Last modified: Tuesday, July 2, 2002
Venus and Regulus meet in the west
Venus will be the only bright planet that is easy to see in the evening sky during July. The other four planets visible with the unaided eye will be clustered in pairs very low in the western and eastern skies shortly before sunset and dawn, out of sight for all but determined observers.
Venus will continue to dominate the sky after sunset, appearing in the west as darkness falls and setting about two hours after the sun. By the second week of the month, Venus will be near the bright white star Regulus in the constellation Leo the Lion. Venus and Regulus will be closest on the evenings of July 9 and 10. They will be joined by the crescent moon on July 12 and 13.
Jupiter will appear very low in the west-northwest and set less than an hour after the sun in early July. Each night it will sink even lower, and before midmonth it will be lost in the solar glare.
Mars will be only slightly higher than Jupiter at the start of the month and too faint to be seen without a telescope in the bright afterglow of sunset. Jupiter and Mars will be closest about a half hour after sunset on July 2 and 3. Mars will continue to linger just above the horizon after Jupiter has disappeared.
Mercury and Saturn will be correspondingly low in the east-northeast before sunrise during July. Both will be much dimmer than Jupiter but much brighter than Mars. After being extremely close on the morning of July 2, they will separate as Mercury drops quickly back into the solar glare and Saturn moves higher. By month's end, Saturn will rise more than three hours before the sun and be visible low in the east if you have a clear view of the horizon.
Viewing information and graphics are available at http://www.space.com/spacewatch/.
A delicate phenomenon of the twilight sky called noctilucent clouds is visible in the Northern Hemisphere during June and July. 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, appearing only when the background sky is dark enough. Look for delicate bluish-white veils above the place where the sun is slightly below the horizon. They contrast sharply with regular clouds, which appear dark against the morning or evening twilight. Noctilucent clouds become visible only in the summer when the sun is just below the horizon, either in the northwest after sunset or in the northeast before sunrise.
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 moon will be just a few days past full, so only bright fireballs are likely to show, and patience will be needed to see them. 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 third quarter on July 2, new on July 10, at first quarter on July 17 and full on July 24.