What is the reason behind the twinkling of stars?
- A.Scattering of light by dust particles
- B.Internal reflection of light by clouds
- C.Atmospheric refraction of star light
- D.Dispersion of light by water droplets
Correct answer
Explanation
The correct answer is C, atmospheric refraction of star light. A star is so far away that it is a point source of light. Its light passes through layers of air of different densities and temperatures that keep moving, so the light is refracted by amounts that change from moment to moment and the apparent position and brightness of the star keep changing; this is seen as twinkling. Planets are much nearer and act as a collection of point sources, whose variations average out, so they do not twinkle appreciably, and a star seen from outside the atmosphere does not twinkle at all. Option A, scattering by dust particles, explains the blue colour of the sky and the red colour of the setting sun, not twinkling. Option B is wrong because clouds block starlight rather than reflect it in this way. Option D, dispersion by water droplets, is the cause of the rainbow.
Read the full article: Space Science: Stars, Galaxies and Satellites Notes
Practice Questions
View allThe source of the Sun's energy is
- A.Fusion of heavy nuclei
- B.Fusion of lighter nuclei
- C.Fission of light nuclei
- D.Fission of heavy nuclei
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In the core of the Sun, at a temperature of about fifteen million kelvin, four hydrogen nuclei combine through the proton-proton chain to form one helium nucleus.
Read the full explanation →Once a satellite has been launched into orbit, the only force governing its motion is the force of ______.
- A.gravity
- B.elasticity
- C.friction
- D.fuel driven
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A satellite is given the required height and speed by its launch vehicle, and after that no engine is needed: the gravitational pull of the earth alone acts on it and provides the centripetal force that keeps it in a curved path, so the satellite keeps falling towards the earth…
Read the full explanation →A light year is a unit of
- A.Time
- B.Distance
- C.Brightness
- D.Mass
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A light year is the distance travelled by light in vacuum in one year, which is about 9.46 times ten to the power twelve kilometres, or roughly nine and a half trillion kilometres.
Read the full explanation →Which is the nearest star to the earth after the Sun?
- A.Sirius
- B.Proxima Centauri
- C.Polaris
- D.Betelgeuse
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Being a red dwarf it cannot be seen with the naked eye, although it is the closest star to us after the Sun.
Read the full explanation →A geostationary satellite completes one revolution around the earth in
- A.90 minutes
- B.12 hours
- C.24 hours
- D.365 days
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A geostationary satellite is placed in a circular orbit about 35,786 kilometres above the equator, where its period of revolution equals the period of rotation of the earth about its axis, and it moves from west to east like the earth, so it appears to stay over the same point…
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