LUMINOSITY

Which star's colour is invisible in space by the human eyes?

• Red Star

• Yellow Star

• Green Star

• Orange Star

Choose the correct explanation(s)

• Blue stars are actually colder than red stars. Their low temperature makes them have a chilly environment which results in an outward blue colour.

• As the star gets hotter, the wavelength will decrease and moves further to the left, the ultraviolet end of the spectrum. Thus, bluer stars which are on the left of the spectrum are hotter than red stars.

• Blue stars are hotter than hot stars because they generally have a greater mass. This means that they have more energy to burn up for fusion in the core, resulting in higher temperatures than red stars.

• None of the above

Which property of a star is the brightness of a star at a standard distance?

• Apparent (magnitude) brightness
• Absolute (magnitude) brightness
• Luminosity
• Size of the star

The luminosity of the Sun, 𝐿𝐿⨀, is 3.828∗1026W. Polaris has a mass of 7.5𝑀𝑀⨀and a diameter 30 times that of the Sun. The difference between their absolute magnitudes is 8.47. What is the surface temperature on Polaris?

• 7600K

• 7400K

• 7200K

• 7000K

• 6800K

Which celestial body above is most likely to have the highest surface temperature?

• A

• B

• C

• D

Which of the following stellar spectral classes has the highest surface temperature?

• O

• A

• F

• K

Which of the following is the best approximate ratio of the brightness of a magnitude 1 star, to that of a

magnitude 3 star?

• 2

• 4

• 631/100

• 100/631

Is the star marked X belong to the main sequence stars?

• True

• False

Which pair is most likely to have stars with approximately equal radii?

• A

• B

• C

• D

• It is impossible to compare stellar radii using a H–R diagram.

What kind of star has the longest lifespan?

• A very massive star, like a blue giant

• An average sized star, like our Sun

• A star with low mass, like a red dwarf