Special to CosmicTribune.com, November 25, 2024

Excerpts from weekly Sky&Telescope report.

MONDAY, NOVEMBER 25

■ The Andromeda Galaxy (M31) and the Perseus Double Cluster are two of the most famous deep-sky objects. They’re both cataloged as 4th magnitude, and in a fairly good sky you can see each with the unaided eye. Binoculars make them easier. Did you know they’re only 22° apart? They’re very high toward the east early these evenings — to the right of Cassiopeia and closer below Cassiopeia, respectively.

But they look rather different, the more so the darker your sky. See for yourself.

■ Algol should be at its minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 8:14 p.m. EST. It takes several additional hours to rebrighten.

TUESDAY, NOVEMBER 26

■ The thin waning crescent Moon occults Spica before or during dawn Wednesday morning the 27th for most of the eastern and central U.S. and Canada. Spica will disappear behind the Moon’s bright limb, then will emerge from behind its dark limb up to an hour or more later.

What’s wrong with this picture? Nothing, if you know that the Moon in these scenes is always drawn three times its actual size. . . and that the Moon is always positioned for an observer at 40° north latitude, 90° east longitude: that’s near Peoria, Illinois, and is roughly the center of North America’s population. So your Moon position with respect to Spica in early dawn will probably differ a bit, and that matters a lot for occultations.

The southern limit of the occultation, or graze line, runs from southeasternmost Texas into New Mexico, passing north of Austin and through northern Houston. The Moon and Spica there will be low. Complex occultation events are possible very close to the graze line, and the International Occultation Timing Association (IOTA) plans an expedition using predictions refined to the city-block level. Spica is a very close double star. Video of a previous Spica graze.

WEDNESDAY, NOVEMBER 27

■ The Double Cluster is Perseus’s most famous deep-sky object but by no means its biggest or brightest! That would be the big Alpha Persei Association. Binoculars are the perfect instrument for this swarm of stars born in the same area around the same time. It’s called an “association” rather than a “cluster” because it’s not gravitationally bound; its stars will simply drift apart.

The Alpha Per Association appears about 3° long, the size of your thumbprint at arm’s length, or roughly half the width of an ordinary binocular’s field of view. Find it running south-southeast (currently down or lower right) from Perseus’s brightest star. Matt Wedel notes that its sheer size makes it so overlooked!

THURSDAY, NOVEMBER 28

■ Does the Sun already seem to be setting about as early as it ever will? You’re right! We’re still nearly a month from the winter solstice — but the Sun sets its earliest around December 7th if you’re near latitude 40° north. And already the Sun sets within only about 2 minutes of that time.

A surprising result of this: The Sun actually sets a trace earlier on Thanksgiving than on Christmas — even though Christmas is around solstice time!

But in celestial mechanics, every abnormality is balanced out by an equal abnormality somewhere else. The offset of the earliest sunset from the solstice date is balanced out by the opposite happening at sunrise: The Sun doesn’t come up its latest until January 4th. Blame the tilt of Earth’s axis and the eccentricity of Earth’s orbit.

FRIDAY, NOVEMBER 29

■ As the stars come out, the Cassiopeia W now stands on end (its fainter end) high in the northeast. Watch Cas turn around to become a flattened M, even higher in the north, by late evening.

SATURDAY, NOVEMBER 30

■ Vega still shines brightly well up in the west-northwest after dark. The brightest star above it is Deneb, the head of the big Northern Cross, formed by the brightest stars of Cygnus. At nightfall the shaft of the cross extends lower left from Deneb. By about 11 p.m., it plants itself more or less upright on the northwest horizon.

SUNDAY, DECEMBER 1

■ Telescope users can watch the tiny black shadow of Jupiter’s moon Io start crossing Jupiter’s face at 9:02 p.m. EST (entering on the planet’s eastern edge), closely followed by Io itself just 10 minutes later. They depart Jupiter’s opposite edge at 11:14 and 11:23 p.m. EST, respectively. Convert to your own time zone. Meanwhile, Jupiter’s Great Red Spot will be out of sight on the planet’s far side.

■ New Moon (exact at 1:21 a.m. on this date EST).

  Nov. 25-Dec. 1, starring the Andromeda Galaxy and Perseus Double Cluster, The Sky