This Week's Sky at a Glance for August 20 – 28

This Week's Sky at a Glance

Some daily events in the changing sky for August 20 – 28.

by Alan M. MacRobert

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The path of Psyche's star-shadow across Earth on the morning of August 21st.

Steve Preston

Friday, August 20

Good asteroid occultation: in the early-morning hours of Saturday, an 8.4-magnitude star near Aldebaran (in the loose star cluster NGC 1647) will be occulted for up to 10 seconds by the large asteroid 16 Psyche, magnitude 11.1, along a wide path from Texas to Virginia. Maps, times, and finder charts.

The asteroid-occultation community eagerly seeks accurate timings of such events, especially by video, which is more precise than eyeball timings. Read up on timing methods. If you get involved in this addictive pursuit, join the busy discussion at the occultation Yahoo Group.

Saturday, August 21

The bright eclipsing variable star Algol should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 10:18 p.m. EDT — when it will be visible from the East Coast low in the northeastern sky. Algol takes several additional hours to fade and to rebrighten. Use our comparison-star chart.

Sunday, August 22

Vega passes nearest the zenith soon after dark at this time of year. Whenever you see Vega there, it means Altair is high in the southeast with its little companion Tarazed almost directly above it. And the Sagittarius Teapot is at its best lower in the south.

Monday, August 23

Arcturus is the brightest star in the west as the stars come out (high above the place where Venus sinks and sets in twilight). At about the same height in the northwest, look for the Big Dipper now turning right-side up. Equally high in the northeast, W-shaped Cassiopeia is climbing.

Tuesday, August 24

Full Moon (exact at 1:05 p.m. EDT).

Wednesday, August 25

One of the first deep-sky objects of summer that new telescope owners learn to find is the Ring Nebula, M57, because its location is so well marked in Lyra. But have you looked in on Lyra's other Messier object, the globular cluster M56? See the chart with Gary Seronik's Binocular Highlight article in the August Sky & Telescope, page 45.

Although they look close together, Jupiter is 1,500 times farther from us than the Moon is when they pass on the 26th and 27th.

Sky & Telescope diagram

Thursday, August 26

The "star" below the Moon late this evening is Jupiter, as shown at right.

Friday, August 27

Low in the west-southwest in twilight, Venus forms the bottom of a flat, symmetrical triangle with much fainter Mars and Spica a little higher. Binoculars help.

Jupiter shines to the right of the Moon once they rise after dark, as shown here.

Saturday, August 28

The Venus-Spica-Mars triangle low in the west-southwest in twilight is distorting now, as Spica moves closer to Venus.

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This Week's Planet Roundup

Mercury is hidden in the glare of the Sun.

Venus, though bright at magnitude –4.4, is getting low in the west-southwest during twilight. It sets by dark.

Mars, vastly dimmer at magnitude +1.5, is a little to Venus's upper right. Look also for similar Spica farther to Venus's upper left for most of the week. Saturn has moved far off to Venus's right or lower right. Bring binoculars for all three of these faint objects.

By August 13th, Jupiter's Oval BA (Red Spot Junior) had nearly caught up with the Great Red Spot and was about to pass it. Also note the ghostly tan and blue-gray signs of the broad South Equatorial Belt hidden under white clouds. These traces now include the outline of the Red Spot Hollow just below the spot. South is up.

Christopher Go took this stacked-video image at 18:03 UT Aug. 13, 2010.

Christopher Go

Jupiter (magnitude –2.8, in Pisces) rises in late twilight and is well up in the east-southeast before midnight. It's highest in the south around 2 or 3 a.m. daylight saving time — the brightest starlike point in the morning sky.

Jupiter's Great Red Spot is near System II longitude 150°. Assuming it stays there, here's a list to print out of all the Great Red Spot's predicted transit times for the rest of 2010.

Uranus (magnitude 5.8, in Pisces) is about 2° west of Jupiter. In a telescope Uranus is only 3.7 arcseconds wide, compared to Jupiter's unusually wide 48″.

Neptune (magnitude 7.8, at the Aquarius-Capricornus border) is up high by mid- to late evening. See our finder charts for Uranus and Neptune in 2010.

Pluto (magnitude 14, in northwestern Sagittarius) is highest in the south right after dusk, but the bright Moon interferes this week. (See our Pluto finder charts in the July Sky & Telescope, page 60.)

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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 (also known as UT, UTC, or GMT) minus 4 hours.