This Week's Sky at a Glance
Some daily celestial sights for April 13 21
Saturday, April 14
Sunday, April 15
Monday, April 16
Tuesday, April 17
Wednesday, April 18
Thursday, April 19
Friday, April 20
Saturday, April 21
Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.
For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).
Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts effectively.
You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the classic if dated Burnham's Celestial Handbook.
Can a computerized telescope replace charts? I don't think so not for beginners, anyway, and especially not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability). As Terence Dickinson and Alan Dyer say in their invaluable Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."
This Week's Planet Roundup
Mercury (magnitude +0.4) is deep in the glow of sunrise. It's having a very poor dawn apparition just above the eastern horizon.
Venus (magnitude 4.6; in Taurus) is shining the highest and brightest it ever appears in the evening sky during its 8-year cycle of repeating apparitions. Venus comes into easy view high in the west soon after sunset. It doesn't set in the northwest until around 11 or even midnight daylight saving time (depending on where you live). You can see Venus through the clear blue sky of day if your eye lands right on it; look for it 44° (4 or 5 fist-widths at arm's length) to the Sun's celestial east-northeast.
Look high to Venus's upper right at dusk for Capella, to its lower left for Aldebaran, and to its lower right for the Pleiades. Far below Venus in twilight is Jupiter.
The best time to examine Venus in a telescope is late afternoon or around sunset. It's now a thick crescent 30 arcseconds tall and 40% sunlit, waning and enlarging week by week as it swings toward Earth.
Mars (magnitude 0.4) shines fire-orange in Leo. Regulus is 4° to Mars's right in early evening, and fainter Gamma Leonis is 7° above it. Look for them high in the south.
Mars in a telescope is a small 11.4 arcseconds wide, fading and shrinking as Earth pulls ahead of it in our faster, inside-track orbit around the Sun.
Jupiter (magnitude 2.0) is sinking ever lower toward the sunset, far below Venus. It's rounding toward the far side of the Sun, which is why a telescope shows it a disappointingly small 33 arcseconds wide. In addition, Jupiter appears increasingly fuzzy at its ever-lower altitude.
Saturn (magnitude +0.2, in Virgo) is at opposition this week, on April 15th. It rises in twilight and glows highest in the south around 1 a.m. Shining 5° to its right is Spica: fainter, bluer, and twinklier.
Keep careful watch on Saturn and its rings in a telescope. With Saturn at or near near opposition, notice the Seeliger effect: a temporary brightening of the rings with respect to the globe. This happens because the solid particles making up the rings backscatter sunlight (reflect it back in the direction it came from) more effectively than the planet's cloudtops do. Compare how the rings and globe look now with with how they look a week or more past opposition.
Uranus is hidden low in the dawn.
Neptune (magnitude 7.9, in Aquarius) is barely emerging into view low in the east-southeast before dawn's first light.
All descriptions that relate to your horizon including the words up, down, right, and left are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America. Eastern Daylight Time (EDT) equals Universal Time (also known as UT, UTC, or GMT) minus 4 hours.
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