Classifying Stars
5 marks · NormalThe table below shows the classification of some stars by their surface temperature and colour:
| Star class | Surface temperature (K) | Colour |
|---|---|---|
| O | more than 33 000 | blue |
| B | 33 000 – 10 000 | blue-white |
| A | 10 000 – 7 500 | white |
| G | 6 000 – 5 200 | yellow |
| K | 5 200 – 3 700 | orange |
| M | 3 700 – 2 000 | red |
In which class would the Sun be placed? Give the class letter and colour.
A star shines with a yellow-white colour. Estimate its surface temperature range using the table.
Explain why a star that appears red is much cooler than a star that appears white.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) G, yellow
(b) 7 500 – 6 000 K · must show temperature range matches yellow-white
(c) Red stars emit less energy than white stars because surface temperature is lower; red stars have the lowest temperatures in the table, while white star classes are hotter. · must show red means lower temperature, white means higher temperature
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly states the Sun's class (G/yellow).
B2 (b) · 2 marks · Correctly gives a range 7 500–6 000 K for a yellow-white star (accept clear use of table).
B3 (c) · 2 marks · Explains using the idea that red stars are cooler; white stars are much hotter, so colour is linked to temperature.
Worked solution
a) The Sun is a G class star and appears yellow.
b) A yellow-white star is either class A (10 000–7 500 K) or towards the upper G range (6 000 K). So, its surface temperature range is 7 500 K to 6 000 K.
c) A red star is much cooler than a white star because red stars have lower surface temperatures, while white stars (class A) have much higher temperatures according to the table.