AURORA WATCH: High-latitude sky watchers, be alert for auroras. Earth is entering a solar wind stream that could spark geomagnetic storms tonight: gallery. AT THE EDGE OF SPACE: Yes, noctilucent clouds really do hover "at the edge of space." Consider this photo taken on July 22nd by astronauts onboard the International Space Station: The electric-blue band, a noctilucent cloud, lies approximately 83 km (51 miles) above Earth's surface. The sky at that altitude is space-black. It is the realm of meteors, high-energy auroras, and tiny crystals of ice that glow blue when struck by sunlight. Noctilucent clouds (NLCs) are made of those crystals; how they form in the extremely-dry upper reaches of Earth's atmosphere is a mystery. The space station was located some 320 km (200 miles) above Mongolia at the time of the display. Astronauts pointed their camera out a north-looking window where the midnight sun illuminated the clouds. The black expanse of Earth at the base of the snapshot is Russia. The view from the ISS is stunning, but space travel is not required to see NLCs. These mostly-polar clouds have been sighted in recent years from Earth's surface as far south as Oregon, Washington, Iran and Turkey. Browse the gallery for observing tips. LUNAR X: Last night, August 8th, a luminous X appeared on the Moon. "It was easily visible through both a 16-inch reflecting telescope and a 4-inch refractor," reports Kevin Jung of Lowell, Michigan. "I put my camera on the 16-inch at prime focus to capture this image." Jung witnessed the "Lunar X." Once a month when the sun rises over Crater Werner in the Moon's southern hemisphere, sunlight floods the region's high terrain and makes a luminous criss-cross shape. The effect lasts only about two hours so careful timing and a little luck is required to catch it. "The sky was clear and the Moon was just past first quarter by a few hours," says Jung. Perfect. "Observing the 'X' has little or no scientific value. It is a trick of the light. But the effect is striking, and it is exciting to rediscover each month," writes David Chapman in "A Fleeting Vision near Crater Werner" (Journal of the Royal Astronomical Society of Canada, Vol. 101, Issue 2, p.51). The next apparition: September 7th at 0945 UT. Mark your calendar with an X. more images: from Mark Seibold of Portland, Oregon; from David Thomas of Lynchburg, Virginia; from John Scarfone of Clifton, Virginia; Solar Eclipse Photo Gallery [interactive eclipse map] |