如何利用卫星测量星体重量-凯发k8官网

如何利用卫星测量星体重量
文章来源:未知 文章作者:meng 发布时间:2010-10-18 03:27 字体: [ ] 
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how do 1 weigh a star that's trillions of miles away and way too big to fit on a bathroom scale(体重秤) ? in most cases they can't, although they can get a best estimate using computer models of stellar structure. new work by astrophysicist(天体物理学家) david kipping says that in special cases, we can weigh a star directly. if the star has a planet, and that planet has a moon, and both of them cross in front of their star, then we can measure their sizes and orbits to learn about the star.

"i often get asked how astronomers weigh stars. we've just added a new technique to our toolbox for that purpose," said kipping, a predoctoral fellow at the harvard-smithsonian center for astrophysics.

astronomers have found more than 90 planets that cross in front of, or 2, their stars. by measuring the amount of starlight that's blocked, they can calculate how big the planet is relative to the star. but they can't know exactly how big the planet is unless they know the actual size of the star. computer models give a very good estimate but in science, real measurements are best.

kipping(睡觉,逃学) realized that if a 3 planet has a moon big enough for us to see (by also blocking starlight), then the planet-moon-star system could be measured in a way that lets us calculate exactly how large and massive all three bodies are.

"basically, we measure the orbits of the planet around the star and the moon around the planet. then through kepler's laws of motion, it's possible to calculate the mass of the star," explained kipping.

the process isn't easy and requires several steps. by measuring how the star's light dims when planet and moon transit, astronomers learn three key numbers: 1) the orbital periods of the moon and planet, 2) the size of their orbits relative to the star, and 3) the size of planet and moon relative to the star.

plugging those numbers into kepler's third law yields the 4 of the star and planet. since density is mass divided by volume, the relative 5 and relative sizes gives the relative masses. finally, scientists measure the star's wobble(摆动,摇晃) due to the planet's gravitational 6, known as the radial 7(径向速度) . combining the measured velocity with the relative masses, they can calculate the mass of the star directly.

"if there was no moon, this whole exercise would be impossible," stated kipping. "no moon means we can't work out the density of the planet, so the whole thing grinds to a halt(慢慢停止) ."

kipping hasn't put his method into practice yet, since no star is known to have both a planet and moon that transit. however, nasa's kepler spacecraft should discover several such systems.

"when they're found, we'll be ready to weigh them," said kipping.



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1 569155f16962e086bd7de77deceefcbd     
n.天文学者,天文学家( astronomer的名词复数 )
参考例句:
  • astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
  • astronomers used to ask why only saturn has rings. 天文学家们过去一直感到奇怪,为什么只有土星有光环。 来自《简明英汉词典》
2 mglzvt     
n.经过,运输;vt.穿越,旋转;vi.越过
参考例句:
  • his luggage was lost in transit.他的行李在运送中丢失。
  • the canal can transit a total of 50 ships daily.这条运河每天能通过50条船。
3 0d2b64f42b39f00330eeb628166d7138     
通过(transit的现在分词形式)
参考例句:
  • the effect of the transiting mechanic required reserve system vehicle is low. 准备金制度的传导机制的作用是很低的。
  • i was busy transiting to the telescope. 我正忙着旋转望远镜。
4 rodzz     
n.密集,密度,浓度
参考例句:
  • the population density of that country is 685 per square mile.那个国家的人口密度为每平方英里685人。
  • the region has a very high population density.该地区的人口密度很高。
5 eca5c1ea104bef3058e858fe084fb6d0     
密集( density的名词复数 ); 稠密; 密度(固体、液体或气体单位体积的质量); 密度(磁盘存贮数据的可用空间)
参考例句:
  • the range of densities of interest is about 3.5. 有用的密度范围为3.5左右。
  • densities presumably can be probed by radar. 利用雷达也许还能探测出气体的密度。
6 5kbzo     
v.用力拖(或拉);苦干;n.拖;苦干;拖船
参考例句:
  • we need to tug the car round to the front.我们需要把那辆车拉到前面。
  • the tug is towing three barges.那只拖船正拖着三只驳船。
7 rlyzx     
n.速度,速率
参考例句:
  • einstein's theory links energy with mass and velocity of light.爱因斯坦的理论把能量同质量和光速联系起来。
  • the velocity of light is about 300000 kilometres per second.光速约为每秒300000公里。
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