The April sky

Posted: Sunday, April 06, 2003

The planets this month are still Saturn and Jupiter, the latter dominant in the southern sky, the former being close to western horizon.

The first-quarter moon will be near Saturn on Monday, assisting in finding the ringed planet. Those rings are at their widest since 1987, having opened up for a grand view. Saturn also is at its closest to our sun during its 29-year orbit, making it extra large in a telescope or good binoculars (mount them on a tripod or hold them very steady with your elbows on a car roof). While you're at it, look for Jupiter's moons, as well.

The great constellations and stars of winter, from Orion to Taurus and Gemini, encompassing Jupiter and Saturn, are now quickly setting in the west. But look for Orion and the sky's brightest star, Sirius, on the southwest horizon.

Noteworthy among the spring constellations is especially Leo the lion, which follows Cancer where Jupiter resides and through which it moves this year (still close to the Beehive cluster). Spring is here as Leo appears high in the south.

Venus is now low in the east during dawn, while Mars becomes more of a late-night object, rising after 3 a.m. Despite it being so low, Venus still is easy to spot because it's so bright. Mars is red, the brightest object in its part of the sky (near Capricorn low in southeast during the wee hours) and is joined by our third-quarter moon around April 23.

But this month's favorite planet is actually the most elusive one.

April is the only month this year to spot all five naked-eye planets within the same night as Mercury reaches its greatest elongation from our sun on April 16. On that evening, it is trailing the sun by a full 20 degrees in the west during dusk.

One might want to enlist the help of the stars in Taurus, Saturn and the Pleiades and connect from there to the western horizon where Mercury is the only bright object.

A telescope shows half of Mercury illuminated (a first-quarter inner planet at that time) because at greatest elongation Mercury, the sun and Earth make up a right triangle that allows only half of Mercury's Earth-viewed side to reflect sunlight to Earth.

To top off Mercury's great showing, it would have gotten even better: the speedy planet transits across the sun's disk May 7 -- a great event if you were in Asia, Africa or Europe -- check the news on that day.

I will set up my telescope(s) on the Kenai beach access parking lot at the end of Spruce Drive on April 18 around 10 p.m. for a public evening -- weather permitting. Otherwise I'll try April 19, then 20.

Andy Veh is the physics and astronomy instructor at Kenai Peninsula College. This column will appear on the first Sunday of each month. He can be reached at aveh@uaa.alaska.edu.



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