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EI2GYB > ASTRO 05.08.23 11:32l 106 Lines 7679 Bytes #999 (0) @ WW
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Subj: This Week's Sky at a Glance, July 21 - 30
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This Week's Sky at a Glance, July 21 - 30
By: Alan MacRobert July 21, 2023
FRIDAY, JULY 21
Ý In late twilight, look about a fist at arm's length above the Moon for Denebola, Beta Leonis. That's the tip of Leo's tail. Because this is late July, Leo is going goodbye.
SATURDAY, JULY 22
Ý A twilight challenge. Spot the crescent Moon in the west-southwest about 30 minutes after sunset. Look for Venus about three fists at arm's length to its lower right. Fainter Mercury, even fainter Regulus, and puny Mars form a straight diagonal line a little way above Venus. The line is about fist and a half long and runs from lower right to upper left.
SUNDAY, JULY 23
Ý To me, the thick waxing crescent is one of the most interesting phases for exploring the Moon's terminator with a telescope. And this evening, above or upper right of the Moon by a couple degrees is 3rd-magnitude Gamma Virginis (Porrima), a fine close telescopic double star for telescopes. Its components are 3.3 arcseconds apart this year, oriented almost north-south. They're both magnitude 3.5.
Ý It's late July. . . so can you catch the heliacal rising of Rigel and Orion's Belt - far out of season! - low in the brightening dawn? See the July Sky & Telescope, page 50.
MONDAY, JULY 24
Ý With the advance of summer the Sagittarius Teapot, in the south-southeast after dark now, is starting to tilt and pour from its spout to the right. The Teapot will tilt farther and farther to pour for the rest of the summer - or for much of the night if you stay out late.
TUESDAY, JULY 25
Ý First-quarter Moon (exact at 6:07 p.m. EDT, when the Moon is in afternoon view for North America). After dark, look for Spica a fist to the Moon's lower right. Much higher, about three fists upper right of the Moon shines bright Arcturus. A similar distance to the Moon's left is orange Antares in Scorpius.
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 JULY 26
Ý We're not yet 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, JULY 27
Ý This evening for North America, the waxing gibbous Moon shines just to the right of the head-of-Scorpius stars: a nearly vertical row of three. The brightest of these is the middle one, Delta Scorpii, just to the Moon's upper left, as shown below. Somewhat farther left is the orange-red supergiant Antares.
FRIDAY, JULY 28
Ý Now the Moon shines just a few degrees left of Antares through the evening, as shown above. But of course they're not the slightest bit close together. The Moon is 1.3 light-seconds from us. Antares, at a distance of about 550 light-years, is some 13 billion times farther away. Moreover, Antares is estimated to be almost 200,000 times larger 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. 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 around a bit to get it all.
SUNDAY, JULY 30
Ý Now the Moon is on the other edge of the Teapot: in its handle. Again, use binocs to pick the stars out of the moonlight if necessary.
This Week's Planet Roundup
Mercury is deep in the glow of sunset, in the vicinity of brighter Venus. Start looking for them about 20 minutes after sunset. Binoculars help.
Mercury is 10ø to Venus's right on July 21st. It moves to 6ø above Venus by the 28th. During that time Mercury fades slightly, from magnitude -0.3 to 0.0.
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 (magnitude -4.5) is getting very low in bright twilight, more so every day. Use binoculars to look for it due west starting 15 or 20 minutes after sunset.
Get your telescope on Venus during late afternoon if you can, while it's higher in a clear blue sky. (Be careful not to sweep across the Sun by accident!) Venus is a tiny, thin white crescent, enlarging and thinning as it swings closer to Earth and ever closer to our line of sight to the Sun. From July 21st to 28th it expands from 46 to 51 arcseconds in diameter while waning from 15% to 9% sunlit. But really, by as late as the 28th it will be gone from sight altogether.
Mars (only magnitude +1.8!) glows weakly upper left of Venus and Regulus as twilight deepens. Mars and Venus are 9«ø apart on July 21st, and 12ø by the 25th. Good luck.
Don't confuse Mars with sparkly Regulus, magnitude +1.4, which is nearer to Venus.
Jupiter (magnitude -2.4, in Aries) rises around midnight or 1 a.m. 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, before the first glimmers of dawn.
Uranus, magnitude 5.8 in Aries, is high in the east by the beginning of dawn. It's about 10ø lower left of Jupiter.
Neptune, magnitude 7.9 at the Aquarius-Pisces border, rises after dark and is high in the south-southeast 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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