Super fact 102: Stars twinkle but planets do not. Planets reflect sunlight, like the moon, whereas stars emit intense light like the sun. However, stars are thousands of times further away.
The Sun and the Moon appear to have roughly the same sized disk in the sky, about 0.5 degrees of arc, because the Sun is roughly 400 times wider than the Moon but also about 400 times farther away. However, the moon, which reflects sunlight but does that emit any, is much fainter than the sun in our sky. The Sun provides approximately 400,000 times more light to Earth than the full Moon. If you were to move the sun farther away until it provided the same amount of light as the moon you would have to move the sun 632 times farther away until it became a tiny point in comparison to the moon.
The planets in our solar system, Venus, Jupiter, Mars, Mercury, Saturn, etc., appear in the sky as small discs reflecting light whereas the stars appear as intense points of light with a disc diameter that is thousands of times smaller than that of the planets. However, we can’t see the difference with the naked eye. Both planets and stars appear like points of lights to us, but the difference in disc size in the sky is very big.
Because stars are tiny intense points of light Earth’s atmosphere can easily refract (bend) their light. This is known as scintillation. I can add that the light from stars that are low in sky go through more atmosphere and therefore twinkle more. Since planets appear as tiny discs rather than tiny points, planets create a steadier beam of light, which averages out atmospheric turbulence. In addition, dust particles in space and in the atmosphere can more easily block the light from stars compared to that of planets, because the planets have much larger discs in the sky (thousands of times larger).
Since this fact is not scientifically under question, a lot of people don’t know it, and it is kind of important to anyone interested in the night sky, I consider it a super fact. I should say that I borrowed this super fact from Jacqui Murray’s blog worddreams.
Planets Reflect Light like the Moon
Planets reflect light. They don’t shine and emit light like the sun or the stars.
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