Last modified: Wednesday, June 29, 2005
Fireworks in space on the Fourth of July
BLOOMINGTON, Ind. -- This year there will be more than the usual fireworks on the Fourth of July.
NASA's Deep Impact probe is on target to smash into the icy nucleus of Comet Tempel 1 on July 4 (the night of July 3-4 in the time zones of North America). The resulting crater and cloud of debris will provide a better understanding of the interior of a comet, and the impact may brighten the comet dramatically.
A telescope will be needed to witness the event, but NASA has produced an animation of what the encounter and impact might look like up close:
http://www.nasa.gov/mov/117656main_Maas_DI_Short_320x240.mov (short version)
http://www.nasa.gov/mov/117657main_Maas_DI_Long_320.240.mov (long version).
There will be a live Webcast from Kitt Peak National Observatory in Arizona, beginning about an hour before the impact and continuing for about 45 minutes afterward. It will show the collision as it appears from Earth, 83 million miles away, so the comet will only be a bright spot of light on the screen. The Webcast will be available at http://www.noao.edu/news/deep-impact, which is currently showing the comet as it moves through space.
The cosmic collision is scheduled at 5:52 Universal Time on July 4, which is 10:52 p.m. Pacific Daylight Time on July 3. The timing favors mostly the countries of the Pacific Ocean, since that side of the world will be facing the comet at the time of impact. At that moment, the comet will be well placed in a dark sky for the western United States, especially the Southwest. But for much of the eastern United States and Canada, as well as for all other parts of the world, the comet will be below the horizon.
No one is certain what we will see, or whether the comet's nucleus will remain intact. Comets that flare up as a result of splitting apart can remain brighter for months or years.
All five of the planets that can be seen with the unaided eye will be visible during July, some of them much more visible than others.
Four of the five will appear at dusk early in the month. The fifth, Mars, will be glowing orange in the southeastern sky before dawn.
Venus and Mercury will perform a stately dance low in the west-northwest 45 minutes before sunset during the first part of the month. They will appear side-by-side on July 1, with Venus much brighter and Mercury a fainter dot to the left (south) of Venus. Binoculars may be needed to see both of them in the glow of twilight. The bright star to their upper left will be Regulus in the constellation Leo the Lion.
During the next two weeks, Mercury will drift away from Venus toward the horizon, disappearing from view after midmonth. Venus will gradually rise toward Jupiter as a beautiful "evening star" that often prompts UFO calls to police departments.
Saturn will be barely visible above the western horizon at the start of the month. After the first week, it will be overwhelmed by the solar glare as it passes behind the sun. Saturn will reappear in the morning sky in late August.
Far to the upper left (south) of Venus will be Jupiter, blazing high in the southwest and very easy to spot. After Venus sets, Jupiter will be the brightest point of light in the sky.
The moon will be new on July 6, at first quarter on July 14, full on July 21 and at third quarter on July 28.