October 2021

Welcome to SkyEye, your guide to this month's celestial events.

The Calendar

The Draconid meteor shower early in the month is enhanced by moonless skies but the Full Moon on the twentieth obliterates the Orionids. Venus attains greatest elongation east late in October but Mars is lost to view as it undergoes conjunction.

The phases of the Moon in October 2021

Date Body Event
2 Venus aphelion
6 Moon new
8 Earth Draconid meteor shower
Mars conjunction
Moon perigee
9 Moon descending node
Mercury inferior conjunction
Mercury, Mars conjunction: 2.4° apart
11 Saturn stationary point in right ascension: retrograde → direct
13 Moon first quarter
15 Mercury ascending node
16 Venus 1.4° north of Antares
17 136199 Eris opposition
18 Mercury stationary point in right ascension: retrograde → direct
Jupiter stationary point in right ascension: retrograde → direct
20 Mercury perihelion
Moon full: Hunter's Moon
21 Earth Orionid meteor shower
136108 Haumea opposition
Moon, Uranus 1.3° apart
23 Moon ascending node
24 Moon apogee
25 Mercury greatest elongation west: 18.4°
28 Moon last quarter
29 Venus greatest elongation east: 47.0°
30 Saturn east quadrature

The Solar System

The word planet is derived from the Greek word for 'wanderer'. Unlike the background stars, planets seem to move around the sky, keeping mostly to a narrow track called the ecliptic, the path of the Sun across the stars. Dwarf planets and small solar-system bodies, including comets, are not so constrained, often moving far above or below the ecliptic.

The position of the Sun and planets at mid-month

Sun VirgoLibra

Mercury Virgo

Already gone from the evening skies as viewed from northern temperate latitudes, southern hemisphere observers watch Mercury plummet toward the horizon during the first week of October with the planet undergoing inferior conjunction on 9 October. It is 2.5° south of Mars on the same day but neither object will be visible due to their proximities to the Sun. Mercury returns to the dawn skies in what is the best morning apparition of 2021 for northern observers (and the worst for the south). The tiny planet resumes direct motion on 18 October and reaches its fourth and final perihelion of the year on 20 October. Greatest elongation west of 18.4° occurs five days later. Mercury brightens steadily from conjunction, ending the month in negative magnitudes.

Venus LibraScorpiusOphiuchusScorpiusOphiuchus

Venus reaches aphelion on the second day of the month. One week later, the waxing crescent Moon passes just under 3° north of the evening star. Venus has had close encounters with two first-magnitude stars so far this year; it has a third one this month when, on 16 October, the bright planet is found 1.4° north of Antares. Venus remains close to the western horizon for observers in northern temperate latitudes but the evening star appears high above the sunset horizon for those viewing it from the southern hemisphere. Greatest elongation east of 47.0° occurs on 29 October.

Earth and Moon

The Draconid meteor shower in early October benefits from the lack of light from the New Moon. However, the Orionids are rendered unobservable by the Hunter's Moon on 20 October.

Mars Virgo

The Sun has finally caught up with Mars and the red planet undergoes conjunction on 8 October. Its rather distant appulse with Mercury the following day is unobservable. Mars returns to view as a morning sky object at the end of the month, rising just ahead of the Sun.

Jupiter Capricornus

Jupiter reaches a stationary point on 18 October and changes direction from retrograde motion to direct motion across the background stars. Look for it in the evening because it sets around midnight by the end of the month.

Saturn Capricornus

Saturn returns to direct motion on 11 October. The rings, which have been opening up slightly since May, reach a maximum value of 19.4° on the same day. The tilt will decrease for the rest of the year. East quadrature occurs on the penultimate day of the month. This configuration means that SaturnEarthSun form a right angle. The ringed planet is visible in the evening but sets at or just before midnight for all locations.

Uranus Aries

Uranus and the nearly Full Moon are only 1.3° apart on 21 October but the brilliant light from our satellite will obliterate any sight of the sixth-magnitude planet. Uranus rises in the early evening hours, anticipating next month's opposition.

Neptune Aquarius

A small telescope is necessary to view the most distant planet in the solar system. Neptune is past opposition and is already above the horizon when darkness falls. It is best observed from northern latitudes where it doesn't set until well after midnight.

The Celestial Sphere

Constellations are patterns of stars in the sky. The International Astronomical Union recognises 88 different constellations. The brightest stars as seen from the Earth are easy to spot but do you know their proper names? With a set of binoculars you can look for fainter objects such as nebulae and galaxies and star clusters or some of the closest stars to the Sun.

Descriptions of the sky for observers in both the northern and southern hemispheres are available for the following times this month. Subtract one hour from your local time if summer (daylight savings) time is in effect.

Local Time Mid-month Northern Hemisphere Equator Southern Hemisphere
1730 hours (1830 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
1930 hours (2030 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
2130 hours (2230 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
2330 hours (0030 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
0130 hours (0230 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
0330 hours (0430 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S
0530 hours (0630 hours summer time) 60° N 50° N 40° N 30° N 20° N 10° N 10° S 20° S 30° S 40° S