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?{{B}}Sunspots{{/B}} ? ?It’s not surprising that sunspots (太阳黑子)
were observed by ancient astronomers (天文学家). The largest sunspots on the sun can
be seen without a telescope. It was not until the invention of the telescope
(望远镜) in the early 17th century, however, that systematic studies of
sunspots could be undertaken. The great astronomer Galileo was among the first
to make telescopic observations of sunspots. ? ?Sunspots are
regions of extremely strong magnetic fields (磁场) found on the sun’s surface. A
sunspot has a dark central core known as the umbra. The umbra is surrounded by a
dark ring called the penumbra, where the magnetic field, spreads outward.
Sunspots appear dark because they are giving off less radiation. They are cooler
than the rest of the sun’s surface. ? ?Sunspots are frequently
observed in pairs or in paired groups. The members of a spot pair are identified
as the leading spot and the following spot. They are identified by their
position in the pair in terms of the direction in which the sun rotates
(旋转). ? ?The number of sunspots at any one time varies. A large
spot group may consist of as many as 10 groups and 300 spots across the sun. The
number of spots changes in a fairly regular pattern called the sunspot cycle.
The largest number occurs about every 11 years. At sunspot minimum, there are at
most just a few small spots. ? ?The average lifetime of an
individual spot group is roughly one solar rotation, which is about 25 days. The
most persistent large spots, however, can survive for two to three
months.
? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ?
?{{B}}Sunspots{{/B}} ? ?It’s not surprising that sunspots (太阳黑子)
were observed by ancient astronomers (天文学家). The largest sunspots on the sun can
be seen without a telescope. It was not until the invention of the telescope
(望远镜) in the early 17th century, however, that systematic studies of
sunspots could be undertaken. The great astronomer Galileo was among the first
to make telescopic observations of sunspots. ? ?Sunspots are
regions of extremely strong magnetic fields (磁场) found on the sun’s surface. A
sunspot has a dark central core known as the umbra. The umbra is surrounded by a
dark ring called the penumbra, where the magnetic field, spreads outward.
Sunspots appear dark because they are giving off less radiation. They are cooler
than the rest of the sun’s surface. ? ?Sunspots are frequently
observed in pairs or in paired groups. The members of a spot pair are identified
as the leading spot and the following spot. They are identified by their
position in the pair in terms of the direction in which the sun rotates
(旋转). ? ?The number of sunspots at any one time varies. A large
spot group may consist of as many as 10 groups and 300 spots across the sun. The
number of spots changes in a fairly regular pattern called the sunspot cycle.
The largest number occurs about every 11 years. At sunspot minimum, there are at
most just a few small spots. ? ?The average lifetime of an
individual spot group is roughly one solar rotation, which is about 25 days. The
most persistent large spots, however, can survive for two to three
months.
In the last paragraph the word "persistent" means
A.important B.effective C.enduring D.visible
单选集填空
