Science

The sky this week for July 13 to 22

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Friday, July 13

The Southern Delta Aquariid meteor shower continues to ramp up this week. The shower won’t peak until the end of July, but you should see some of its meteors in the hours before dawn. The best time to look is between 3 and 4 a.m. local daylight time, just before twilight begins. Viewing conditions will be great this week because the Moon will be gone from the predawn sky. Unfortunately, our satellite will show a fat gibbous phase at the shower’s peak the night of July 29/30. To tell a Southern Delta Aquariid meteor from a random dust particle burning up in Earth’s atmosphere, trace the streak of light’s path backward. A shower meteor will appear to originate from the constellation Aquarius the Water-bearer.

The Moon reaches perigee, the closest point in its orbit around Earth, at 4:25 a.m. EDT. It then lies 222,097 miles (357,431 kilometers) away from us. Since perigee arrives less than six hours after yesterday evening’s New Moon, residents of coastal areas can expect to see tides rise higher than normal for the next couple of days.

Saturday, July 14

Look for a slender crescent Moon 2° above Mercury in this evening’s sky. A half-hour after the Sun goes down, the Moon hangs 9° (the approximate width of your closed fist when held at arm’s length) above the western horizon. Through binoculars, both objects should stand out against the colorful twilight background. A telescope reveals the magnitude 0.5 planet’s disk, which spans 8″ and shows a crescent phase.

Sunday, July 15

The Moon moves approximately 13° eastward relative to the starry background every 24 hours, and that motion carries it near Venus this evening. The crescent Moon appears just 2° to the right of the brilliant planet, which gleams at magnitude –4.2. The stunning duo stands 15° high in the west 45 minutes after sunset. This conjunction provides a nice photo opportunity. If you shoot the twilight scene before 9:30 p.m. local daylight time, you’ll also capture Regulus to the lower right and Mercury even closer to the horizon. When viewed through a telescope, Venus appears 18″ across and nearly two-thirds lit.

Monday, July 16

Observers with telescopes should get their first good views of Comet 21P/Giacobini-Zinner before dawn in mid-July. The comet currently glows at 10th magnitude against the photogenic northern Milky Way of southern Cepheus. This morning, Giacobini-Zinner lies midway between 3rd-magnitude Zeta (ζ) Cephei and 4th-magnitude Delta (δ) Cep.

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