This Week’s Sky: October 13 – 20

Jupiter and the last-quarter Moon steal the predawn show.

All Week

SW-45min after sunset

The evening sky, facing southwest 45 minutes after sunset.

With Saturn fighting a losing battle against twilight, Mars is essentially the only naked-eye evening planet. It’s been moving eastward at a pace great enough to keep it from losing too much ground to twilight. This week the red planet resides in the non-zodiacal constellation of Ophiuchus (to the confoundment of astrologers everywhere) as it heads toward Sagittarius. Mars sets at around 9:30 p.m., local daylight time. At 2 a.m., big, bright Jupiter clears the eastern horizon. The planet is an increasingly rewarding predawn sight in a good telescope.

October 14

Mars + Theta Oph

The view of Mars and Theta (θ) Ophiuchi in a small telescope at low power.

Tonight Mars will lie a mere 20 arcminutes (less than one Moon diameter) from the 3.2-magnitude star, Theta (θ) Ophiuchi. The 0.9-magnitude planet greatly outshines the star, but the pairing should make for an interesting telescopic sight. See how long it takes for you to notice Mars’s shifting position — it moves noticeably in only one hour.

October 15

Seronik-LQ Moon

The last-quarter Moon. Courtesy Gary Seronik

The Moon is at last-quarter this morning. (It actually hits that mark at 3:12 p.m., EDT.) This is an excellent time of year for this phase — the Moon rises early and rides high on the ecliptic in Gemini.

October 17

Moon and Jupiter

The Moon nears Jupiter in the predawn. (For clarity, the Moon is shown larger than it actually appears in the sky.)

In the predawn, the Moon and Jupiter have a moderately close encounter. The two are separated by a little more than seven degrees and will make for a striking naked-eye sight. Tomorrow they will still be close, but a degree farther apart.

October 20

Another window of opportunity for observing the zodiacal light opens this morning. Look for a faint, cone-shaped glow emanating from the eastern horizon.

Weekend Stargazer


Open Cluster NGC7789. Courtesy Ron Brecher

With the Moon absent from the evening sky, the October 17 – 19 weekend is a good one for some autumn deep-sky observing. But rather than simply chase down the obvious Messier objects (as fine as so many of them are), stretch out a bit and try for some less famous targets. One of my favourites of the season is open cluster NGC7789, located in Cassiopeia.

NGC7789 finderchart

NGC7789 is located in western Cassiopeia. (Click on image for a larger version.) Courtesy Gary Seronik

I first stumbled across this grouping many years ago while sweeping the region with 10×70 binoculars. It was so conspicuous that I felt sure it must be a Messier object that I was simply unfamiliar with. Not so. The cluster was actually discovered by Caroline Herschel (sister of the famed British astronomer, William Herschel) in the autumn of 1783. Under dark skies, NGC7789 can be pulled in with 10×50 binos, but the best view is with a small telescope at low power. Too much magnification, or too big a scope, and the cluster begins to blend in with the background stars. Give it a try and see what you think.

For more on observing NGC7789, have a look at Ken Hewitt-White’s Scoping the Sky column in the September/October 2014 issue of SkyNews.

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