This Week’s Sky at a Glance, October 23 – 31

Venus, Jupiter, Mars at dawn Oct. 24-25-26, 2015

Big doings at dawn! High in the east, the two brightest celestial objects after the Sun and Moon go through a close conjunction, while Mars looks on just below. Mercury lurks near the horizon.

Friday, October 23

• The Venus-Jupiter-Mars assemblage at dawn finally reaches its peak on Saturday through Monday mornings, as shown above. The best views should be about an hour before your local sunrise time. Mercury, very far below them, shows best a little later in the dawn as it edges higher. See our story Venus-Jupiter Conjunction This Weekend, and pass it on to your family and friends!

Saturday, October 24

• Look upper left of the waxing gibbous Moon this evening for the Great Square of Pegasus balancing on one corner.

Venus and Jupiter are in conjunction in the dawns of Sunday and Monday, 1.1° apart as seen from the time zones of the Americas.

Sunday, October 25

• The Venus-Jupiter conjunction continues at dawn Monday morning. And Venus happens to be at its greatest elongation, 46° west of the Sun.

Monday, October 26

• The brightest asteroid, 4 Vesta, is visible in binoculars at magnitude 6.8 this week. It's in the tail (western) end of Cetus, well up in the southeast to south after dinnertime. Use the finder chart in the October Sky & Telescope, page 48.

Tuesday, October 27

• Full Moon (exact at 8:05 a.m. Eastern Daylight Time). The Moon rises shortly after sunset for North America. After dark look above it, by about a fist and a half at arm's length, for the two or three brightest stars of Aries lined up horizontally. The brightest, Alpha Arietis or Hamal (on the left), is an orange giant.

Wednesday, October 28

• This is the time of year when the Big Dipper lies horizontal low in the north-northwest early in the evening. How low? The farther south you are, the lower. Seen from 40° north (New York, Denver) its bottom stars twinkle nearly ten degrees high, and the larger, dimmer Great Bear pattern walks upright on the horizon toward the right. But at Miami (26° N) the entire Dipper and Bear skim along below the northern horizon out of sight.

Thursday, October 29

The Ghost of Summer Suns. Halloween is approaching, and this means that Arcturus, the star sparkling low in the west-northwest in twilight, is taking on its role as "the Ghost of Summer Suns." What does this mean? For several days centered on October 29th every year, Arcturus occupies a special place above your local landscape. It closely marks the spot there where the Sun stood at the same time, by the clock, during warm June and July — in broad daylight, of course.

So, in the last days of October each year, you can think of Arcturus as the chilly Halloween ghost of the departed summer Sun.

• The Moon occults Aldebaran for Europe and much of Asia (map, timetables), but if that's not where you are, you can watch Gianluca Masi's live webcast of the event from the Virtual Telescope Project. The webcast starts at 5:00 p.m. EDT (21:00 UT).

Venus, Jupiter, Mars before dawn Oct. 31, 2015

By the morning of the 31st, Venus has pulled away from Jupiter and is nearing its conjunction with Mars.

Friday, October 30

• Sometime around 7 or 8 p.m., depending on where you live in your time zone, bright Capella is exactly as high in the northeast as Fomalhaut is in the south.

• On Saturday (North American date), the quarter-mile asteroid 2015 TB145 passes 1.3 lunar distances from Earth. It will reach 10th or 11th magnitude (100 times too faint to see with the unaided eye) as it crosses the northern sky of the early-morning hours. See our article and chart: Close-in Asteroid Offers Halloween Treat.

Webcast of the flyby: Gianluca Masi has marshaled a network of observers to provide real-time views via his Virtual Telescope Project. Watch the webcast starting at 0:00 UT October 31st, which is 8:00 p.m. October 30th EDT.

Saturday, October 31

• The waning gibbous Moon this Halloween doesn't rise till around 9 p.m. (depending on where you are). Once the Moon is well up, look for Orion far to its right, and Gemini's Castor and Pollux off to its left.

• Daylight-saving time ends at 2 a.m. Sunday morning. Clocks fall back an hour (for most of North America).

• In Sunday's dawn, Venus has drawn to within 1.1° of little Mars, even closer than shown here. Mars is only 1/250 as bright. They'll appear closest together, 0.7° or 0.8° apart, on the mornings of Monday and Tuesday November 2nd and 3rd.


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 an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

Pocket Sky Atlas

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's still less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and once you know your way around, the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). 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."

This Week's Planet Roundup

Mercury is bright (magnitude –0.9) but low in the east at dawn, getting lower every day. Look for it about 45 minutes before sunrise, far beneath and perhaps a bit left of Venus, Jupiter, and Mars as shown at the top of this page.

Venus, Mars, and Jupiter show off together in the east before and during dawn. Venus is the brightest at magnitude –4.5. Jupiter is –1.8, and Mars, much closer to Jupiter, is much fainter at +1.7.

Venus and Jupiter are in conjunction, 1.1° apart, on Sunday and Monday mornings October 25th and 26th. That's about a fingertip-width at arm's length. Mars is below them. . . for now. The three form a "trio" (fitting within a circle 5° in diameter) from October 22nd through 29th. Read the whole story, and pass it on to family and friends.

Saturn (magnitude +0.6) disappears very low in the southwest during twilight. Bring binoculars. Don't confuse it with orange Antares twinkling 9° to its left.

Uranus (magnitude +5.7, in Pisces) and Neptune (magnitude +7.8, in Aquarius) are high in the southeast and south, respectively, by 9 p.m. Finder charts for Uranus and Neptune.


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 that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.


“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”

— Neil deGrasse Tyson


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