题目内容
The temperature of the Sun is over 5,000 degrees Fahrenheit at the surface, but it rises to perhaps more than 16 million degrees at the center. The Sun is so much hotter than the Earth that matter can exist only as a gas, except at the core. In the core of the Sun, the pressures are so great against the gases that, despite the high temperature, there may be a small solid core. However, no one really knows, since the center of the Sun can never be directly observed. Solar astronomers do know that the Sun is divided into five layers or zones. Starting at the outside and going down into the Sun, the zones are the corona, chromospheres, photo-sphere, convection zone, and finally the core. The first three zones are regarded as the Sun’s atmosphere. But since the Sun has no solid surface, it is hard to tell where the atmosphere ends and the main body of the Sun begins. The Sun’s outermost layer begins about 10,000 miles above the visible surface and goes outward for millions of miles. This is the only part of the Sun that can be seen during an eclipse such as the one in February 1979. At any other time, the corona can be seen only when special instruments are used on cameras and telescopes to keep out the glare of the Sun’s rays. The corona is a brilliant, pearly white, filmy light, about as bright as the full Moon. Its beautiful rays are a sensational sight during an eclipse. The corona’s rays flash out in a brilliant fan that has wispy spike-like rays near the Sun’s north and south poles. The corona is thickest at the Sun’s equator. The corona rays are made up of gases streaming outward at tremendous speeds and reaching a temperature of more that 2 million degrees Fahrenheit. The rays of gas thin out as they reach the space around the planets. By the time the Sun’s corona rays reach the Earth, they are weak and invisible. The temperature of the Sun at the center is ______.
查看答案
搜索结果不匹配？点我反馈
更多问题
The basic flag of the United States is one of the world’s oldest national flags. Only the basic flags of Austria, Denmark, Great Britain, the Netherlands, Sweden, and Switzerland are older. During the discovery and settlement of what is now the United States, the flags of various European nations were flown over the land, as symbols of possession. Later, in the Colonial and Revolutionary War periods, flags representing famous persons, places, and events were flown in the American Colonies. The first official flag of the United States was created by Congress on June 14, 1777. It consisted of 13 alternate red and white stripes and 13 white stars in a field of blue, representing the 13 colonies that had declared their independence in 1776. Congress adopted a new flag of 15 stars and 15 stripes in 1795, to give representation to the two new states admitted into the Union, Vermont and Kentucky. By 1817, there were 20 states in the Union, and it became apparent that adding one stripe for each new state would destroy the shape of the flag. As a result, Congress in 1818 restored the original design of 13 stripes and provided that each state was to be represented by one star. In 1912 President William H. Taft made the first official provision for the arrangement of the stars. He ordered that there be six even rows of eight stars each. Previously the arrangement of the stars had been left to the flag-maker’s fancy. The evolution of the Stars and Stripes reflects the growth of the United States. After the admission of Hawaii into the Union in 1959, the flag was officially changed for the 26th time since its creation. There are many government flags flown in the United States in addition to the national flag. Among them are the president’s and vice president’s flags and those of the federal departments and some federal agencies. Each state in the Union has an official flag. The United States Navy uses special flags for signaling. Before the War of Independence, the flags of various European nations flown over the land were symbols of ______.
下列关于曲普瑞林的药理作用描述错误的是：
有关前列腺素E1的描述，正确的是：
排卵后形成的黄体可以分泌哪种激素
微信支付 
支付宝支付