round (Ursa Major, Ursa Minor, Cassiopeia) • Polaris: a star that points to the north. Our axis always 
points to Polaris. It is right above the north pole. You can 
see it all year round.

14. Star Brightness (Extension) • Star brightness is described in terms of magnitude • The brightest stars may be as much as 1 million times brighter than our sun • White dwarves are about 1000 times less bright