Some daily events in the changing sky for April 17 25.
Comet Yi-SWAN isn't much at magnitude 8½, but it's far north, crossing from Cassiopeia into Perseus (near the Double Cluster) this week. It's low in the northwest right after dark, and low in the northeast right before the first light of dawn. The farther north you are the better. See our AstroAlert with the comet's positions for plotting on your star atlas.
Friday, April 17
Saturday, April 18
Sunday, April 19
Monday, April 20
Tuesday, April 21
Wednesday, April 22
Thursday, April 23
Friday, April 24
Saturday, April 25
Will this sighting set your personal young-Moon record? The crescent will be only about 21 hours from new at viewing time from the East Coast of North America, and 24 hours from new as seen from the West Coast. Have you ever seen a crescent that thin? (Calculate from the exact time of new Moon under Friday above.)
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 each issue of Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).
Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts; the standards are Sky Atlas 2000.0 or the smaller Pocket Sky Atlas) and good deep-sky guidebooks (such as Sky Atlas 2000.0 Companion by Strong and Sinnott, the even more detailed Night Sky Observer's Guide by Kepple and Sanner, or the classic Burnham's Celestial Handbook). Read how to use them effectively.
Can a computerized telescope take their place? As Terence Dickinson and Alan Dyer say in their 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 and a curious mind." Without these, they note, "the sky never becomes a friendly place."
More beginners' tips: "How to Start Right in Astronomy".
This Week's Planet Roundup
Mercury (about magnitude 0.5) is having its best evening apparition of the year. Look for it low in the west about an hour after sunset. As the sky gets darker, the Pleiades glimmer into view above it. Watch the Pleiades sink lower toward Mercury every day.
Venus (magnitude 4.7) shines low in the dawn. Look for it above the horizon due east about 60 to 40 minutes before sunrise. (Don't confuse it with Jupiter, which is much higher and far to the right in the southeast.)
In a telescope, Venus is a thickening and shrinking crescent. The best telescopic views come in full morning daylight, when Venus is higher in steadier air.
Mars (only magnitude +1.2) is very low in the sunrise glow. It's 5° or 6° to the lower right of Venus early in the week, and about 4° directly below Venus late in the week. Use big binoculars. Good luck.
Jupiter (magnitude 2.2, in Capricornus) shines in the southeast before and during dawn.
Saturn (magnitude +0.7, in Leo) shines high in the southeast at dusk and highest in the south around 9 p.m. Regulus, a little less bright, sparkles 16° (roughly one and a half fist-widths at arm's length) to Saturn's upper right in early evening, and directly to its right later.
In a telescope, Saturn's rings are 4° from edge on. They'll close to become exactly edge-on next September 4th, when, unfortunately, Saturn will be out of sight practically in conjunction with the Sun.
Uranus (6th magnitude) is hidden low in the sunrise glow, in the background of Venus and Mars.
Neptune (8th magnitude) is also in the glow of dawn, in the background of Jupiter.
Pluto (14th magnitude, in northwestern Sagittarius) is in the south-southeast before the first light of dawn.
All descriptions that relate to your horizon or zenith 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 (known as UT, UTC, or GMT) minus 4 hours.
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