Whale Of A Star Occulted By Tonight’s Half-Moon

This will be the view from Chicago at 10:35 p.m. Central Time (10:17 p.m. for Duluth, Minn.) tonight moments before the star is occulted. Stellarium

Like whale watching? A star called Xi22) Ceti (prounced “zye-two”) in the constellation Cetus the Whale will be occulted tonight (Jan. 24) by the half moon. While not a prominent star (only magnitude 4.3), it’s bright enough to watch disappear behind the moon’s dark limb with the smallest of telescopes and possibly even a pair of binoculars. The star blinks out around 11:30 p.m. Eastern Time, 10:30 Central, 9:30 Mountain and 8:30 Pacific.

Since I’m not aware of a table of times of the star’s disappearance for various cities, you’re on your own here. You can either check 15-20 minutes before the times shown above or do the following. Download Stellarium at stellarium.org for either Mac or Windows, install and then set your location and today’s date. Click on the Sky and Viewing options icon in the lower left of your screen (it magically appears if you hover your cursor there) and under the Sky tab, uncheck Scale Moon.

The graze line, which cuts across the mid-section of the U.S., divides the area where the occultation is visible (north) from where it’s not (south). Observers on the line can watch the star appear and disappear multiple times along the moon’s edge. Google / Brad Timerson

Now, set the time close to the one that fits your time zone (above) and advance the clock forward or backward minute by minute until the star appears near the moon’s left (east) edge. Point your scope at the moon about 10 minutes beforehand, then watch it devour the star in an instant when the time comes. Because the moon’s only half, you’ll probably be able to make out its dark edge in your telescope, which will make it easier to anticipate exactly when Xi2 will vanish. I know this sounds like a bunch of hoops.

The moon strays from the familiar zodiac constellations into Cetus the Whale tonight where it occults Xi-2 in the head of the beast. Stellarium

Xi2 is about 190 light years from Earth and shines pure white. Only the northern half of the country will see it occulted; for the southern half, the star slips just south of the moon. Along a line stretching from New Jersey through central Illinois across Colorado to just south of San Francisco, skywatchers will see the star graze the moon’s edge. This is always a special treat — instead of a simple disappearance, it will pop in and out of view multiple times as it “scrapes” the moon’s edge. Lunar mountains blank the star from view, valleys let it shine through. Since the moon continually moves eastward as it orbits Earth, the star will appear to flash in and out of view.

Take advantage of this event especially if you live on or near the graze line. Oh, and don’t forget to look at the moon itself. It’s crazy with craters in its current phase! Even in 10x binoculars.