This Week's Sky at a Glance, October 4 – 13

The bright Comet Tsuchinshan-ATLAS has swung around the Sun and will finally emerge low in evening twilight late this week for us in the world's mid-northern latitudes. Binoculars will help you pick it up through the twilight, quite low due west, starting around October 10th or 11th. Its tiny head will probably shine at about magnitude 0 or maybe brighter. Its long tail, once the sky grows dark enough, will point more or less to the right this evening. In just the next couple days the tail will swing upward. See October 11th below — and especially Bob King's thorough article Get Ready for Comet Tsuchinshan-ATLAS — The Best Is Yet to Come!

FRIDAY, OCTOBER 4

■ The Great Square of Pegasus balances on one corner high in the east through much of the evening. Two fists at arm's length to the Square's lower right shines Saturn, somewhat brighter.

Extending away from the Great Square's left corner is the main line of Andromeda: three 2nd-magnitude stars about as bright as those of the Square and spaced similarly far apart. (The three include the Square's corner itself.) This whole dipper-shaped pattern was named the Andromegasus Dipper by the late Sky & Telescope columnist George Lovi — joining the legendary Big and Little Dippers, the Milk Dipper of Sagittarius (nowadays usually subsumed into the Teapot), and the tiny dipper pattern of the Pleiades.

SATURDAY, OCTOBER 5

■ About a half hour after sunset, find the thin waxing crescent Moon paired with Venus very low in the southwest as shown above. They're about 4° apart. A much harder catch is faint Alpha Librae, just under 1° to Venus's upper right this evening.

SUNDAY, OCTOBER 6

■ After dark look just above the northeast horizon — far below high Cassiopeia — for bright Capella on the rise. How soon Capella rises, and how high you'll find it, depend on your latitude. The farther north you are, the sooner and higher.

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: Upsilon¹ 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.

In the other direction, Draco's long, arched back and tail loop around the Little Dipper.

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 (Boston, Buffalo, Milwaukee, Boise, Eugene). Seen from south of that latitude Fomalhaut will appear higher; from north of there it will be lower.

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 0 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 5° or so above horizontal. That's about 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 maybe not as quite bright as Arcturus, which is sparkling at magnitude 0 some two fists to the comet's upper right. The bright inner tail will curve the right. The comet sets while twilight is still fairly bright.

Tomorrow it'll be about 4° higher and a little easier. The view will continue to improve every evening after that, and the tail will swing around upward. The comet shouldn't start losing brightness for about a week.

See Bob King's excellent Get Ready for Comet Tsuchinshan-ATLAS — The Best Is Yet to Come! It has a finder chart through the end of October.

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 only a little. 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, but (probably) visibly receding.

This Week's Planet Roundup

Mercury is out of sight very deep in the sunset.

Venus, magnitude –3.9, gleams low in the west-southwest as evening twilight fades. It sets around twilight's end.

You can use Venus as a twilight guidepost for locating Comet Tsuchinshan-ATLAS starting late this week. It's almost three fists to Venus's lower right, right, or upper right depending on the date and your latitude. See the chart in Get Ready for Comet Tsuchinshan-ATLAS — The Best Is Yet to Come! (The chart is drawn for latitude 40° north.)

Mars and Jupiter, magnitudes +0.4 and –2.5, respectively, rise in late evening and show best high in the pre-dawn sky. Watch for Jupiter to rise in the east-northeast around 9 or 10 p.m. daylight-saving time. (The orangy point about a fist at arm's length to its right or upper right is Aldebaran.) Mars comes up two hours later, nearly three fists to Jupiter's lower left.

Once they're well up, you'll see that Jupiter is shining in Taurus near the Bull's horntip stars, Beta and Zeta Tauri. Mars is crawling through Gemini, now crossing the stick figure of the Pollux twin (who is lying on his side).

Both planets are highest toward the south before the beginning of dawn, where they shine through thinner, steadier air for the best telescopic views. Jupiter is now a nice 43 arcseconds wide; it will enlarge month by month toward its opposition in December. Mars in a telescope is still a visually disappointing little yellow-orange blob, 8 arcseconds wide, on its way to a fairly mediocre opposition next January.

Saturn, magnitude +0.7 in Aquarius, is nicely up in the southeast as the stars come out. It's two fists lower right of the Great Square of Pegasus, which balances on one corner after dark. The Square's upper-right edge points to Saturn. By 10 p.m. daylight-saving time, Saturn is about as high toward the south as it will get.

Uranus (magnitude 5.6, in western Taurus) is 25° west of Jupiter, so it's well up by late evening. You'll need a good finder chart to identify it among surrounding faint stars.

Neptune (tougher at magnitude 7.8, near the Circlet of Pisces) is 14° east of Saturn. Again you'll need a proper finder chart.

All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions and graphics that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time minus 4 hours. UT is also known as UTC, GMT, or Z time.

Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For a more detailed constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy.

Once you get a telescope, to put it to good use you'll need a much more detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows all stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. It's currently out of print. The next up, once you know your way around well, are the even larger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to mag 9.75). And read How to Use a Star Chart with a Telescope. It applies just as much to charts on your phone or tablet as to charts on paper.

You'll also want a good deep-sky guidebook. A beloved old classic is the three-volume Burnham's Celestial Handbook. An impressive more modern one is the big Night Sky Observer's Guide set (2+ volumes) by Kepple and Sanner. The pinnacle for total astro-geeks is the Annals of the Deep Sky series, currently at 10 volumes as it slowly works forward through the constellations alphabetically. So far it's only up to F.

Can computerized telescopes replace charts? Not for beginners I don't think, and not for scopes on mounts and tripods that are less than top-quality mechanically. Unless, that is, you prefer spending your time getting finicky technology to work rather than learning how to explore the sky. As Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand and a curious mind." Without these, "the sky never becomes a friendly place."

If you do get a computerized scope, make sure that its drives can be disengaged so you can swing it around and point it readily by hand when you want to, rather than only slowly by the electric motors (which eat batteries).

However, finding faint telescopic objects the old-fashioned way with charts isn't simple either. Learn the essential tricks at How to Use a Star Chart with a Telescope.

Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty's monthly
podcast tour of the naked-eye heavens above. It's free.

"The dangers of not thinking clearly are much greater now than ever before. It's not that there's something new in our way of thinking, it's that credulous and confused thinking can be much more lethal in ways it was never before."
            — Carl Sagan, 1996

"Facts are stubborn things."
            — John Adams, 1770