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Pacific Ocean

Planet Earth: The Pacific Ocean rules our water-covered world.

Astronomy news for the week starting Friday, April 5, 2002.

Prepared by Jim Kaler.

The entire week sees the waning of the crescent Moon, none of the quarters passed, as last quarter took place on Thursday, April 4, and new Moon will not occur until Friday, April 12. The quartering of the Moon's orbit, plus the moving "seven bodies of the sky" (the Sun, Moon, and 5 naked-eye planets) surely led to the concept of the week. The time-period of the month comes from the 29.5 day period of the phases. The months of both the Moslem and Jewish calendars adhere to the 29-30 day month, while the civil calendar (from old Rome) stretches the months to fit the year. The Moon also gives us the date for Easter, now past, which takes place on the first Sunday following the first full Moon past the time of solar passage across the vernal equinox.

As the crescent Moon descends the early morning sky, it passes four degrees south of the two outer planets, Uranus and Neptune, which (in Capricornus) have now well-cleared the Sun, the Moon gliding by Neptune on Saturday the 6th, Uranus on Sunday the 7th. While the two planets are still more or less in the same direction, Uranus, to the east of Neptune, is ever so slowly pulling away from its sister. Given the long orbital periods of the two (84 years for Uranus, 165 for Neptune), we will not see them in this configuration again for another 170 years.

Uranus and Neptune are hard to see, though Uranus is in fact just visible to the naked eye. In contrast, two brilliant planets dominate western evening skies. Venus is unmistakable in bright twilight, while much higher Jupiter in Gemini lasts until after midnight. Between the two is fading Mars and bright Saturn, which are slowly approaching each other in the constellation Taurus, Mars situated south of the Pleiades, Saturn north of the Hyades and Aldebaran. The shorter period of Jupiter (12 years) and Saturn (29.5 years) allow them to rendezvous much more frequently, the two planets passing each other every 20 years. A passing does take place this week as little Mercury hides behind the Sun, the planet in superior conjunction on Sunday the 7th.

North of Jupiter find Gemini's pair of bright stars, Castor and Pollux, which look back at us like a pair of celestial eyes. The most northerly constellation of the zodiac, Gemini holds the summer solstice, which is now rather well-marked by Jupiter (the solstice 8 degrees to the west of the bright planet). To the east of Gemini lies dim Cancer (the Crab), marked best by the fuzzy patch that binoculars reveal as a fine cluster, the Praesepe or Beehive. Farther to the east find that true harbinger of spring, Leo the Lion, whose front end is graced by the first magnitude star Regulus. More easterly yet, toward the southeast at 9 PM or so, see Spica in Virgo climbing the sky. Between the two stars is the autumnal equinox, where the Sun will be on the first day of autumn.

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