Monday, April 3
First Quarter Moon arrives at 2:39 p.m. EDT. You can find the half-lit orb high in the southwest as darkness falls; it doesn’t set until about 2:30 a.m. local daylight time tomorrow morning. The Moon currently lies in south-central Gemini, between 10° and 15° southwest of the Twins’ brightest stars, Castor and Pollux.
Tuesday, April 4
The Big Dipper’s familiar shape rides high in the northeast on April evenings. The spring sky’s finest binocular double star marks the bend of the Dipper’s handle. Mizar shines at 2nd magnitude, some six times brighter than its 4th-magnitude companion, Alcor. Even though these two are not physically related, they make a fine sight through binoculars. (People with good eyesight often can split the pair without optical aid.) A small telescope reveals Mizar itself as double — and these components do orbit each other.
Wednesday, April 5
Saturn rises shortly after 1 a.m. local daylight time and climbs some 25° high in the south by the time morning twilight begins. The magnitude 0.4 ringed planet lies in the northwestern corner of Sagittarius the Archer, where it appears nearly stationary relative to the background stars. (Its slow eastward motion comes to a halt at 1 a.m. EDT on the 6th.) Take a look at the planet through binoculars and you’ll also see the open star clusters M21 and M23 as well as the spectacular Lagoon (M8) and Trifid (M20 ) nebulae less than 4° to its east. When viewed through a telescope, Saturn shows a 17"-diameter disk surrounded by a stunning ring system that spans 39" and tilts 26° to our line of sight.
Thursday, April 6
The variable star Algol in the constellation Perseus reaches minimum brightness at 10:58 p.m. EDT. Because Algol dips fairly low in the northwest during the evening hours, you’ll stand a better chance at seeing its relative dimness by comparing tonight’s view with one tomorrow night. This evening, Algol glows at magnitude 3.4, noticeably dimmer than Alcyone, the brightest member of the Pleiades star cluster (M45), which lies directly to Algol’s left. Tomorrow night, Algol will shine at magnitude 2.1, easily brighter than Alcyone and rivaling Perseus’ brightest star, magnitude 1.8 Mirfak.