Skywatch Line for Friday, April 3, through Sunday, April 5, written by Sam Salem

This is Dudley Observatory’s Skywatch Line for Friday, April 3, through Sunday, April 5, written by Sam Salem.

On Friday, Sun rises at 6:34am and sets at 7:24pm; Moon sets at 6:53am and rises at 9:28pm.

On Friday evening, the waning gibbous Moon floats near Zubenelgenubi, the brightest star in the constellation Libra the Scales. Spica, the brightest star in the constellation Virgo the Maiden sits nearby.

On Friday, Mercury reaches greatest western elongation. Mercury glows low in the glare of sunrise at magnitude 0.4. Try to spot it some 4° above the eastern horizon about half an hour before the Sun rises. Mercury is in the constellation Aquarius and tracking eastward, or prograde, against the background stars. Through a telescope, the planet’s disk spans 8” on the sky. It is roughly half-lit. Mercury remains at roughly the same altitude above the horizon, while Mars and Saturn slowly rise to meet it in the morning sky.

Venus, at magnitude –3.9, glows low in the evening twilight. Look for it due west, forty minutes after sunset. It will still be about a fist at arm’s length above horizontal. It sets at twilight’s end.

Jupiter, at magnitude -2.2, is bright and nearly overhead when you face south as the stars come out. Jupiter soon shifts to the very high southwest, then moves lower later in the evening. It sets around 3 am on the west-northwest horizon. In a telescope Jupiter is 40 arcseconds wide. It’s shrinking and fading as Earth pulls farther ahead of it in our faster orbit around the Sun.

On Friday, Callisto, Jupiter’s slowest-moving large satellite, casts its tiny black shadow onto Jupiter’s face from 9:14 pm to 1:32 am. Callisto itself is a good two or three Jupiter-diameters off to Jupiter’s west. Jupiter’s Great Red Spot should transit the planet’s meridian around 9:48 pm.

Uranus, at magnitude 5.8, sits in the constellation Taurus the bull, 4° south of the Pleiades. The Pleiades are still high in the west at nightfall. Uranus is some 30° high in the west at the end of twilight. At high power in a telescope, it’s a tiny non-stellar dot, 3.5 arcseconds wide. Use a finder chart to identify it among similar-looking faint stars.

Arcturus, the bright Spring Star climbs in the east, shortly after the end of twilight. It stands just as high as Sirius, the brighter Winter Star descending in the southwest.

These are the two brightest stars in the sky at the time.