This Week's Sky at a Glance

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

by Alan M. MacRobert

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

Steve Preston

Friday, August 20

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

The asteroid-occultation community eagerly seeks accurate timings ofsuch events, especially by video, which is more precise than eyeballtimings. 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 eclipsingvariable star Algol should be in one of its periodic dimmings, magnitude3.4 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 thenortheastern sky. Algol takes several additional hours to fade and torebrighten. Use our comparison-star chart.

Sunday, August 22

Vega passes nearest thezenith soon after dark at this time of year. Whenever you see Vegathere, it means Altair is high in the southeast with its littlecompanion Tarazed almost directly above it. And the Sagittarius Teapotis at its best lower in the south.

Monday, August 23

Arcturus is the brighteststar in the west as the stars come out (high above the place whereVenus sinks and sets in twilight). At about the same height in thenorthwest, look for the Big Dipper now turning right-side up. Equallyhigh 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 firstdeep-sky objects of summer that new telescope owners learn to find isthe Ring Nebula, M57, because its location is so well marked in Lyra.But have you looked in on Lyra's other Messier object, the globularcluster M56? See the chart with Gary Seronik's Binocular Highlightarticle 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-southwestin twilight, Venus forms the bottom of a flat, symmetrical trianglewith 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.

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'supper right. Look also for similar Spica farther to Venus's upper leftfor 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.

ByAugust 13th, Jupiter's Oval BA (Red Spot Junior) had nearly caught upwith the Great Red Spot and was about to pass it. Also note the ghostlytan and blue-gray signs of the broad South Equatorial Belt hidden underwhite clouds. These traces now include the outline of the Red SpotHollow 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 iswell up in the east-southeast before midnight. It's highest in thesouth around 2 or 3 a.m. daylight saving time — the brightest starlikepoint 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. Ina telescope Uranus is only 3.7 arcseconds wide, compared to Jupiter'sunusually 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 inthe south right after dusk, but the bright Moon interferes this week.(See our Pluto finder charts in the July Sky & Telescope, page 60.)

All descriptions that relate to your horizon or zenith — includingthe words up, down, right, and left — are written for the world'smid-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 4hours.

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This Week's Sky at a Glance

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