THIS WEEK'S SKY AT A GLANCE, APRIL 10 – 18

A week ago Venus was smack on the edge of the Pleiades. Now the Pleiades have sunk down 6° away from it.
Friday, April 10
■ Venus continues to blaze in the west during and after twilight, as shown above.
■ Right after dark, Orion is still well up in the southwest in his spring orientation: striding down to the right, with his three-star belt horizontal. The belt points left toward Sirius and right toward Aldebaran and, farther on, Venus .
Look at Orion's two shoulders. Orange Betelgeuse is obviously brighter than Bellatrix to its lower right, now that Betelgeuse has been recovering its brightness for the last two months. In early February it bottomed out at magnitude 1.6, as dim as Bellatrix. As of April 5th Betelgeuse was back up to 0.7, almost normal. It's now obviously closer in brightness to Rigel (0.2) than it is to Bellatrix.
The asteroid 3 Juno, just past opposition and visible in a small telescope at magnitude 9.5, is passing a mere ½° southwest of the 3rd-magnitude star Delta Virginis. You've got about two hours of dark sky this evening between the end of twilight and moonrise. Use the finder chart in the April Sky & Telescope, page 50. (There, Juno's position ticks are for 0:00 UT on the dates indicated, which in North America falls on the afternoon or evening of the previous date.) The chart continues to track Juno for the rest of the month, as it fades to magnitude 10.
■ Algol and its constellation Perseus, off to the right of Venus, sink ever lower in the northwest after dark as the season advances. For skywatchers in western North America, Algol goes through one of its eclipses this evening. It should be at its minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 9:14 p.m. Pacific Daylight Time.
Saturday, April 11
■ As stars are coming out an hour or so after sunset, look southwest for Sirius, the departing Winter Star. It's the brightest point in the sky after dazzling Venus in the west.
Now turn and look due east for Arcturus, the arriving Spring Star. It's shining at the same height as Sirius (depending on the time and your latitude). These are the two brightest stars in view right now. But Capella is a very close runner-up to Arcturus! Spot it high in the northwest, about two fists at arm's length to the upper right of Venus.
Sunday, April 12
■ Right after dark this week, look high in the southwest and find Procyon high above brighter Sirius. Look upper left of Procyon by 15° (about a fist and a half at arm's length) for the dim head of Hydra, the enormous Sea Serpent. His head is a group of 3rd- and 4th-magnitude stars about the size of your thumb at arm's length.
About a fist and a half lower left of Hydra's head shines Alphard, his 2nd-magnitude orange heart. The rest of Hydra zigzags (faintly) from Alphard all the way down to the southeast horizon.
Monday, April 13
■ With the evening sky moonless, make an evening of it exploring the dim constellation Sextans, south of Regulus, using your telescope and the Deep-Sky Wonders column, chart, and drawings in the April Sky & Telescope, page 54. The brightest of Sextans' deep-sky objects is the edge-on lenticular galaxy NGC 3115. At 9th magnitude, it's a fairly easy catch in a 4- or 6-inch telescope under a good sky  if you know how to use the chart with your telescope!

And at low power with a wide field, can you catch Rinnan's Run? It's a remarkably straight "star chain" of 8th- and 9th-magnitude stars, 2.3° long and detectable with large binoculars in a good dark sky.
Tuesday, April 14
■ Algol, in Perseus to the right of Venus, should be at minimum brightness for a couple hours centered on 9:03 p.m. Eastern Daylight Time.
■  Last-quarter Moon (exact at 6:56 p.m. EDT). The half-lit Moon doesn't rise tonight until around 3 a.m. daylight-saving time. Just before the beginning of dawn Wednesday, the Moon is high in the south-southeast. Saturn is about 3° below it (for the Americas), and Jupiter and Mars flank them.

You may be familiar with telescopic view of the waxing Moon in the evening. But how about the Moon's waning phases in the pre-dawn hours, when its opposite hemisphere is lit and the Sun casts shadows of familiar features in the opposite direction? The Straight Wall, for instance, is now bright instead of dark.
Wednesday, April 15
■  This evening Venus forms a perfect isosceles triangle (two sides equal) with Aldebaran to its lower left and the Pleiades to its lower right.
Thursday, April 16
■  Right after dark, the Sickle of Leo stands vertically upright high due south. Its bottom star is Regulus, Leo's brightest. Leo himself is walking horizontally westward. The Sickle forms his front leg, chest, mane, and part of his head.
Friday, April 17
By April 17th, the Pleiades sink 11° away from Venus.
By April 17th, the Pleiades have sunk 11° away from Venus. Soon they'll be down out of sight.
■ Venus today is passing 10° north (upper right) of Aldebaran, as shown above.
■ Bright Arcturus is climbing high in the east these evenings. Equally bright Capella is descending high in the northwest, to the upper right of Venus. Arcturus and Capella stand at exactly the same height above your horizon at some particular moment between about 9:00 and 10:30 p.m. daylight-saving time, depending mostly on how far east or west you live in your time zone.
How accurately can you time this event for your location? Like everything constellation-related, it happens 4 minutes earlier each night.
Saturday, April 18
■ This is the time of year when, as the last of twilight fades away, the dim Little Dipper extends straight to the right from Polaris. High above the end-stars of the Little Dipper's bowl, you'll find the end-stars of the Big Dipper's bowl.

THIS WEEK'S PLANET ROUNDUP

Mercury is buried in the glow of sunrise.
Venus (magnitude –4.6, in north-central Taurus) is the dazzling white "Evening Star" high in the west during and after dusk. Venus doesn't set in the west-northwest until about 2½ hours after complete dark. Look below it for the Pleiades.
In a telescope, Venus has enlarged to 30 arcseconds in diameter while waning in phase to become a thick crescent, 40% sunlit. Venus will continue to enlarge and wane, becoming a dramatically thin crescent low in twilight in late May.
Mars, Jupiter, and Saturn (magnitudes, +0.6, – 2.2, and +0.6, respectively) are lined up in the southeast before and during early dawn, as shown below. Each morning Mars moves a little farther away from the other two.
Uranus is hidden in the afterglow of sunset.
Neptune is hidden in the sunrise.
By April 11th, Mars has pulled away from Saturn so that the three form an almost evenly spaced line.
Jupiter, Saturn, and Mars form an almost straight line in early dawn as the week begins. But day by day, Mars moves farther away to the lower left.
Watch the waning Moon pass under them on the mornings of the 14th, 15th, and 16th.

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) is Universal Time (UT, UTC, GMT, or Z time) minus 4 hours.

Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.
This is an outdoor nature hobby. 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 guide to astronomy.
Jumbo Pocket Sky Atlas cover
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown above is the Jumbo Edition for easier reading in the night. Sample chart.
Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.
Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, are the even larger Interstellarum atlas (stars to magnitude 9.5) and Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.
You'll also want a good deep-sky guidebook, such as Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer's Guide by Kepple and Sanner.
Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). And 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."


No comments:

Powered by Blogger.