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Northern Hemisphere gazer's guide.

April 1: First quarter moon. The two bright stars to the left and above the moon are Pollux (the brighter) and Castor, the ''Twin'' stars of Gemini.

Venus is at its greatest distance to the right of the sun (greatest westerly elongation). In this position, the planet is ordinarily in the best position to be seen as a morning star, since it rises well before the sun does. But this is an unfavorable morning elongation for Venus because it remains quite low until it disappears in the brightening dawn.

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April 3-4: The bright star near the moon is Regulus, in Leo. The moon moves from west to east past Regulus on the morning of the 4th.

April 5: Mars is nearest the earth during this cycle of configurations. The planet was in opposition from the sun on March 31. Now at its brightest, Mars dims significantly during the next two months as its distance from earth rapidly increases. The distance from earth to Mars today is about 95,010,000 kilometers. Its distance from earth can be as little as 56 million kilometers when an opposition occurs when Mars is at or near perihelion (closest to the sun).

April 6-7: The bright gibbous moon (almost full) passes from right to left above Mars. Conjunction of moon and planet occurs at about 8 a.m., Eastern standard time on the 7th.

April 8: Full moon. The two bright objects nearest the moon tonight are Saturn (above) and Spica (below), the brightest star of Virgo. Mars is to the right and Jupiter to the left, both much brighter than Saturn and Spica.

April 9: Saturn is at opposition from the sun, rising at sundown and setting at sunrise. On successive nights after this, the planet will be above the horizon at sunset, but not at sunrise. This makes it an ''evening'' star, tehnically, even though it is still about equally prominent at dawn as it is at dusk.

April 11: Mercury is in superior conjunction, in line with but beyond the sun as observed from earth. The planet now moves from west to east (right to left) past the sun, taking it into the evening sky.

April 11-12: The bright reddish star south of the moon on these nights is Antares, in Scorpius. The moon moves eastward past Antares on the morning of the 12th.

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April 13: The moon is at apogee, farthest from earth.

April 14: The waning gibbous moon is in Sagittarius.

April 16: Last quarter moon.

April 20: The very bright object you can see near the slim waning crescent moon this morning is Venus. The moon is near the vernal equinox today, the point where the earth's orbital and equatorial planes meet in the sky, where the sun is located when spring begins in the Northern Hemisphere.

April 22: The Lyrid meteor shower reaches maximum this morning. Though relatively sparse (15 meteors per hour) and not noted for bright objects, the phase of the moon is favorable. There will be no moonlight during the after-midnight hours when meteor hunting is best.

April 23: New moon.

April 25: The moon is at perigee, nearest to earth. Communities that shift their clocks to daylight time advance one hour this morning. Nothing to do with perigee, of course. Just happens to be the fourth Sunday.

April 25-26: You may see the very young crescent moon in the evening twilight as soon as the 25th, with the reddish star Aldebaran, in Taurus, to its left. The crescent should be easily visible on the 26th, with Aldebaran more distant to its right.

April 26: Jupiter is at opposition from the sun and enters the evening sky, the third of the three bright planets in our nighttime sky to do so within the past few weeks.

April 30: First quarter moon. The star nearby is Regulus, in Leo, and the moon passes it during the daytime on the 1st. The moon also passed Regulus on April 4, a bit more than 27 days ago, but it was at first-quarter phase on April 1, more than 29 days ago. Why the difference?

All month: The sky full of morning planets from last month fell apart in April. The process actually began on the last day of March, when Mars moved into the evening sky. Then in April, Saturn, Mercury, Pluto, and Jupiter follow suit. Whereas all the planets were morning stars in March, by the end of April we have only Venus, Uranus, and Neptune.

Mars, Jupiter, Saturn continue to present an imposing alignment of bright objects in Virgo, near its brightest star Spica. Shifting into the evening sky, they are better, if anything, because they are visible virtually all night long throughout April.

Don't fail to look for them on the 7th, 8th and 9th, when the moon is near them. And if you watch them regularly, note how their positions change among them and relative to Spica. It is relatively rare to see all these bright superior planets (outside earth's orbit) moving retrograde at the same time. With bright Spica among them as a ''fixed'' star guide, the movements of the planets are exceptionally easy to follow.

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