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Approximately, what basic composition are all stars born with?

three-quarters hydrogen, one-quarters helium, no more than 2 percent heavier elements

A star's luminosity is the

total amount of light that the star radiates each second.

If the distance between us and a star is doubled, with everything else remaining the same, the luminosity...

remains the same, but the apparent brightness is decreased by a factor of four.

The spectral sequences sorts stars according to...

surface temperance.

The spectral sequence in order of decreasing temperature is...


When does a star become a main-sequence star?

when the rate of hydrogen fusion within the star's core is high enough to maintain gravitational equilibrium.

Which of the following best describes the axes of the Hertzsprung-Russell (H-R) diagram?

surface temperature on the horizontal axis and luminosity on the vertiaval axis

On the main sequence, stars obtain their energy...

by converting hydrogen to helium in their cores.

What happens to the rotation of a molecular cloud as it collapses to form a star?

The rotation rate increases and results in a disk of material around a protostar.

Suppose you measure the parallax angle for a particular star to be 0.25 arcesecond. The distance to this star is...

4 parsecs

What is the smallest mass a newborn star can have?

80 times the mass of Jupiter or .08 times the Sun's mass

Where would a brown dwarf be located on an H-R diagram?

below and to the right of the lowest part of the main sequence

The faintest star visible to the naked eye has an apparent visual magnitude of about...


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