OZONE / DNA the sun damages the DNA of the exposed skin cells. In response, the cells release enzymes that excise the damaged parts of the DNA and encourage the production of replacement DNA. Due to the increase in the incidence of skin cancer and the effects of ozone layer depletion, more attention is being placed on protecting the skin from the sun’s ultraviolet rays with broad spectrum sunscreens or clothing.- K M, @2 L4 _# p- G. N
neutron telescope; Q; ^# p7 o* L& G) I2 I3 [6 f2 D
It is a big tube made of some metal, which will absorb neutrons. Neutrons collide the metal to produce another kind of particle, which can be studied by scientists.. K) ~5 ^, R. ^
Venus is often referred to as the sister planet of the earth, because it is only slightly smaller in both size and mass. Several important differences, however, exist between the two planets.2 f' V) g0 d4 E1 I0 c) I
Galileo observed them systematically for several weeks before concluding that they had to be events taking place on the solar surface. The temperature of the spots is lower than that of the surrounding photosphere; thus the spots are darker. All but the smallest show a dark central portion (the umbra) with a lighter outer area (the penumbra). An 11-year cycle from one period ofmaximum activity to the next is usually observed. During each 11-year period sunspots appear first at higher latitudes and later at latitudes closer to the solar equator as the period progresses. The spots often form in pairs or groups. |
发表于 2012-8-14 23:06:24
