The twinkling of a star is due to :
- A.atmospheric reflection of starlight.
- B.atmospheric refraction of starlight.
- C.continuous change in the position of the star.
- D.oscillation of starlight.
Correct answer
Explanation
The correct answer is B, atmospheric refraction of starlight. Starlight bends as it passes through air layers of changing density, and because these layers keep moving, the star seems to flicker.
A star is so far away that it acts as a point source of light. Its light passes through the Earth's atmosphere, where temperature and density vary from layer to layer and keep shifting. The refractive index changes along the path, so the light bends by a slightly different amount from moment to moment. The apparent position of the star wavers a little and the amount of light entering the eye rises and falls, which we see as twinkling. Planets are much closer and look like small discs; the changes from different points cancel out, so planets do not twinkle.
Option A is wrong because the effect is bending, not reflection. Option C is wrong because the star itself does not keep moving. Option D is wrong because starlight does not oscillate in brightness at its source.
Exam tip: refraction explains twinkling stars, early sunrise and late sunset; scattering explains the blue sky.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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