Astronomy (chapter 15)

Approximately, what basic composition or a star is born with?

• 1/4 hydrogen, 3/4 helium, no more than 2% heavier elements

• Half hydrogen, half helium, no more than 2% heavier elements

• 3/4 hydrogen, 1/4 helium, no more than 2% heavier elements

• 90% hydrogen, 10% helium, no more than 1% heavier elements

Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?

• Mass they are formed with

• Color they are formed with

• Time they are formed

• Location where they are formed

What are the standard units for luminosity?

• J

• Watts

• Newtons

• Kilograms

A stars luminosity is the?

• Total amount of lights at the store will radiate over its entire lifetime

• Total amount of light that the star radiates each second

• Surface temperature of the star

• Apparent brightness of a star in our sky

What are the standard units for apparent brightness?

• Watts per second

• Watts

• J

• Watts per square meter

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

• Is decreased by a factor of four, but the apparent brightness remains the same

• Remains of the same, but the apparent brightness is decreased by a factor of two

• Is decreased by a factor of four, and the apparent brightness is decreased by factor of foUr

• Remains the same, but the apparent brightness is decreased by a factor of four

Why do astronomers often measure the visible light apparent brightness instead of the total apparent brightness of a star?

• Most stars do not put a light in other ranges of the spectrum

• Astronomers are lazy

• They’re identical for most stars

• In order to measure the total apparent brightness of a star, you must measure its brightness in all wave links, and this is difficult to do. The only wavelengths you can measure from the surface of earth are visible in radio wavelengths.

Suppose you measure the parallax angle for a particular star to be .1 arc seconds. The distance to the star is?

• 10 light years

• 10 parsecs

• .1 light year

• Impossible to determine

The most distant stars we can measure stellar parallax for are approximately?

• In the Andromeda galaxy

• 100 parsecs away

• 10,000 parsecs away

• Halfway across the Milky Way galaxy

Which of the following statements about a parent and absolute magnitude is true?

• All of the above are true

• Star Wars apparent magnitude one is brighter than one with apparent magnitude to

• The magnitude system that we sue now is based on the system used by the ancient Greeks over 2000 years ago

• The absolute magnitude of a star is another measure if it’s luminosity