Starwatch: the October night sky

With Jupiter now lost in the Sun’s glare, our one remaining naked-eye evening planet sets around one hour before our map times. Saturn, shining at mag 0.5 and now incorporating the ashes of Cassini, is the brightest object low in the SW at nightfall.

Seen telescopically, Saturn’s disc appears 16 arcsec wide while the rings span 36 arcsec and have their N face tipped at their maximum angle of 27° to our view. Look for Saturn below-right of the young Moon on the 24th.

The Summer Triangle fills our high S sky at nightfall but is replaced by Pegasus by the map times. The right side of the Square of Pegasus points down to Fomalhaut, twinkling just above our S horizon. The leader of Piscis Austrinus, the Southern Fish, it is sometimes called the Lonely One because of its isolation. Other nearby watery groups include Capricornus the Sea Goat, Aquarius the Water Bearer and Cetus the Whale.

Another, Pisces the Fish, is unmarked on our chart but lies between Cetus and the Square. It is close to the star Omicron Piscium that Uranus stands opposite the Sun and 2,830m km away on the 19th. At mag 5.7, it is easy to spot through binoculars – search on the Web for a “Uranus finder chart” to help in locating it. The farthest planet, Neptune, is one seventh as bright at mag 7.8 and even closer to Lambda Aquarii.

Venus, a brilliant mag –3.9 morning star, climbs to stand 21° high in the ESE at sunrise on the 1st, when it is also 3° above-right of the much fainter (mag 1.8) Mars. As both track from Leo to Virgo, Venus passes close to Mars on the 5th and 6th and lies alongside the waning earthlit Moon on the 18th. Venus is 14° high at sunrise by the 31st, when it is 16° below-left of Mars and 5° above Virgo’s leader Spica.

The Orionids shower brings a flurry of fast meteors between the 16th and 30th, with 20 per hour or more visible under ideal skies from the 21st to 23rd. Diverging from a radiant point in N Orion, near the feet of Gemini, they are seen from around 22:00 BST but are most numerous during the pre-dawn as the radiant passes high in the S. Like May’s Eta Aquarids shower, the meteoroids derive from, and lie along the orbit of, Comet Halley.

October diary