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Astronomy Picture of the Day


Photo of the Week.. Planet Earth: Like Venus and Mars, Earth is covered with volcanos, this one Osorno in Chile.

Astronomy news for the week starting Friday, August 30, 2002.

The Moon begins the week in its last quarter, the phase reached on Friday, August 30, shortly before moonrise in the Americas. It thereafter wanes through its crescent phase, appearing ever-closer to the eastern horizon at dawn. As it orbits Earth, the Moon can be found close to and to the northwest of Saturn the morning of Sunday, September 1, and well to the northeast of the ringed planet the following day, Saturn now rising in Taurus shortly after midnight, consistent with its proximity to the third quarter Moon. The morning of Wednesday, the 4th, the Moon (which will be rather well north of the ecliptic) will pass north of the giant planet Jupiter, which now rises in Cancer about 3:30 AM, Jupiter pulling steadily farther from more slowly moving Saturn.

The inner planets have events of their own. The night of Friday, August 30, Venus, brilliant in western evening twilight, makes a close pass to the south of the first magnitude star Spica in Virgo. Venus's low position and the brightness contrast between the two will make the conjunction somewhat difficult to see. Mercury then passes its greatest eastern elongation, when it is 27 degrees to the east of the Sun, on Sunday, September 1. Greatest elongations are clearly the best time to see the small planet. Unfortunately, this one is rather poor, as the ecliptic is so flat against the horizon in western evening skies that Mercury is very low and nearly lost in bright twilight.

As September arrives and the Sun approaches the autumnal equinox in Virgo, the shortening of the days is quickly accelerating and noticeable nearly from one day to the next. Depending somewhat on location, twilight is over and the sky fully dark by 9 PM, while morning twilight does not commence until almost 5 AM (all Daylight Time). The acceleration in times will continue until September 22, when autumn begins in the northern hemisphere. Scorpius is to late summer as Orion is to winter, the two opposite each other in the sky. Look to the south as evening begins to see bright Antares and, if you are far enough south, Scorpius's curving tail. Both constellations are filled with massive bright blue-white stars that are related to each other in loose unbound (that is, expanding), "associations." Most of these constellations' stars were born about the same time (on an astronomical time scale), and many will expire about the same time, the more massive ones (including Antares, which has evolved from a blue-white star into a huge red supergiant) will explode in grand supernovae.
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