快猫短视频

THE ghostly glow of the new Moon can tell us about Earth鈥檚 weather, and may
explain how the Sun鈥檚 solar cycle affects the Earth鈥檚 climate.

On a clear, dark night, the dim face of a new or crescent Moon is lit by
Earthshine鈥攍ight from the Sun that has been reflected off the Earth. This
allows it to be seen against the night sky.

Now Philip Goode and his colleagues at the New Jersey Institute of Technology
have measured Earthshine by looking at new and crescent Moons between 1998 and
2000. 鈥淲hen the Moon is new, the Earth is full in the Moon鈥檚 sky,鈥� he says. This
allows you to measure the Earthshine from half of the Earth at once, as opposed
to satellite measurements which have to be pieced together using complex
computer algorithms.

The team worked out that Earth reflects about a third of the light from the
Sun and that this varies by as much as 10 per cent with the seasons. By
comparing their recent data with pilot observations taken in 1994, the team
found that Earth鈥檚 average reflectivity has fallen by 2 per cent since then,
suggesting a decrease in cloud cover.

Goode says this might be explained by the fact that 1994 was the last 鈥渟olar
minimum鈥�. The Sun鈥檚 magnetic activity follows an 11-year cycle, with a weaker
magnetic field at solar minimum. When the field is weaker, more galactic cosmic
rays can enter the Sun-Earth system. These rays could be partially responsible
for seeding clouds, says Goode.