Earthshine on the Moon
The amount of sunlight that is reflected back into space due to clouds, bodies of water, snow cover, etc., is known as albedo (cloud cover is by far the most influential). Albedo is a major factor in determining the global temperature. Measuring albedo has proven difficult in the past, because the calculations were based on knowledge of the total energy provided by the sun, then subtracting out the energy accounted for by the Earth's temperature. Basically, it's the difference between how hot the Earth would be if it absorbed all of the sun's energy. A novel new method of measuring albedo has been devised that looks at the amount of earthshine illuminating the night side of the crescent moon. It is much more accurate, and does not depend on calculations involving the Earth's temperature. After 270 days of measurement, a research team found that the earth is roughly 10% more reflective than the average during April and May. This means the Earth is significantly cloudier during those months. NASA's best computer models predicted only a 5% increase.