Astronomy: Stellar Spectral Classification Sequence from Hottest to Coolest Practice
Practice ordering O, B, A, F, G, K, and M stars by temperature and color
Astronomy: Stellar Spectral Classification Sequence from Hottest to Coolest Practice
Practice ordering O, B, A, F, G, K, and M stars by temperature and color
Astronomy - Grade 9-12
- 1
Write the stellar spectral classification sequence from hottest to coolest.
A common memory phrase is: Oh Be A Fine Girl/Guy, Kiss Me.
The sequence from hottest to coolest is O, B, A, F, G, K, M. - 2
Put these spectral classes in order from hottest to coolest: K, A, O, G, M.
The correct order is O, A, G, K, M because O stars are the hottest and M stars are the coolest. - 3
Put these spectral classes in order from coolest to hottest: B, F, M, K, O.
Reverse the hottest-to-coolest sequence O, B, A, F, G, K, M.
The correct order from coolest to hottest is M, K, F, B, O. - 4
A star is classified as spectral type A. Another star is classified as spectral type K. Which star has the higher surface temperature, and why?
The A-type star has the higher surface temperature because A comes before K in the hottest-to-coolest sequence O, B, A, F, G, K, M. - 5
A diagram shows four stars labeled B, G, M, and F. Rank the stars from highest surface temperature to lowest surface temperature.
Compare each letter to the sequence O, B, A, F, G, K, M.
The correct ranking from highest surface temperature to lowest surface temperature is B, F, G, M. - 6
Match each spectral class to its most typical visible color: O, A, G, M. Use the choices blue, white, yellow, and red.
O stars are typically blue, A stars are typically white, G stars are typically yellow, and M stars are typically red. - 7
The Sun has spectral class G2. Based on its class, is the Sun hotter than a K star or cooler than a K star? Explain.
Only compare the letter classes first: G and K.
The Sun is hotter than a K star because G comes before K in the hottest-to-coolest sequence. - 8
A star has a surface temperature of about 30,000 K. Another star has a surface temperature of about 3,500 K. Which one is more likely to be an O or B star, and which one is more likely to be an M star?
The star at about 30,000 K is more likely to be an O or B star because those classes are very hot. The star at about 3,500 K is more likely to be an M star because M stars are the coolest in the sequence. - 9
A student says, "Red stars are hotter than blue stars because red looks like fire." Correct the student's statement using stellar spectral classification.
Star color is related to surface temperature, and blue light corresponds to hotter objects than red light.
The statement is incorrect. In stars, blue stars are hotter than red stars. O and B stars are blue or blue-white and are hottest, while M stars are red and coolest. - 10
Use the simplified H-R diagram idea that temperature increases to the left. If spectral classes are shown along the bottom from left to right, what order should they appear in?
They should appear from left to right as O, B, A, F, G, K, M because the left side is hottest and the right side is coolest. - 11
Two stars are labeled F5 and F9. Within the same spectral class, lower numbers are hotter and higher numbers are cooler. Which star is hotter?
Compare the subtype numbers 5 and 9 after confirming both stars are class F.
The F5 star is hotter because within a spectral class, lower subtype numbers are hotter than higher subtype numbers. - 12
Rank these stars from hottest to coolest: A0, A9, B8, G2, M1, K5. Remember that the letter class matters first, and within a class, lower subtype numbers are hotter.
Sort by letter class first using O, B, A, F, G, K, M, then use the subtype number only if the letters match.
The correct order from hottest to coolest is B8, A0, A9, G2, K5, M1. The letter sequence determines the main order, and A0 is hotter than A9 within class A.