This Week's Sky at a Glance July 23 – 31

易工 2010-07-26

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This Week's Sky at a Glance

Some daily events in the changing sky for July 23 – 31.

by Alan M. MacRobert

Four planets shine in the western twilight. One dazzles; the others appear tiny by comparison. Watch them changing positions day by day! This is their arrangement at week's end. (The visibility of faint objects in bright twilight is exaggerated here.)

Sky & Telescope diagram

Friday, July 23

Saturn's wild, weird moon Titan is at western elongation from Saturn this evening. Most amateur telescopes will show it (at 9th magnitude). Follow Titan as it swings back and forth in orbit around Saturn every 16 days!

Saturday, July 24

A line drawn from Deneb, high in the east, through Altair, not quite as high in the southeast, points down nearly to the Moon this evening.

Jupiter's Great Red Spot transits Jupiter's central meridian around 2:48 a.m Sunday morning Eastern Daylight Time; 11:48 p.m. Saturday evening Pacific Daylight Time. See our list of all the Great Red Spot's predicted transit times, good worldwide, for the rest of 2010.

Sunday, July 25

Full Moon (exact at 9:37 p.m. EDT).

Monday, July 26

As the stars begin coming out in the evening this week, Arcturus shines high in the west, far to the upper left of bright Venus. Watch the Big Dipper glimmer into view equally high in the northwest, far to Venus's upper right.

Tuesday, July 27

Regulus is now less than ½° upper right of brighter Mercury low in the sunset glow. Use binoculars to look for the two a half hour after sunset. They're well to the lower right of brighter Venus.

Wednesday, July 28

Big Hercules remains high in the evening sky. Maybe you're familiar with its globular star clusters M13 and M92. But what about its bright Turtle Nebula, NGC 6210, or the faint galaxy NGC 6269 amid a cluster of even fainter companions? See Ken Hewitt-White's "Going Deep" article and maps in the July Sky & Telescope, page 63.

Thursday, July 29

Mars is less than 2° below slightly brighter Saturn at dusk, as shown at right.

Friday, July 30

Mars is still less than 2° below Saturn at dusk.

Jupiter rises roughly 6° lower right of the waning crescent Moon around 11 p.m. daylight-saving time (for skywatchers in North America).

Saturday, July 31

Saturn and Mars remain close together upper left of Venus at dusk, as shown at the top of this page. Use binoculars to try for Mercury and especially Regulus much farther to Venus's lower right.