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EI2GYB > ASTRO 05.08.23 10:32l 112 Lines 9928 Bytes #999 (0) @ WW
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Subj: This Week's Sky at a Glance, July 28 - August 6
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This Week's Sky at a Glance, July 28 - August 6
By: Alan MacRobert July 28, 2023
Comet 12P/Pons-Brooks in outburst. It was supposed to be 16th or 17th magnitude now, but on July 20th this distant comet brightened 100 times to mag 11 or 12. It's high overhead crossing the head of Draco these evenings, spreading and becoming more diffuse. You may need an 8- or 10-inch scope. More at Bob King's See Comet 12P/Pons-Brooks in Outburst, with pix and finder charts. This comet has a long history of outbursts, so more could happen.
This is a preview. Even if the comet returns to normal and stays there, in the course of its incoming orbit it should reach 4th or 5th magnitude in April 2024, when it will hang low in the west near Jupiter around the end of evening twilight.
FRIDAY, JULY 28
Ý This evening the Moon shines just a few degrees left of Antares, as shown below. But of course they're not the slightest bit close together. The Moon is 1.3 light-seconds from us. Antares is some 13 billion times farther away, at a distance of about 550 light-years. Moreover, Antares is estimated to be almost 200,000 times larger than the Moon in diameter. Nowhere in human experience but astronomy are things so different than they appear.
SATURDAY, JULY 29
Ý The Moon hangs just off the spout of the Sagittarius Teapot this evening (as shown above) like a giant, dazzling drop that the Teapot spit out. Binoculars may help you pick out the Teapot stars through the moonlight. Remember that the Teapot is about twice as wide as a typical binocular's field of view, so expect to sweep a bit to find it all.
SUNDAY, JULY 30
Ý Now the Moon is on the other edge of the Teapot, an overwhelming ornament on its handle. Again, use binocs to help pick the stars out of the moonlight.
MONDAY, JULY 31
Ý The two brightest stars of summer are Vega, overhead shortly after nightfall, and Arcturus, shining in the west. Draw a line down from Vega to Arcturus. A third of the way down, the line crosses the dim Keystone of Hercules. Two thirds of the way down the line crosses the dim semicircle of Corona Borealis with its one modestly bright star, Alphecca or Gemma.
Vega and the Keystone's star closest to it form an equilateral triangle with Eltanin to their north, the nose of Draco the Dragon. Eltanin is the brightest star of Draco's quadrilateral head; he's eyeing Vega.
TUESDAY, AUGUST 1
Ý Full Moon (exact at 2:23 p.m.) in southern Capricornus. As twilight fades, look for Altair very high over it. Once the Moon is nicely up, look for Saturn two fists at arm's length to its left.
Ý As summer progresses, Arcturus always moves down the western side of the evening sky. It forms the bottom point of the Kite of Boötes. The Kite, rather narrow, extends upper right from Arcturus by 23ø, about two fists at arm's length.
The top of the kite is bent slightly down. The kite's short tail currently hangs nearly straight down from Arcturus.
WEDNESDAY, AUGUST 2
Ý The Moon, now just a day and a fraction past full, rises in late twilight. This evening look for Saturn about 6ø to the Moon's left or upper left. They'll draw closer through the night as they wheel across the sky together.
Ý We're not quite halfway through summer, but already W-shaped Cassiopeia, a high constellation of fall and winter evenings, is climbing up in the north-northeast as evening grows late. And the Great Square of Pegasus, emblem of fall, comes up to balance on one corner just over the eastern horizon.
THURSDAY, AUGUST 3
Ý The waning gibbous Moon rises around the very end of twilight. Saturn glows to its upper right. Farther to the Moon's upper left, the Great Square of Pegasus is balancing on one corner. The Square's top-right edge points down lower right toward the Moon.
FRIDAY, AUGUST 4
Ý Fourth star of the Summer Triangle? The next-brightest star near the Summer Triangle, if you'd like to turn it into a quadrilateral, is Rasalhague, the head of Ophiuchus, magnitude 2.1. Face south soon after dark. You'll find Rasalhague about equally far to the right of Altair and lower right of Vega. Altair is currently the Summer Triangle's lowest star. Vega, nearly overhead, is its brightest.
SATURDAY, AUGUST 5
Ý Bright Vega passes closest to overhead around 10 or 11 p.m., depending on how far east or west you live in your time zone. How closely it misses your zenith depends on how far north or south you are. It passes right through your zenith if you're at latitude 39ø north (Washington DC, Cincinnati, Kansas City, Lake Tahoe). How closely can you judge this just by looking?
Deneb crosses closest to the zenith two hours after Vega. To see Deneb exactly straight up, you need to be at latitude 45ø north: for example Portland (either Oregon or Maine), Minneapolis, Montreal, southern France, northern Italy, southern Ukraine.
SUNDAY, AUGUST 6
Ý The Big Dipper hangs diagonally in the northwest after dark. From its midpoint, look to the right to find Polaris (not very bright) glimmering due north as always.
Polaris is the end of the Little Dipper's handle. The only other Little Dipper stars that are even modestly bright are the two forming the outer end of its bowl: 2nd-magnitude Kochab and 3rd-magnitude Pherkad. On August evenings you'll find them to Polaris's upper left (by about a fist and a half). They're called the Guardians of the Pole, since they ceaselessly circle around Polaris throughout the night and throughout the year.
Ý Seeing any early Perseid meteors yet? A few Perseids trickle in starting in late July, then they build for a couple of days toward their peak, which this year is predicted for the night of August 12-13. The sky then will be moonless for perfect meteor-watching conditions. The weak, long-lasting Delta Aquariid shower is also somewhat active throughout this time. For both, the later in the night the more meteors you'll see. More details to come next week!
This Week's Planet Roundup
Mercury and Venus are very deep in the glow of sunset. Early in the week, use binoculars about 15 or 20 minutes after sunset to start looking for them low above the horizon due west. Venus is about magnitude -4.2. Mercury is only about 1/50 as bright, fading slightly this week from magnitude 0.0 to +0.2, but at least it's higher.
On July 28th Mercury is 6ø above Venus. It moves farther away, to 15ø upper left of Venus by August 4th, but by then Venus is just plain gone from post-sunset view.
Bonus: on July 28th Mercury is passing very close by fainter Regulus, magnitude +1.4. They'll be only 0.1ø or 0.2ø apart as seen in twilight from the longitudes of the Americas. Use binoculars or better, a telescope. In a telescope Mercury will be very tiny (6.2 arcseconds diameter) and gibbous.
Venus in a telescope is entering its most extreme crescent phase, when its hair-thin cusps start extending around the planet's circumference toward forming a complete ring. The time to examine Venus telescopically now is in the blue sky of afternoon, when it and the Sun are still high. But when looking for Venus take care not to accidentally sweep up the Sun! Keep your eye safe by setting up your scope at a spot where the Sun has just sunk behind a solid, level obstruction, such as the roofline of a house.
For more about observing this most interesting and challenging Venus phase, see Bob King's thorough View the Thin Crescent of Venus, including daylight finding instructions.
Mars is also nearby! But it's only magnitude +1.8. Look for it 11ø upper left of Mercury on July 28th, closing to 7ø upper left of Mercury by August 4th. Good luck.
Jupiter (magnitude -2.4, in Aries) rises around midnight or a little after in the east-northeast. By the beginning of dawn it shines very high toward the southeast.
Saturn (magnitude +0.7, in dim Aquarius) rises in late twilight. It's highest in the south, and sharpest and steadiest in a telescope, in the couple hours before dawn.
Uranus, magnitude 5.8 in Aries, is nice and high by the beginning of dawn, about 9ø left of Jupiter.
Neptune, magnitude 7.9 at the Aquarius-Pisces border, rises after dark and is high in the south before dawn begins, about 2oø east of Saturn.
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 and graphics that also depend on longitude (mainly Moon positions) are for North America.
Eastern Daylight Time (EDT) is Universal Time minus 4 hours. UT is sometimes called UTC, GMT, or Z time.
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