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11. When can the chromosphere be seen?
The chromosphere can be seen during a total eclipse of the Sun. At these times, the Moon passes between the Earth and the Sun, and the
chromosphere can be seen. At other times, the chromosphere may be seen by means of a spectrohelioscope.
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12. What is the corona?
The corona is the outermost layer of
the Sun's atmosphere. The corona is composed of gases that
are expelled from the Sun constantly.
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13. How big is the corona?
The rays of the corona extend for
many millions of kilometres into space.
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14. When can the corona be seen?
The corona can be seen only
at times of a total eclipse of the Sun or by means of a special
instrument called the coronagraph.
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15. What are sun-spots?
Sun-spots are dark areas in the photosphere.
Sun-spots do not travel across the surface of the
Sun but are carried around by the Sun's rotation.
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16. How big may sun-spots be?
Sun-spots come in different
sizes. The smallest are a few hundred kilometres in diameter.
There are probably sun-spots which are so small that they
cannot be seen, even through a telescope. On the other hand
there are spots whose area is several thousand million square
kilometres. One of the largest spots appeared in April, 1947, and had an area of 9.65 thousand million square kilometres.
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17. Are sun-spots black?
No. They appear dark only by contrast with the bright general surface of the Sun.
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18. Are sun-spots cooler than the rest of the Sun?
Yes. Since the gases in the areas of sun-spots are radiating less energy
than the gases of the general surface of the Sun, temperature
within the area of a sun-spot is about l,000°C lower than
the temperature of the normal surface of the Sun.
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19. How long do sun-spots last?
The larger sun-spots last
longer than the smaller. Sun-spots which are of about the
minimum diameter that can be seen last from one to four
days. Less than 10% of the sun-spots last longer.
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20. Are there always spots on the Sun?
No. There have been
times when there were no spots on the Sun. The cycle of sun-
spots is one of the most interesting studies in astronomy.
The sun-spot cycle is not regular, but, over the years, an
average period of 11.3 years passes between one minimum
of sun-spot activity and the next. There are periods of months
at the time of a sun-spot minimum when no spots at all can
be seen on the Sun.
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21. Do sun-spots have any effect upon the Earth?
Sun-spots
have a very definite effect upon the Earth. Sun-spot activity is closely connected with different phenomena in the
atmosphere of the Earth: magnetic storms, aurorae (auroras). During
magnetic storms radiotelephone service and television sets
work badly. There is a connection between sun-spot cycles
and the weather.
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