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  3. Eta Carinae As possibly the galaxy’s （银河）most massive star, Eta Carinae is...

Eta Carinae As possibly the galaxy’s （银河）most massive star, Eta Carinae is...

admin2020-12-24  50
问题 Eta Carinae
As possibly the galaxy’s （银河）most massive star, Eta Carinae is now engaging in some very unusual behaviour. Australian astronomers, being in the Southern Hemisphere（半球），are at)le to observe it clearly.
In the 19th century, Eta Carinae was for a time the third brightest star in the sky. It has now become less bright so that binoculars ( 双筒望远镜）are needed to see it. “ It seems to be brightening and becoming less bright over a period of many years” ，said Dr Bob Duncan
from the Australia Telescope National Facility.
While it is not unusual for stars to vary in brightness, the period is usually much shorter. “ Since 1992 it has become four times brighter，and then last year it began to drop dramatically, he said.
The problem in observing Eta Carinae is that it has been surrounded by a cloud of gas and dust, making it hard to see the star directly. However, radio waves and infrared light （红外线）can pass through this cloud，so telescopes that receive these wavelengths can observe what is occurring.
Eta Carinae is of particular interest to astronomers because it seems to be in its death throes （剧痛）. Being so large it will end up as a supernova （超新星）. There has not been a supernova in our geilaxy since the invention of the telescope. While a 1987 explosion in a nearby galaxy gave astronomers plenty of valuable data, they are hungry for an even closer look.
Eta Carinae has other unique features, and is the only star known to produce an ultraviolet （紫外线）laser that is brighter than that produced by the Sun. Lasers have been observed in other frequencies from a few stars.
The word "period" in Paragraph 3 means the length of time
选项 A over which stars vary in brightness.
B for which Eta Carinae’s brightening lasts.
C Eta Carinae takes to become a supernova.
D it takes the laser from Eta Carinae to travel to the earth.
答案A
解析
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