Sky at a Glance September 9 – 16

Photo showing the constellation Capricornus, rising due south about 10 pm this week.

This Week’s Sky at a Glance, September 9 – 16 ~by Curt Nason

The constellation Capricornus is a large chevron shape that is due south around 10 pm this week. A pair of stars marks each upper corner, and both stars of the western pair are colourful wide double stars in binoculars. The sea goat arises from a tale of the Olympian gods being surprised by Typhon, the most ferocious of the rival Titans. Knowing Typhon was not fond of water, the gods changed into fish and escaped to the sea. The god Pan, who was half-goat and half-man, panicked and dove in before the transformation was complete and wound up with a goat’s head and the tail of a fish.

There are four common targets for backyard telescope users near Capricornus, but only the globular cluster M30 off the east side of the chevron is officially within its borders. It is also the easiest of the targets for binoculars. The globular cluster M75 lies west of the chevron in Sagittarius, while globular cluster M72 and the four-star (literally four stars, it is not an observing highlight) asterism M73 are above in Aquarius. Nearby is the more challenging, but worth the effort, Saturn Nebula, the gaseous remnant of a dead star that somewhat resembles the ringed planet.

A few millennia ago the Sun was in Capricornus at the winter solstice, when at midday it is overhead at its most southerly point at latitude -23.5 degrees. This is the southern border of the tropics, and it is still called the Tropic of Capricorn despite the Sun being in Sagittarius at this time. Earth’s 25,800 year polar wobble, called the precession of the equinox, is responsible for this shift.

This Week in the Solar System

Saturday’s sunrise in Moncton is at 6:50 am and sunset will occur at 7:41 pm, giving 12 hours, 51 minutes of daylight (6:55 am and 7:46 pm in Saint John). Next Saturday the Sun will rise at 6:58 am and set at 7:28 pm, giving 12 hours, 30 minutes of daylight (7:04 am and 7:32 pm in Saint John).

The Moon is at third quarter on Wednesday, rising a little before midnight Tuesday and setting at 3 pm. Around 10 am Tuesday, telescope users at high magnification might be able to see the Moon occult Aldebaran in daylight. Jupiter was in astronomical conjunction with Spica on September 5, having the same right ascension as Virgo’s brightest star. From our viewpoint, they will appear to be in conjunction on September 16 as Jupiter sits a few degrees above Spica, having the same azimuth. Saturn remains in good viewing position in the south after sunset, with its rings proudly on display for telescope users. Venus dominates the eastern morning sky despite being near its dimmest. Mercury is at greatest elongation on Tuesday, and it can be seen with binoculars near Regulus on Sunday and near Mars next Saturday.

The Saint John Astronomy Club and RASC NB share a meeting at the Rockwood Park Interpretation Centre on Saturday, September 9 at 1 pm. The William Brydone Jack Astronomy Club meets at the UNB Forestry / Earth Sciences Building in Fredericton at 7 pm on Tuesday. All are welcome. The RASC NB star party at Fundy National Park takes place September 15 and 16 at the South Chignecto campground.

Questions? Contact Curt Nason.

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