This Week's Sky at a Glance for September 17 – 25.

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This Week's Sky at a Glance

Some daily events in the changing sky for September 17 – 25.

by Alan M. MacRobert

Watch the Moon at opposition pass Jupiter close to opposition. Before the 22nd, Jupiter will be there but not the Moon.Sky & Telescope diagramFriday, Sept. 17

  • Uranus is passing 0.8° north ofJupiter tonight and tomorrow night. Although Uranus is easily visible inbinoculars at magnitude 5.7, Jupiter outshines it by nearly 3,000 timesat magnitude –2.9. In fact, Uranus appears roughly as bright as one ofJupiter's four Galilean moons.

    Saturday, Sept. 18

  • You know summer is nearits end: as the stars come out, Cassiopeia in the northeast is alreadyas high as Big Dipper in the northwest!
  • Jupiter'sGreat Red Spot should cross Jupiter's central meridian (the imaginaryline down the center of the planet's disk from pole to pole) around11:05 p.m. Eastern Daylight Time. The "red" spot appears very paleorange-tan. It should be visible for about an hour before and after in agood 4-inch telescope if the atmospheric seeing is sharp and steady. Alight blue or green filter helps. (The Red Spot transits about every 9hours 56 minutes; for all of the Red Spot's central-meridian crossingtimes, good worldwide, use our Red Spot calculator or our list for the rest of this observing season.)

    Sunday, Sept. 19

  • Mira, the prototype redlong-period variable star in Cetus, has been visible to the unaided eyefor a couple weeks now; it's on its way up to a maximum predicted formid-October. Cetus is in good view in the east-southeast by about 11 ormidnight daylight saving time. See the comparison-star chart in theSeptember Sky & Telescope, page 58.

    Monday, Sept. 20

  • Jupiter's Great Red Spot should transit tonight around 12:43 a.m. EDT; 9:43 p.m. PDT.

    Tuesday, Sept. 21

  • The dim littleconstellation Scutum, high in the south after dark, lies in one of therichest parts of the Milky Way. It sports not only the famous open starcluster M11, but the nice globular cluster NGC 6712, the big, dimplanetary nebula IC 1295 — and the tiny planetary nebula Kohoutek 4-8 inthe same high-power view. Get out your OIII filter, and see KenHewitt-White's "Going Deep" article and chart in the September Sky & Telescope, page 64.

    Wednesday, Sept. 22

  • This evening Jupiter(and Uranus) are below the full Harvest Moon, as shown above. The Moonis exactly full at 5:17 a.m. Thursday morning EDT.
  • Autumn begins in the Northern Hemisphere, and spring in the SouthernHemisphere, at 11:09 p.m. EDT. This equinox marks when the Sun crossesthe equator heading south for the year. Day and night (if you includetwilight as night) are about equally long.

    Thursday, Sept. 23

  • Jupiter and Uranus are now left of the Moon during evening, as shown above.
  • Jupiter's Great Red Spot should transit around 10:12 p.m. EDT.

    Friday, Sept. 24

  • This is the time of yearwhen, after nightfall, the dim Little Dipper (you'll need a dark sky) isdumping water into the bowl of the Big Dipper far below it. Bailing outfor fall?

    Saturday, Sept. 25

  • Jupiter's Great Red Spot should transit around 11:50 p.m. EDT.

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