Our local star

The sun is the glorious body that dominates the solar system and the origin and destiny of the earth as well as our daily lives are closely connected with solar phenomena. The astronomer has another reason for studying the sun closely, for it is in many ways a typical star. The properties of the sun that we can observe by virtue of its relative closeness, then, are interesting not only in themselves but also because they provide information about stars in general that would otherwise be inaccessible.

The sun is so large that 1,300,000 earths would fit into it. Like all other astronomical bodies, it is rotating, though with the peculiarity that its period of rotation is shorter near its equator than near its poles. Although conditions on the sun are very different from those on the earth, the basic matter of the two bodies appears to be the same¹. Even the relative amounts of different elements are similar, except for a vastly greater abundance of the lightest elements, hydrogen and helium, on the sun. At the low temperatures prevailing on the earth, most of the elements have combined to form compounds; in the hot sun the elements are usually present as individual atoms, most of them ionized.

The surface temperature of the sun is about 5,700 ⁰C. At this temperature all matter is gaseous, which means that the surface of the sun is a glowing gas envelope. Above the surface is a rapidly thinning atmosphere that consists principally of hydrogen, helium, and calcium. From this atmosphere great, flamelike prominences sometimes extend out into space, much like sheets of gas standing on their sides. During a total eclipse of the sun, when the moon obscures the sun’s disk completely, a wide halo of pearly light can be seen around the dark moon. This halo, or corona, may extend out as much as a solar diameter and seems to have² a great number of fine lines extending outward from the sun immersed in its general luminosity. The corona consists of ionized atoms and electrons in extremely rapid motion.

Although the corona that we can see is relatively near the sun, indirect evidence indicates that, in very diffuse form, it also pervades much of the region between earth and sun. Most authorities even regard the sun’s atmosphere as extending well beyond the earth’s – a radical change indeed from the older idea that interplanetary space is an all but total vacuum. The outward flow of ions and electrons in this atmosphere constitutes the solar wind which has been detected by rocket-borne instruments.

Notes:

1. the basic matter appears to be … – очевидно, основное вещество является

2. this halo seems to have … – по-видимому, гало обладает …

Ex. 1. Complete the following sentences.

1. The sun is …

2. The main reason for studying the sun is …

3. The properties of the sun are interesting because …

4. The sun and the earth differ in …

5. The rotation of the sun is unusual because …

Ex. 2. Here are the answers. What are the questions?

1. The astronomer studies the sun because it is in many ways a typical star.

2. Like all other astronomical bodies the sun is rotating.

3. Hydrogen and helium are extremely abundant in the sun.

4. The surface temperature of the sun is about 5,700⁰ C.

5. The sun’s surface is a glowing gas envelope.

6. The sun’s atmosphere consists principally of hydrogen, helium and calcium.

Ex. 3. Explain and expand on the following.

1. We are totally dependent on our local star.

2. Solar prominences.

3. The corona of the sun.

4. The solar wind.