This Week’s Sky at a Glance, Sept. 25 – Oct. 3

Regulus passing slightly-fainter Mars in early dawn, Sept. 25, 2015

In early dawn, Mars passed Regulus on the morning of the 25th. They're still 1.1° apart on Saturday morning the 26th. After that they widen by about ½° per day.

Venus, Regulus, Mars and Jupiter at dawn in early October 2015

By Saturday morning October 3rd, Mars moves nearly halfway from Regulus to Jupiter. The blue 10° scale is about the width of your fist at arm's length.

Friday, September 25

• Look far below the Moon this evening for 1st-magnitude Fomalhaut coming into view. Fomalhaut rises in late twilight. How soon can you spot it?

• Algol should be at minimum brightness for a couple hours centered on 6:09 p.m. EDT (according to Algol's recently updated schedule). It takes several additional hours to rebrighten.

Saturday, September 26

• With fall under way, Deneb is taking over from Vega as the zenith star at nightfall (for skywatchers at mid-northern latitudes). Look straight up after the end of twilight.

Sunday, September 27

Total eclipse of the Moon! The eclipse happens for North America in the evening, South America later at night local time, and for Europe and much of Africa on the morning of Monday the 28th local time. Timetables and map. For more on the eclipse, including how to do crater timings, see the September Sky & Telescope, page 26.

It it cloudy? Are you on the other side of the world? We'll webcast the lunar eclipse, with commentary by S&T editors and lunar scientists. We start at 9 p.m. Sunday evening EDT (1:00 Sept. 28 UT/GMT).

On a night when the Moon gets eclipsed, it's always full.

Monday, September 28

• The Moon, a day past full, rises in the east in twilight. When the stars come out, look high above it for the Great Square of Pegasus.

Tuesday, September 29

• Vesta, the brightest asteroid, is at opposition. All week it remains magnitude 6.2, easy in binoculars (despite the moonlight) as it creeps through western Cetus. Use the finder charts in the September Sky & Telescope, pages 48–49.

Uranus, magnitude 5.7, is also nearby! Finder chart.

Wednesday, September 30

• As the stars come out, Cassiopeia is already higher in the northeast now than the sinking Big Dipper is in the northwest. The right side of Cassiopeia's broad W pattern tilts upward.

Thursday, October 1

• The waning gibbous Moon rises around 9 or 10 p.m., shining in the Hyades near Aldebaran. The Moon occults Aldebaran during dawn Friday morning for the West Coast, and in broad daylight Friday morning for telescope users in nearly all the rest of the U.S. and Canada. See the map and times in the October Sky & Telescope, page 49.

Friday, October 2

• After dark, look just above the northeast horizon — far below 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.

Saturday, October 3

• By midnight or so, the waning Moon rises in the east-northeast. And to its right in the east, Orion is rising. The first bright star you hit looking right of the Moon is Betelgeuse: Orion's orange shoulder.

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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 out of sight; it passes through inferior conjunction with the Sun on September 30th.

Venus (magnitude –4.7) blazes as the "Morning Star" high in the east during dawn. It rises much earlier than that, around 3 or 4 a.m. depending on your location; a weird UFO of a thing. In a telescope Venus is a thickening crescent, but shrinking in diameter week by week as it pulls farther ahead of Earth around the Sun.

Mars, 400 times fainter at magnitude +1.8, glows lower left of Venus near Regulus, which is a bit brighter at magnitude +1.4. Mars and Regulus are slightly more than 1° apart on Saturday morning September 26th. They widen to just over 5° apart by Saturday October 3rd, as shown above.

Jupiter (magnitude –1.7) is below or lower left of Mars, Regulus, and Venus in early dawn, as shown above. All three planets are in the constellation Leo.

Saturn (magnitude +0.6, at the Scorpius-Libra border) is sinking ever lower in the southwest at dusk. Left of it by 11° twinkles orange Antares.

Uranus (magnitude +5.7, in Pisces) and Neptune (magnitude +7.8, in Aquarius) are well up in the east and southeast, respectively, by 9 or 10 p.m. Finder charts for Uranus and Neptune.

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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.

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“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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