SkyEye

The Calendar

The Moon has a busy month! The first Full Moon in October is the Harvest Moon, the Full Moon nearest to the (northern hemisphere) autumnal equinox. The second Full Moon is this year's 'Micro Moon', not to mention a calendrical 'Blue Moon'. Mars and Uranus both reach opposition in October and Venus performs a flyby of Regulus in the morning skies.

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.

Sun Virgo → Libra

Mercury Virgo → Libra → Virgo

The month opens with Mercury at greatest elongation east (25.8°) of the Sun. This is the beginning of the end of the best evening apparition of the year for southern hemisphere observers. Mercury goes into retrograde on 14 October, dims dramatically and vanishes from view before the end of the month as it reaches inferior conjunction on 25 October. However, the last morning apparition of 2020 gets underway immediately afterwards when northern observers will get their best dawn views of this elusive object.

Venus Leo → Virgo

The morning star is just 0.1° away from Regulus, the brightest star in the constellation of Leo, on the second day of the month. Brilliant Venus, glowing at magnitude −4.1, far outshines first-magnitude Regulus, the faintest of the first-magnitude stars in our sky. Venus is appearing a little lower above the eastern horizon every morning but is still well-placed for viewing in the dawn sky, particularly for northern hemisphere observers. The planet reaches perihelion on the penultimate day of the month.

Earth and Moon

The skies above Earth are particularly well lit this month with the appearance of two Full Moons, the first on the first day of the month and the second on the last day of the month. The first Full Moon is also commonly called the Harvest Moon as it is the closest Full Moon to the northern hemisphere autumnal equinox. The Full Moon which follows is often call the Hunter's Moon. The second Full Moon in a calendar month also rejoices in the designation Blue Moon. And if that isn't enough, the second Full Moon also occurs very near apogee, making it the smallest Full Moon in terms of apparent angular diameter and gaining the title of this year's Micro Moon.

The waning gibbous Moon occults Mars on 3 October. However, it does not unduly affects the first meteor shower of the October, the Draconids, which are best observed in the evening hours. The Orionids peak before First Quarter Moon and should enjoy dark skies when the shower radiant is high in the sky.

Mars Pisces

Mars, shining at magnitude −2.5, is occulted by the waning gibbous Moon on the third day of the month. This event, which begins around 02:00 UT, is visible from the southern tip of South America and parts of the Antarctic. Three days later, the red planet makes its closest approach to Earth (just over 0.4 au). This is a full week before opposition on 13 October. The waxing gibbous Moon makes another pass by Mars on 29 October but at a more respectful distance of 3.0°. Mars is visible all night, rising at sunset and setting at sunrise, but is best viewed from southern latitudes.

Jupiter Sagittarius

Jupiter reaches east quadrature on 11 October, forming a right triangle with Earth and the Sun. The waxing crescent Moon passes 2.0° south of the bright planet 11 days later. Jupiter is slowly fading this month, from magnitude −2.4 to −2.2, as it gets farther from Earth. It is visible in the evening sky but sets before midnight for astronomers in northern temperate latitudes.

Saturn Sagittarius

East quadrature occurs for Saturn on 18 October. This is a particularly interesting time to photograph this planet, its rings and satellites as the shadows cast are somewhat off to the side, leading to some intriguing effects. The First Quarter Moon is less than 3° south of the ringed planet on 23 October. Like Jupiter, Saturn is an evening sky object, best viewed from the southern hemisphere where it remains above the horizon until around midnight.

Uranus Aries

Uranus finally reaches opposition on the last day of the month. It is at its brightest at magnitude +5.7 but when viewed through a telescope, presents an apparent angular diameter of only 3.7 arc-seconds. Unfortunately, there is also a Full Moon on this night which will flood the sky with light so a telescope will be necessary to observe the green ice giant. The planet is visible all night as it is directly opposite to the Sun in the sky.

Neptune Aquarius

A small telescope is necessary to view the most distant planet in the solar system. Neptune is visible in the evening sky and is best viewed from the southern hemisphere.