Friday, April 14
Although the calendar says it is spring, the so-called Winter Hexagon remains prominent on April evenings. One of the sky’s largest asterisms — a recognizable pattern of stars separate from a constellation’s form — the hexagon stands out in the western sky after darkness falls. To trace this asterism, start with southern Orion’s luminary, Rigel. From there, the hexagon makes a clockwise loop. The second stop is brilliant Sirius in Canis Major. Next, pick up Procyon in the faint constellation Canis Minor, then the twins Castor and Pollux in Gemini, followed by Capella in Auriga, Aldebaran in Taurus, and finally back to Rigel.
Uranus is in conjunction with the Sun at 2 a.m. EDT. From our earthly perspective, this means the distant planet lies behind the Sun and so is out of sight. Uranus will return to view in the morning sky in late May.
Saturday, April 15
After passing between the Sun and Earth only three weeks ago, Venus already appears conspicuous in the predawn sky. It rises some 90 minutes before our star and climbs 10° above the eastern horizon 30 minutes before sunrise. The planet shines so brightly, at magnitude –4.7, that it shows up easily in the brightening twilight. A telescope will deliver spectacular views of the inner world’s 49"-diameter disk, which appears just 13 percent lit.
The Moon reaches apogee, the farthest point in its orbit around Earth, at 6:05 a.m. EDT. It then lies 251,950 miles (405,475 kilometers) from Earth’s center.
Sunday, April 16
For those who like to observe during the quiet predawn hours, Saturn offers a visual treat this week. The ringed planet rises before 1 a.m. local daylight time and climbs some 30° high in the south by the time morning twilight begins. It shines at magnitude 0.3 against the backdrop of northwestern Sagittarius, where it appears nearly stationary relative to the background stars. Take a look at Saturn 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, the planet shows a 17"-diameter disk surrounded by a stunning ring system that spans 40" and tilts 26° to our line of sight. And as a bonus, this morning the waning gibbous Moon appears near Saturn. The two approach each other as morning progresses; the Moon will pass 3° north of the planet at 2 p.m. EDT.