1. Chapter 26: Stars and Galaxies
Section 1: Stars

2. Stars 1
Constellations
Early cultures observed patterns of stars in the night sky called constellations.
From Earth, a constellation looks like spots of light arranged in a particular shape against the dark night sky.

3. Stars 1
Constellations
This figure shows how the constellation of the mythological Greek hunter Orion appears from Earth.

4. Modern Constellations
Stars 1
Modern Constellations
Modern astronomy divides the sky into 88 constellations.
You probably know some of them.

5. Modern Constellations
Stars 1
Modern Constellations
The Big Dipper, in red, is part of the constellation Ursa Major.
It is visible year-round in the northern hemisphere.

6. Circumpolar Constellations
Stars 1
Circumpolar Constellations
As Earth rotates, Ursa Major, Ursa Minor, and other constellations in the northern sky circle around Polaris.
Because of this, they are called circumpolar constellations.

7. Circumpolar Constellations
Stars 1
Circumpolar Constellations
The constellations appear to move because Earth is in motion.
The stars appear to complete one full circle in the sky in about 24 h as Earth rotates on its axis.

8. Absolute and Apparent Magnitudes
Stars 1
Absolute and Apparent Magnitudes
When you refer to the brightness of a star, you can refer to its absolute magnitude or its apparent magnitude.
The absolute magnitude of a star is a measure of the amount of light it gives off.

9. Absolute and Apparent Magnitudes
Stars 1
Absolute and Apparent Magnitudes
A measure of the amount of light received on Earth is the apparent magnitude.
A star that's dim can appear bright in the sky if it's close to Earth, and a star that's bright can appear dim if it's far away.

10. Stars 1
Measurement in Space
How do scientists determine the distance from Earth to nearby stars?
One way is to measure parallax—the apparent shift in the position of an object when viewed from two different positions.

11. Stars 1
Measurement in Space
Extend your arm and look at your thumb first with your left eye closed and then with your right eye closed.
Your thumb appears to change position with respect to the background.

12. Stars 1
Measurement in Space
Now do the same experiment with your thumb closer to your face.
What do you observe?
The nearer an object is to the observer, the greater its parallax is.

13. Stars 1
Measurement in Space
Astronomers can measure the parallax of relatively close stars to determine their distances from Earth.

14. Stars 1
Measurement in Space
Distances between stars and galaxies are measured in light-years.
A light-year is the distance that light travels in one year.
Light travels at 300,000 km/s, or about 9.5 trillion km in one year.

15. Properties of Stars 1 The color of a star indicates its temperature.
Hot stars are a blue-white color.
A relatively cool stars looks orange or red.

16. Stars 1
Properties of Stars
Astronomers study the composition of stars by observing their spectra.
When fitted into a telescope, a spectroscope acts like a prism.
It spreads light out in the rainbow band called a spectrum.

17. Stars 1
Properties of Stars
When light from a star passes through a spectroscope, it breaks into its component colors.
Dark lines are caused by elements in the star's atmosphere.
Like a fingerprint, the patterns of lines can be used to identify the elements in a star's atmosphere.

18. Question 1 1 Patterns of stars in the night sky are called __________.
Section Check 1
Question 1
Patterns of stars in the night sky are called __________.
A. constellations
B. magnitudes
C. orbits
D. parallaxes

19. Section Check 1
Answer
The answer is A. People in early cultures imagined that the constellations represented characters or familiar objects.

20. Question 2 1 Which of the following is NOT a constellation?
Section Check 1
Question 2
Which of the following is NOT a constellation?
A. Cassiopeia
B. Polaris
C. Ursa Major
D. Ursa Minor

21. Answer 1 The answer is B. Polaris is also known as the North Star.
Section Check 1
Answer
The answer is B. Polaris is also known as the North Star.

22. Section Check 1
Question 3
The__________ of a star is a measure of the amount of light it gives off.
A. absolute magnitude
B. apparent magnitude
C. distance
D. spectra

23. Section Check 1
Answer
The answer is A. Absolute magnitude is calculated using the star’s apparent magnitude and its distance.