With the fast development of astronomy, astronomers are eager to find a hint of the familiar: planets that resemble Earth. By pushing technology to the limits, astronomers are rapidly approaching the day when they can find another Earth.
The most direct approach is to take a picture of it with a telescope. However, a more effective way is to use “the Doppler technique”. This involves analyzing starlight for evidence that the star’s movement is affected by the gravitational pull of a planet. Nowadays, astronomers can tell when a planet is pulling its star by only one meter a second — about human walking speed. That’s enough to detect a giant planet in a big orbit, or a small planet if it’s close to its star.
Another approach is to watch a star for a slight dip in its brightness. This occurs when an orbiting planet passes in front of the star and blocks part of its light. At most, a tenth of all planetary systems are oriented so that these mini-eclipses (日食，月食) — called transits (凌日) — are visible from Earth. So, astronomers have to monitor a lot of stars to capture just a few transits.
The dream of astronomers is to discover a rocky planet roughly the size of Earth orbiting in a habitable zone, one that is neither too hot nor too cold to support life. If they succeed, they will have found what biologists believe could be a promising residence for life.
The best places to look may be dwarf stars. Smaller than the sun, dwarf stars are plentiful; seven of the ten stars nearest to Earth are dwarf stars. They also provide a steady supply of sunlight to any life-bearing planets within their habitable zone. Additionally, dwarf stars are dim, so the habitable zone lies closer in. If the planet is closer to the star, it’s easier for astronomers to detect a transit observation. A close-in planet also has a stronger pull on its star. That makes it easier to detect with the Doppler method.
【小题1】According to paragraph two, astronomers analyze starlight with the aim of finding ________.| A．where we can detect a giant orbit |
| B．why a small planet is close to its stars |
| C．whether the motion of the stars is changed |
| D．how strong the power of the gravitational pull is |
| A．Transits last a very short period of time. |
| B．Most planetary systems don’t have transits. |
| C．Transits only occur for a small number of stars. |
| D．No more than 10% planetary systems have visible transits from Earth. |
| A．dwarf stars are limited in number |
| B．their planets are close to the Earth |
| C．the closeness of the habitable zone to dwarf stars aids detection |
| D．the brightness of dwarf stars to Earth improves their visibility |
| A．Confident. | B．Suspicious. | C．Ambiguous. | D．Unconcerned. |
