Measuring Stars

Two stars are the same distance from Earth. One is larger than the other. How do the brightness and temperatures of the stars differ with size?

• The smaller star is fainter and cooler

• The smaller star is brighter and hotter

• The larger star is brighter, but not necessarily hotter

• The larger star is cooler, but not necessarily brighter

Which physical property of a star is an indicator of its temperature?

• Mass

• Color

• Brightness

• Distance from Earth

The table below shows the surface temperature of a number of stars.

SURFACE TEMPERATURES OF STARS

Star Temperature (Kelvin)

Alpha Centauri B 5,300

Proxima 2,700

Sirius A 9,000

The Sun 5,800

Which star listed in the table appears the reddest?

• Alpha Centauri B

• Proxima

• Sirius A

• The Sun

Which properties would be most useful for the classification of a star recently discovered by an astronomer?

• temperature, solar flare activity, number of surrounding planets, and size

• temperature, size comparison to our sun, solar flare activity, and luminosity

• apparent magnitude, temperature, luminosity or absolute brightness, and size

• apparent magnitude, temperature, distance from the Milky Way, and presence of dark spots

Which physical property is the brightness of a star as seen from Earth?

• apparent magnitude

• radiation zone

• temperature

• color

Stars can be organized by size and temperature into four groups: dwarf stars, main sequence stars, giant stars, and supergiant stars. Into which group does the Sun most likely fall?

• dwarf stars, because the Sun is much smaller than most other stars

• giant stars, because the Sun is much larger than most other stars

• supergiant stars, because the Sun is one of the largest stars

• main sequence stars, because the Sun is of average size

Main sequence stars appear as a band on Hertzsprung-Russell (HR) diagrams. The HR diagram below shows the relationship between absolute brightness and temperature. Absolute brightness is measured here using a brightness scale, called absolute magnitude.

In a main sequence star, what is the relationship between a star’s absolute brightness (measured as absolute magnitude) and its temperature?

• The lower the temperature, the brighter the star

• The higher the temperature, the brighter the star.

• Most stars have the same temperature, but differ in absolute brightness

• Most stars have the same absolute brightness, but differ in temperature

The brightness of a star as seen from Earth is its apparent magnitude. How is apparent magnitude different from absolute magnitude?

• Apparent magnitude depends on the size of a star; absolute magnitude does not

• Apparent magnitude depends on the color of a star; absolute magnitude does not.

• Apparent magnitude depends on the temperature of a star; absolute magnitude does not.

• Apparent magnitude depends on the distance of a star from Earth; absolute magnitude does not

The Sun is classified as a "G" main sequence star. The Hertzsprung-Russell diagram indicates that, because the Sun is a "G" main sequence star, its surface temperature is

• between 6,000 K and 8,000 K

• between 4,000 K and 6,000 K

• greater than 10,000 K

• less than 4,000 K

The table below shows the properties of several stars. Use the table and your knowledge of stars to answer the question. Suppose you knew the surface temperature of Polaris. Which star would you expect to have a temperature most similar to that on Polaris?

Star Name Color

Rigel Blue

Vega White

Arcturus Orange

Betelgeuse Red

Polaris Yellow-white

• Vega

• Rigel

• Betelgeuse

• Arcturus