My first Magazine Sky & Telescope - 04.2019

The splendor-ringed world is in eastern Sagittarius, its brightness increasing from magnitude +0.6 to +0.5 during the month. Saturn begins April less than 26° from Jupiter, but as the latter starts retrograding away from Saturn the gap increases to almost 27° by month’s end. Actually, on April 29th in the Ameri- cas, Saturn begins its own retrograde motion. Since Saturn’s movement is much slower than Jupiter’s, however, the two will continue to separate from each other for several more months. At the end of April, Saturn reaches the meridian just a few minutes before sunrise. Morning twilight is the best time to point a telescope at Saturn this month, catching its disk growing slightly to 17″ and its rings continuing to be highly tilted and lovely. DAWN Venus and Mercury both rise during morning twilight and form a fascinat- ing pair this month — but unfortu- nately they are quite low in the east- southeast for observers at mid-northern latitudes. Mercury, speciﬁ cally, is never higher than 5° at civil twilight. Venus comes up ﬁ rst, a beacon of magnitude –3.9 appearing less than 12″ across and about 88% illuminated by month’s end. As April opens, Mercury rises about Mars December solstice Uranus Jupiter Sun Neptune Saturn an hour before the Sun (but shines at only magnitude +0.9 — use binoculars!) and as the month ends only about 40 minutes before the Sun (though by then Mercury has brightened to –0.3). Mer- cury reaches a greatest western elonga- tion of 28° from the Sun on April 11th. What’s perhaps most interesting about Mercury and Venus this month is their separation. On April 1st these two planets are about 10° apart. The gap between them shrinks pretty rapidly, but Mercury falls back towards the Sun before Venus can catch it and have a conjunction in right ascension. Instead, 45 minutes before sunrise Saturn Moon Apr 25 Antares C a t ’s Eyes SAGITTARIUS SCORPIUS Looking South-Southwest Venus The curved arrows show each planet’s movement during April. The outer planets don’t change position enough in a month to notice at this scale. 45 minutes before sunrise Moon Apr 22 Mercury ORBITS OF THE PLANETS Dawn, April 24 – 25 Moon Apr 23 Earth June solstice Dawn, April 22 – 23 Jupiter Sept. equinox March equinox Looking South what happens is a “quasi-conjunction” — a pairing of less than 5° separation that occurs without a true conjunction. In this case, the quasi-conjunction (the ﬁrst between planets in almost three years) occurs on April 16th when Mer- cury and Venus are about 4 1 / 3 ° apart. Neptune is just emerging from the solar glare at dawn in April, but if you have a telescope, clear skies, and a sharp eye you may catch the 8th-magnitude world a little more than 1 / 3 ° north of Venus on the morning of April 10th in the Americas. Uranus is at conjunction with the Sun on April 22nd and is therefore lost in the solar glare all month. MOON PASSAGES Moon Apr 24 The Moon is a very thin, waning cres- cent some 8° right of Venus on April 1st at dawn in the Americas. The waxing lunar crescent is far below Mars and the Pleiades on the evening of April 7th but forms a quite compact and almost equilateral triangle with them the next night. The Moon is 5° above Aldebaran on April 9th. The waxing gibbous Moon is 5° or 6° from Regulus on the night of April 14–15. The waning gibbous Moon is 1° from Jupiter on the morning of April 23rd and 2° lower right of Saturn on the morning of April 25th. ¢ Contributing Editor FRED SCHAAF had the 10-mile-wide asteroid 7065 Fred- schaaf named after him in 2016. sk yandtele scope.com • A PR I L 2 019 47

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