NOTES CHARACTERISTICS OF STARS
1. Astronomers estimate that there may be more than 200 billion stars in the universe.
2. Stars differ in many features:
A. Size B. Temperature C. Mass D. Brightness E. Color
3. While stars vary in a great many ways and size, there are certain forces which govern all
stars.
4. Astronomers gain knowledge about the vast number of stars by studying and examining
the details and forces of the closest stars.
5. Most stars are so far away that they appear as tiny points of light through the most
powerful telescopes.
6. Stars are divided into 5 Major Groups:
A. Medium-Sized Stars:
earth
B. Giant Stars:
or yellow in color
C. SuperGiant Stars:
-very few in number
yellow, or red in color
D. White Dwarfs:
distance across the continent of Asia
E. Neutron Stars:
ains of a Supernova
7. Astronomers can determine the composition of a star using a spectroscope
8. A spectroscope is an instrument which identifies the elements by the colors that they
give off.
9. Every element gives off light when it becomes hot enough; each element gives off its own
special color.
10. The most important part of the spectroscope is the prism. A prism can break up white
light into a rainbow (the spectrum).
11. A spectroscope separates the light into colored lines of the spectrum.
12. Using the spectroscope, Astronomers discovered most stars have the same general
composition.
13. The most common element found in stars is hydrogen, the lightest gas.
14. The second element is helium, together they make up 96-99% of a star’s mass.
15. All other elements in a star make up less than 4% of the mass. These include: oxygen,
neon, carbon, and nitrogen.
16. Stars come in many colors; Astronomers can determine its surface temperature by the
color of the star. The sun is a yellow star.
17. The temperature of the hottest star is about 50,000o C, and shines with a blue white
light.
18. The temperature of the coolest star is about 3,000o C and is called a red star. Most
star’s surface temperatures are between the two extremes.
19. Brightness of a star depends on its size, surface temperature, and distance from earth.
The brightness of most stars is constant.
20.Apparent Magnitude: the brightness of a star as it appears from earth.
21. Absolute Magnitude: the amount of light a star actually gives off.
22.Variable stars are stars that vary in brightness.
23.Pulsating variable stars are one type of variable star that changes size and brightness in
regular cycles.
24.The North Star, Polaris, changes from bright to dim and back again in a 4 day cycle.
25.Astronomers call these pulsating stars, Cepheid Variables, because the first one was
discovered in a group of stars called Cepheus.
26.The HERTZSPRUNG-RUSSELL DIAGRAM is a diagram based on a relationship
between the absolute magnitude and the temperature of stars discovered by
astronomers Ejnar Hertzsprung (Danish) and Henry Norris Russell (American) in the early
1900’s.
27.They discovered that as the absolute magnitude of a star increases, the temperature
usually increases. The Hertzsprung-Russell is the single most important diagram
astronomers use today.
28.Main Sequence is the area from the upper left corner to the lower right corner. 90% of
the stars in the sky fall into this area.
29.The upper left corner of the main sequence is for the hottest stars that shine blue or
blue-white light. The lower right corner is for the cool, dim stars.
30.The other 10% appear above or below the main sequence line, for example giants and
white dwarfs.