The gas and ice giants put on a display this month, while Pegasus is perfectly placed for exploring
When to use this chart
1 Oct at 00:00 AEST (14:00 UT)
15 Oct at 23:00 AEDT (12:00 UT)
October Highlights
Recommended equipment: Naked eye
The Moon has conjunctions with three planets in the western evening sky this month. On 9 October at the end of twilight, the three-day old crescent Moon is 7° below Venus. The following night these same objects form a triangle with the bright star Antares (Alpha (α) Scorpii). On 12 October, the Moon sits on Sagittarius’s Teapot asterism. Two days later, the now gibbous Moon is 4° to the upper right of Saturn. The next day, it’s a similar distance and position from Jupiter. The chart accurately matches the sky on the dates and times shown for Sydney, Australia. The sky is different at other times as the stars crossing it set four minutes earlier each night.
Stars and constellations
Recommended equipment: Naked eye
The northern sky is home to four mag. +2.0 stars that form the Great Square of Pegasus. Today, the constellation boundaries have the northeastern star in Andromeda, marking the head of the chained princess. Now known as Alpha (α) Andromedae, the star’s origin is revealed by its Arabic name, Alpheratz – ‘the horse’s shoulder’. It also explains why Pegasus no longer has a ‘delta’ star, with Alpha (α), Beta (β) and Gamma (γ) Pegasi, forming the ‘square’.
The Planets
Recommended equipment: Naked eye
Venus is well placed in the western early evening sky, reaching its highest point at the end of the month. As dusk ends, Saturn and Jupiter are high in the north. In late October Saturn reaches its eastern quadrature, when you’ll see the planet’s shadow cast on its rings. October is also great for seeing the ice giants – Neptune transits the meridian (due north) mid-evening, shortly before Uranus.
Deep-sky objects
Recommended equipment: Large telescope
The southwestern (top left) star of the Great Square of Pegasus is Markab (Alpha (α) Pegasi), the gateway to the mag. +10.9 galaxy NGC 7479 (RA 23h 04.9m, dec. +12° 19’). Located 3° south of the star, this face-on spiral has a distinctive bar with a bright nucleus. Its halo extends from the bar’s ends. With sufficient aperture (25cm), averted vision reveals two arms. The southern end is the most prominent, curving westwards.
Recommended equipment: Small/medium telescope
Continue southwards through Pegasus another 3.5° and you’ll find an obvious trapezium made up of four mag. +5.0 stars that fit within a 1.5° circle – ideal for observing with binoculars. Two stars are blue-white in colour, while the others are orange. One member is the double star 57 Pegasi (RA 23h 09.5m, dec. +8° 41’). This pair is mag. +5.0 and mag. +9.6, coloured yellowish orange and blue respectively, about 32.5 arcseconds apart.