The sky, Oct. 6-13: Comet Tsuchinshan-ATLAS makes its appearance

Special to CosmicTribune.com, October 7, 2024

Excerpts from weekly Sky&Telescope report.

Crescent Moon passing Venus and Antares in twilight, Oct 4-7, 2024

The low-riding waxing crescent Moon of early fall passes Venus, then Antares in the fading afterglow of sunset.

Venus is plotted here at its position on October 5th (for North America), when it’s just 0.9° lower left of Alpha Librae, magnitude 2.8. Every day Venus moves 1.3° farther to the upper left with respect to the star.

SUNDAY, OCTOBER 6

■ After dark look just above the northeast horizon — far below high Cassiopeia — for bright Capella on the rise.

MONDAY, OCTOBER 7

■ Now the crescent Moon shines just a few degrees east (left) of Antares, as shown above.

■ The starry W of Cassiopeia stands high in the northeast after dark. The right-hand side of the W (the brightest side) is on top.

Look at the second segment of the W counting down from the top. It’s not quite horizontal. Notice the dim naked-eye stars along that segment (not counting its two ends). The brightest of these, on the right, is Eta Cassiopeiae, magnitude 3.4. It’s a remarkably Sun-like star just 19 light-years away. But unlike the Sun it has an orange-dwarf companion, magnitude 7.3, separation 13 arcseconds — making it a lovely binary in a telescope.

Left of Eta, and quite a bit fainter, is a naked-eye pair in a dark sky: Upsilon and Upsilon2 Cassiopeiae, 0.3° apart, magnitudes 4.8 and 4.6. They’re yellow-orange giants unrelated to each other, 200 and 400 light-years from us. Upsilon2 is slightly the brighter of the pair. It’s also the closer one.

TUESDAY, OCTOBER 8

■ Vega is the brightest star just west of overhead after dark. When you face west and look high, to the right of Vega by 14° (nearly a fist and a half at arm’s length), you’ll find Eltanin, the nose of Draco the Dragon. The rest of Draco’s fainter, lozenge-shaped head is a little farther to the right. Draco always eyes Vega as they wheel around the sky.

The main stars of Vega’s own constellation, Lyra — faint by comparison — extend from Vega in the opposite direction from Eltanin.

WEDNESDAY, OCTOBER 9

■ Soon after dark, you’ll find zero-magnitude Arcturus low in the west-northwest at the same height as zero-magnitude Capella in the northeast. When this happens, turn to the south-southeast, and there will be 1st-magnitude Fomalhaut at about the same height too — exactly so if you’re at latitude 43° north.

THURSDAY, OCTOBER 10

■ First-quarter Moon; it’s exactly first quarter at 2:55 p.m. EDT.

After dark, look a little to the Moon’s right or lower right for the four-star handle of the Sagittarius Teapot. Very high above the Moon (by three or four fists), that bright star there is Altair, one of our near stellar neighbors. It’s just 17 light-years away.

FRIDAY, OCTOBER 11

■ Bright comet low in twilight! Comet Tsuchinshan-ATLAS (C/2003 A3) swung through perihelion on September 27th, passing 0.39 a.u. from the Sun. Now, as its solar roasting continues, it emerges low into the Northern Hemisphere’s evening-twilight sky with its head likely to be shining at around magnitude –1 or brighter.

Start trying for the comet this evening, but it might not be easy yet. Find a place with a clear view almost right down to the horizon due west. Thirty minutes after sunset, examine the sky there just 4° or so above horizontal. That’s only two or three finger-widths at arm’s length.

Alternatively: The comet’s head will be about 28° — meaning almost three fist-widths — to the right of bright Venus, and probably somewhat lower depending on your latitude.

It will likely appear tiny and not as quite bright as Arcturus, which is sparkling some two fists to the comet’s upper right. Its bright inner tail will curve the right. The comet sets while twilight is still fairly bright.

Tomorrow it’ll be higher and better. The view will continue to improve every evening after that, and the tail will turn upward. The comet shouldn’t start losing brightness for about a week!

Mars shines in Gemini before dawn around Oct 12, 2024

If you’re up before dawn, watch Mars moving farther east (left) across Gemini from morning to morning.

SATURDAY, OCTOBER 12

■ Now Comet Tsuchinshan-ATLAS stands higher, about 8° above the west horizon 30 minutes after sunset (as seen from mid-northern latitudes). Again, bring binoculars.

Sixty minutes after sunset, as a few stars are beginning to come out, its head is still 5° above the horizon’s west point. The head sets around twilight’s end, but as darkness becomes complete the long dust tail may be detectable extending fairly far — depending on your light pollution.

SUNDAY, OCTOBER 13

■ And now the comet ‘s head is still a fine 9° high or so 60 minutes after sunset. It appears just about midway from Venus to Arcturus. By now it is predicted to grow a thin, faint antitail pointing opposite the main tail. (An antitail can appear when Earth passes through the plane of a comet’s orbit and we see a thin, broad sheet of its dust debris edge-on.) At twilight’s end, the comet is still a couple degrees over the horizon. However, when any celestial body is that low, atmospheric extinction dims it considerably. The comet is now 20° left or lower left of Arcturus.

It will get nicely higher and easier through the rest of the coming week while, in all likelihood, fading hardly at all. But the evening sky is getting poorer; the light of the waxing gibbous Moon grows brighter. The Moon is full on the evenings of the 16th and 17th.

Not until the 19th or 20th will we start getting a moonless, dark-sky observing window right after the end of twilight. By then the comet will be crossing Ophiuchus nice and high in the west-southwest.

From Sunday night to Monday night, the waxing gibbous Moon steps eastward past Saturn in the evening sky (Oct. 13 to 14, 2024).

Between Sunday evening and Monday evening for the Americas, the waxing gibbous Moon creeps eastward past Saturn in the evening sky.

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