This Week's Sky at a Glance for September 24 – October 2

Some daily events in the changing sky for September 24 – October 2.
by Alan M. MacRobert
In twilight on Friday the 24th, look for the Moon and Jupiter far apart in the east.
Sky & Telescope diagram
Friday, Sept. 24
 
As twilight descends this evening, the Moon and Jupiter come into view far apart low in the east, as shown here. The Moon is two days past full.
 
Saturday, Sept. 25
 
Jupiter's Great Red Spot should cross Jupiter's central meridian (the imaginary line down the center of the planet's disk from pole to pole) around 11:50 p.m. Eastern Daylight Time. The "red" spot appears very pale orange-tan. It should be visible for about an hour before and after in a good 4-inch telescope if the atmospheric seeing is sharp and steady. A light blue or green filter helps. For all of the Red Spot's central-meridian crossing times, good worldwide, use ourRed Spot calculator or ourlist for the rest of this observing season.
 
Now at naked-eye visibility, Mira in Cetus climbs the eastern sky in late evening — in this case, over hills in Iran. Click image for larger view.
Copyright Babak Tafreshi (www.twanight.org/tafreshi)
Sunday, Sept. 26
 
 
Mira, the prototype red long-period variable star in Cetus, is now visible to the unaided eye. It was magnitude 4.6 as of September 21st, on its way to a predicted maximum of about 3.7 in early October. Cetus is in good view in the east-southeast by about 11 p.m. daylight saving time. Estimate its brightness using the comparison-star chart in the SeptemberSky & Telescope, page 58.
 
Monday, Sept. 27
 
After the waning gibbous Moon rises in late evening, look for the Pleiades just to its left, by about 2° (depending on where you live).
 
 
Jupiter's Red Spot should transit around 1:28 a.m. Tuesday morning EDT; 10:28 p.m. Monday evening PDT.
 
Tuesday, Sept. 28
 
This is the time of year when, after nightfall, the dim Little Dipper (you'll need a dark sky!) dumps water into the bowl of the Big Dipper far below it in the north-northwest.
 
 
Now that the Moon is gone from the evening sky, start keeping an eye on Comet Hartley 2. It's about 7th magnitude and excellently placed in western Cassiopeia. Hartley 2 should brighten to 5th magnitude in the next three weeks. See the article and finder chart in the OctoberSky & Telescope, page 56, oronline.
 
 
Jupiter's Red Spot should transit around 9:19 p.m. EDT.
 
Wednesday, Sept. 29
 
As evening grows late and Jupiter rises high in the southeast, look for Fomalhaut, the Autumn Star, sparkling far to its lower right in the south-southeast.
 
Thursday, Sept. 30
 
Last-quarter Moon (exact at 11:52 p.m. EDT).
 
 
Jupiter's Red Spot should transit around 10:57 p.m. EDT.
 
 
The bright eclipsing variable star Algol should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 1:39 a.m. Friday morning EDT; 10:39 p.m. Thursday evening PDT. Algol takes several additional hours to fade and to rebrighten. Use ourcomparison-star chart. (For all times of Algol's minima this month, good worldwide, see the OctoberSky & Telescope, page 59, or use ourAlgol predictor.)
 
Friday, Oct. 1
 
Shortly after dark at this time of year, five constellations form a line descending from the zenith down to the west-northwest horizon. Near the zenith is the star Deneb: the head of the Northern Cross and the tail of Cygnus, the Swan. Next down is Lyra with bright Vega, then dim Hercules, then little Corona Borealis, and then big Bootes with bright Arcturus low in the west-northwest.
 
Saturday, Oct. 2
 
Jupiter's Red Spot should transit around 12:35 a.m. Sunday morning EDT; 9:35 p.m. Saturday evening PDT.