6. We observe twinkling of stars due to

1. 1. frequent and periodic fluctuation of temperature of the surface

   
   
   

   2. constant change of refractive index of the medium between the stars and the Earth because of temperature variation

   
   
   

   3. great distance of stars from the Earth

   
   
   

   4. rise and fall of gaseous ball of fire inside the stars

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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7. The permanent tilt of the earth's axis and the revolution of the earth its orbit together cause

1. 1. Day and night

   
   
   

   2. Varying lengths of day and night at different times of the year

   
   
   

   3. Differences in time between place on different meridian

   
   
   

   4. The deflection of wind

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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8. When the sun is vertically overhead along the Tropic of Capricon at midday

1. 1. Days and nights are of equal length in the Northern Hemisphere

   
   
   

   2. Nights are longer than days in the Southern Hemisphere

   
   
   

   3. Days and nights are equal length at the poles

   
   
   

   4. Night is equal to 24 hours of the North pole

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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9. The 'blue moon'phenomenon occurs

1. 1. When two full moons occur in the same month

   
   
   

   2. When four full moons appear in two consecutive months of the same calender year

   
   
   

   3. When two full moons appear in the same month thrice in a calendar year

   
   
   

   4. None of the above

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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10. The term 'syzygy' is reffered to when the

1. 1. Earth is at perihelion and moon at perigee

   
   
   

   2. Earth is at apehelion and moon at apogee

   
   
   

   3. Moon and Sun are at right angles with reference to tthe earth

   
   
   

   4. Moon, Sun and Earth lie along a straight line

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   NA

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