Astronomy in questions and answers
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Stars [Questions 1-21]

1. What is a star?

A star is a gaseous self-luminous body in space.

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2. Do all of the stars have names?

No, only about 250 of the brighter stars have names.

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3. How did the stars get their names?

The Babylonians were probably the first historical people to name the stars. Most of the names which have come down to us are Arabic, with some Persian, Greek, Latin and Babylonian names. Most of the Latin names are modern. The names of the stars came to us about 2,000 years ago. Some of them came 500 years ago.

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4. What star is nearest the Earth?

Which is the second nearest? The Sun is the nearest the Earth. The mean distance of the Sun from the Earth is 150 million kilometres. The distance from the Earth to the second nearest star, Proxima Centauri, is about 4.2 light years from the Sun. That distance translates into 40 billion (40,000,000,000,000) kilometres.

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5. How are the distances to the near stars measured?

The distances to the nearer stars are measured mathematically, by trigonometric parallax. "Parallax" is a word of Greek origin meaning difference in the apparent positions of an object.

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6. What is a parsec?

The word "parsec" is made up of the parts of the words "parallax" and "second". It means the distance from the Earth to a star whose parallax is one second of arc. There is no star as near as one parsec, for the parallax of the nearest star is 0.75". A parsec is 3.26 light years.

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7. How many stars can we see on a clear night?

A man can see between 3,500 and 4,000 stars.

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8. Why are some stars brighter than others?

In general, a star's brightness depends upon its distance from us, its temperature and its size. With stars of the same size and temperature, the nearer stars will appear to be the brighter. With stars at the same distance and of the same size, the hotter stars will be the brighter. With stars at the same distance and the same temperature, the larger stars will appear brighter.

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9. What does magnitude mean?

Magnitude is the measure of the brightness of a star or of any luminous body in the heavens.

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10. Do the stars have colour?

Yes. The colours most often seen in the stars are red, orange, yellow, white and blue. There are some violet stars and a few green stars.

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11. Do the colours of the stars have any significance?

Yes. Colours indicate star temperatures, they also tell which of the elements make up the stars. As a rule, the blue and the white stars are the hottest, while the red stars are cooler stars.

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12. How hot are stars?

The hottest stars have a surface temperature about 45,000C. The coolest visible stars are about 200C at their surfaces. The inside temperatures of all stars must be measured in the millions of degrees.

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13. How do we know the temperature of a star?

An instrument called a thermocouple indicates the amount of radiation we receive from a star. If the star's distance is known, its temperature can be calculated. The spectroscope will tell us of the behavior of the atoms that make up a star, and the laboratory gives us a criterion for the behavior of atoms of various elements at various temperatures. It is possible to estimate very closely the temperature of any star whose spectrum can be studied.

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14. How big are stars?

The smallest known stars are about the size of planets. The largest stars are hundreds of times the diameter of the Sun.

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15. What is a giant star?

A giant star is one whose diameter is between 10 times the diameter of the Sun and 100 times its diameter.

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16. Are the giants massive stars?

The largest star masses known are only 100 times the mass of the Sun, and such stars are very rare. The giants are large, cool stars, whose masses are about the mass of the Sun and go from 10 and sometimes 20 times of the Sun's mass.

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17. Are the giant stars hot stars?

Not as a rule, at least at their surface. There are very few hot stars that are larger than 10 times the diameter of the Sun.

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18. What is a supergiant star?

Stars which are larger than giants are supergiant stars. A supergiant star is one whose diameter is more than 100 times the diameter of the Sun.

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19. Are the supergiants massive stars?

The masses of the supergiants are 30 times the mass of the Sun, although, the volumes of such stars may be thousand of times the volume of the Sun.

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20. Are the supergiant stars hot stars?

No, as a rule, the supergiant stars are all of a low surface temperature - about 3,000C.

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21. What are the sizes of the supergiant stars?

The largest stars are about 3,000 times the diameter of the Sun. In kilometres, this is from about 5 thousand million kilometres in diameter to about 160 million kilometres.

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See also
• The Sun
• The Earth
• The Moon
• Mercury, Venus and Mars
• Jupiter, Saturn, Uranus, Neptune, Pluto
• Meteors and Comets
• The Constellations
• Galaxies
• Scientists and Astronomers
 
 
 

 
 
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