Читать книгу Exploring the Solar System - Peter Bond - Страница 65

1 1 Plasma – often described as the fourth state of matter (after solids, liquids, and gases) – is an almost completely ionized gas, in which atoms or molecules are converted into ions by the addition or removal of one or more electrons. The hot mixture comprises negatively charged electrons and positively charged protons derived from high‐speed collisions between ions. The electrons and protons neutralize each other, so there is no net charge.

2 2 The longest total eclipse of the 21stcentury, which took place over Asia on July 22, 2009, lasted a maximum of 6 minutes 39 seconds. This duration will not be exceeded until 2132.

3 3 An electron volt is a measure of energy. It is defined as the kinetic energy gained by an electron passing through a potential difference of one volt.

4 4 The black lines are sometimes called Fraunhofer lines after Joseph von Fraunhofer who, in 1814, invented the diffraction grating. Many years passed before Gustav Kirchhoff discovered the link between the spectral lines and the chemical composition of the Sun.

5 5 There are two other possible proton‐proton reactions which are not described here.

6 6 The coolest part of the Sun is in the lower chromosphere, about 500 km above the photosphere, where the temperature is about 4,370°C.

7 7 A coronagraph is an instrument that uses a disk to blot out the glare of the light from the Sun's disk.

8 8 These are generally known as magnetohydrodynamic waves. The most important types involved in coronal heating are magneto‐acoustic waves (sound waves that have been modified by the presence of a magnetic field) and Alfvén waves (similar to ULF radio waves that have been modified by interaction with plasma).

9 9 The waves are named after Hannes Alfvén, who received a Nobel Prize in 1942 for his work in this field.

10 10 The 11‐year sunspot cycle is actually half of a 22‐year cycle of solar activity in which the Sun's magnetic polarity reverses roughly every 11 years, then flips back after 22 years.

11 11 Direct, naked eye observation of the Sun is very dangerous and proper eye protection is essential.

12 12 As it expands and loses mass, the Sun's gravitational pull will decrease, causing the planets to move away from the Sun. Earth and Mars will probably escape being swallowed by the swelling star.