A light year is a unit of
- A.Time
- B.Distance
- C.Brightness
- D.Mass
Correct answer
Explanation
The correct answer is B, distance. 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. The word year in its name misleads candidates into choosing time, and that is exactly the trap the examiner sets. Astronomers use the light year for distances to stars, so Proxima Centauri at 4.24 light years means that light from it takes four years and about three months to reach us. Option A, time, is measured in seconds, days and years. Option C, brightness, is measured by magnitude or by luminosity in watts. Option D, mass, is measured in kilograms, and in astronomy in solar masses. The two related units of distance worth remembering are the astronomical unit, the mean distance of the earth from the Sun, and the parsec, which equals about 3.26 light years.
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 →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
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A star is so far away that it is a point source of light.
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 →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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