Astronomy Part 5

Front

How do astronomers measure the distance to a nearby star?

Back

They observe the apparent change in its position with respect to other, more distant stars over a period of six months.

Front

A star of magnitude +8 is

Back

fainter than a star of magnitude +5.

Front

A star of magnitude -1 is

Back

brighter than a star of magnitude +1.

Front

According to the inverse-square law, if two stars have the same luminosity and if one star is nine times farther away than the other, then

Back

the more distant star would be 81 times fainter.

Front

In the visible spectra of stars, absorption lines of hydrogen are produced when electrons are excited to higher levels (the Balmer series). If hydrogen absorption lines are very strong in the visible spectrum of a particular star, what is this star's surface temperature?

Back

very high temperature, about 40,000 K, because at lower temperatures too many hydrogen atoms have their electrons in the ground state (n = 1) and cannot absorb in the Balmer series.

Front

Why are the absorption lines from hydrogen very weak in the solar spectrum?

Back

The Sun's temperature is so low that very few electrons in hydrogen atoms are excited to the second energy level, from which absorption of visible light can occur.

Front

Which of the following sequences of stellar classification types shows stars in order of increasing surface temperature? B2, G6, G9, K0, K0, G9, G6, B2, K0, G6, G9, B2, B2, G9, G6, K0

Back

K0, G6, G9, B2

Front

A certain star is seen to have a relatively low surface temperature but a very high luminosity. What can we conclude from these observations?

Back

The star must be very large.

Front

A distant star of spectral type M is found to be very bright and easily visible from Earth. How would you describe it, and what would be its place in the Hertzsprung-Russell diagram?

Back

red supergiant; upper-right-hand corner of the H-R diagram

Front

If a star is found to evolve so that it moves from the main sequence to the red-giant area of the Hertzsprung-Russell diagram (remember, red stars are cool), which of the following changes will have occurred?

Back

The star will have expanded.