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The approximate main-sequence lifetime of a star of spectral type O is

3 million years

How did astronomers discover the relationship between spectral type and mass for main sequence stars?

By measuring the masses and spectral types of main-sequence stars in binary systems.

The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster is the youngest?

The diagram shows main-sequence stars of every spectral type except O, along with a few giants and supergiants.

The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster is most likely to be located in the halo of our galaxy?

The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs.

You observe a star and you want to plot it on an H-R diagram. You will need to measure all of the following, except the star's


To calculate the masses of stars in a binary system, we must measure their

orbital period and average orbital distance

Sirius is a star with spectral type A star and Rigel is a star with spectral type B star. What can we conclude?

Rigel has a higher surface temperature than Sirius.

The star Vega has an absolute magnitude of about 4 and an apparent magnitude of about 0. Based on the definitions of absolute and apparent magnitude, we can conclude that

Vega is nearer than 10 parsecs from Earth.

A star with a parallax angle of 1/20 arcsecond is

20 parsecs away

Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore:

Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A.

Based on the definition of apparent brightness, which units are appropriate for its measurement?

watts per square meter

All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the characteristics of a star?

its mass and its stage of life

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