This Week's Sky at a Glance July 16 – 24

This Week's Sky at a Glance
Some daily events in the changing sky for July 16 – 24.
by Alan M. MacRobert
Forthe last few days, the waxing crescent Moon has marched along wellsouth of the ecliptic. Mercury, Venus, Mars, and Saturn lie much closerto the ecliptic (the plane of the solar system projected onto Earth'ssky).
Sky & Telescope diagram
Friday, July 16
Look for Saturn and Mars to the right of the Moon at nightfall, as shown above.
Saturday, July 17
Face east as the starscome out, and look very high; the brightest star there is Vega. Denebis the brightest star to Vega's lower left, by 2 or 3 fist-widths atarm's length. Farther to Vega's lower right is Altair (with littleTarazed just above it). Vega, Deneb, and Altair form the big SummerTriangle.
Sunday, July 18
First-quarter Moon (exact at 6:11 a.m. Eastern Daylight Time).
Monday, July 19
Bright Vega passes highestoverhead around midnight daylight saving time this week, depending onyour longitude within your time zone. (How accurately can you time whenVega does this?) How close to the zenith Vega passes depends on your latitude. Vega goes exactly overhead if you're at north latitude 39°: Washington DC, St. Louis, Kansas City, Lake Tahoe.
Tuesday, July 20
The brightest star in thewest after dark is Arcturus, slowly moving lower now as summeradvances. To its right in the northwest, the Big Dipper is swingingdown into proper dipping position.
Thewaxing gibbous Moon crosses upper Scorpius on Tuesday and Wednesday.These scenes are drawn for the middle of North America. Europeanobservers: move each Moon symbol a quarter of the way toward the onefor the previous date. For clarity, the Moon is shown three timesactual size.
Sky & Telescope diagram
Wednesday, July 21
After dark, look to the right of the waxing gibbous Moon for Antares and other stars of upper Scorpius, as shown here.
Thursday, July 22
Jupiter's Great Red Spotshould cross the planet's central meridian (the line down the center ofJupiter's disk from pole to pole) around 1:10 a.m. Friday morningEastern Daylight Time, when Jupiter will be well up in the sky forobservers the U.S. eastern time zone. See ourfull list of all Red Spot transit times for the rest of 2010.
Friday, July 23
Saturn's wild, weird moonTitan is west of Saturn this evening. A small telescope will show it(at 9th magnitude). Follow Titan as it swings back and forth in orbitaround Saturn every 16 days. Saturn's rings, meanwhile, still appearvery narrow, but they've widened a trace in the last several weeks to3° from edge on — even as the entire Saturnian system has beenshrinking into the distance.
Saturday, July 24
A line from Deneb through Altair (the longest side of the Summer Triangle) points down nearly to the Moon this evening.