Last modified: Tuesday, July 1, 2003
Mars will double in brightness again during July
Mars will be the only bright planet that is easy to see in the evening sky during July. The fiery red-orange object appearing to hover motionless in the southeastern sky after midnight will probably provoke a rash of UFO reports.
Mars will double in brightness again during July, after doing the same last month, and it will grow dramatically in size as well. Observers with telescopes and a clear sky should be able to see considerable detail on the planet's surface, unless a Martian dust storm wipes out the view. Mars will become even bigger and brighter in August as we catch up with it in our smaller orbit.
The other four planets visible with the unaided eye will be clustered in pairs very low in the sky shortly after sunset and before dawn, out of sight for all but determined observers.
Jupiter will set about two hours after the sun at the beginning of July, but by month's end it will appear close to the west-northwestern horizon after sunset, following the sun down less than an hour later.
Mercury will do the opposite, climbing out of the solar glare in the last week of the month and becoming visible slightly to the upper right (north) of Jupiter by the evening of July 25. Jupiter will be four times brighter than Mercury, and you'll need binoculars and a clear view of the horizon to see both planets. On July 29 and 30, the star Regulus will be extremely close to Mercury, creating a cluster of three bright white objects near the horizon.
Venus and Saturn will be similarly close together and low in the east-northeast a half hour before sunrise early in July. As the days pass, Venus will rise closer and closer to the sun, eventually disappearing into the morning brightness.
Saturn will appear higher each day, however, and by the end of the month it will rise more than two hours before the sun.
Viewing information and graphics are available at http://www.space.com/spacewatch/.
The bright white star Vega in the constellation Lyra the Harp is part of a trio of conspicuous white stars called the Summer Triangle that crosses the sky every night during the warm months in the Northern Hemisphere. Vega is the first of them to rise in the east each night. The others are Altair in the constellation Aquila the Eagle to the south and Deneb in the constellation Cygnus the Swan to the north. When you are looking from Deneb to Altair, you are also looking at our home galaxy, the Milky Way, though it is obscured by city lights.
A delicate phenomenon of the twilight sky called noctilucent clouds is sometimes visible in the Northern Hemisphere during summer. These wispy clouds float about 50 miles above Earth's surface, where meteors appear. Noctilucent clouds form when water vapor condenses onto meteoric dust particles to form ice crystals, so they look somewhat like the common cirrus ice-crystal clouds that appear during the day. But noctilucent clouds are so thin that they are invisible in daylight. They become visible only when the sun is just below the horizon, either in the northwest after sunset or in the northeast before sunrise, when the background sky is dark enough but there is still some light. Look for delicate bluish-white veils above the place where the sun is below the horizon. They contrast sharply with regular clouds, which appear dark against the morning or evening twilight. Photographs of noctilucent clouds can be seen at http://cumulus.helsinki.fi/~tpnousia/nlcgal/nlcgal.html.
The Delta Aquarid shower will peak around the end of the month, with meteors visible before and after the peak as well. The new moon will not interfere, so viewing conditions should be ideal if the sky is clear. The meteors will appear to come from a point in the constellation Aquarius in the southern sky during the hours just before morning twilight, with perhaps as many as 20 meteors per hour at the peak on July 29.
Some other minor meteor showers also will be visible in a clear, dark sky during the last week of July, and there could be a few early arrivals from the major Perseid shower that will peak in August.
The moon will be at first quarter on July 7, full on July 13, at third quarter on July 21 and new on July 29.