Friday, 16 October 2015


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Looking at the sky on a starry night is fantastic, but how do you distinguish between a star and planet?

There are several ways to tell whether that point of light you’re seeing is a planet or a star. A common method to distinguish between them is to see if the light appears to twinkle, change its colour or brightness. Another is to look at the movement of the planets and stars.


Stars are enormous but they are so far away that they appear very, very small. Unlike planets stars twinkle.  This is because the light for the star gets refracted (bent) as it passes through the different layers of the Earth's atmosphere.

Planets in our solar system are much closer to the Earth, and because they are closer they appear larger than stars. It is the sunlight that is being reflected off the planet that makes planets visible to us at night. The amount the light bends in Earths atmosphere is much smaller than that of a star compared to how big the planet looks and consequently  planets do not twinkle. 

So if you see a bright, non-twinkling light along that path, there’s a good chance that it’s a planet. However, it is important to note that sometimes the Earth’s atmosphere is moving around so much or has such a large amount of pollution that even the light from planets can appear to twinkle. 


Whilst stars do appear to change position in the night sky, they do so all together. In contrast planets move in specific orbits, independent of the motion of the stars, following the ecliptic path that the sun follows from east to west.

  • Stars twinkle at night.
  • A star has its own light.
  • A star has very high temperature.
  • The relative positions of the stars do not undergo any noticeable change.
  • Since the stars are very far away, the telescope can only make them look brighter but not larger.
  • There are billions of stars in the celestial sphere.


  • Planets do not twinkle
  • A planet has no light of its own. It shines by reflecting the light of the sun.
  • Planets have low temperatures.
  • Since planets are very mush closer to the earth than the stars are, their motion around the sun is noticeable as a daily shifting of their relative positions in the sky.
  • Most planets on the other hand are near enough to the earth to be magnified by the telescope.
  • There are only nine planets in the solar system. 

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