ABOUT THE MOON: The moon is Earth's only natural satellite, a cold, dry orb whose surface is studded with craters and strewn with rocks and dust. The moon's gravitational force is only 17 percent of the Earth's gravity. For example, a 100 pound (45 kg) person would weigh just 17 pounds (7.6 kg) on the Moon. The temperature on the Moon ranges from daytime highs of about 265F (130C) to nighttime lows of about -170F (-110C). The moon has no atmosphere. On the moon, the sky always appears dark, even on the bright side (because there is no atmosphere). Also, since sound waves travel through air, the moon is silent; there can be no sound transmission on the moon. The phases of the moon are caused by the relative positions of the earth, sun, and moon. The moon goes around the earth, on average, in 27 days, 7 hours, and 43 minutes. The sun always illuminates the half of the moon facing the sun (except during lunar eclipses, when the moon passes through the earth's shadow). When the sun and moon are on opposite sides of the earth, the moon appears "full" to us, a bright, round disk. When the moon is between the earth and the sun, it appears dark, a "new" moon. In between, the moon's illuminated surface appears to grow (wax) to full, then decreases (wane) to the next new moon.
WHAT IS THE SOLAR WIND? Flowing outward from the Sun's extremely hot corona, the solar wind is a stream of charged particles traveling in all directions at incredibly high speeds. As these changes speed toward the Earth, they interact with other charged particles and can create phenomena such as the northern lights and geomagnetic storms, which can damage spacecraft, including communications satellites.