SkyEye

The Calendar

The Harvest Moon lights up the sky two days before the equinox ushers in autumn in the northern hemisphere and spring in the south.

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 Leo → Virgo

The solar north pole is most inclined toward the Earth early this month.

Mercury Virgo

Mercury soars high above the western horizon this month for planet watchers in the southern hemisphere but remains at low altitude and virtually unobservable for astronomers in northern temperate latitudes. A third aphelion occurs on 6 September. The planet reaches greatest elongation east (26.8°) on 14 September; a week later it passes south of the first-magnitude star Spica. The tiny planet is losing altitude during the last half of September as it heads for an October rendezvous with the Sun. Mercury reaches a stationary point on 27 September and enters into retrograde.

Venus Leo → Virgo

The evening star is found in the company of a first-magnitude star this month, Spica, in the constellation of Virgo. Their closest approach occurs on the fifth day September. Venus is best viewed from the southern hemisphere where the bright planet, now shining at magnitude −4.1, is high in the west after sunset. For observers in northern temperate latitudes, however, Venus remains close to the horizon and sets an hour or so after the Sun.

Earth and Moon

Earth reaches its second equinox on 22 September. The word equinox means 'equal night' so that on this day, the (centre of the) Sun spends an equal amount of time above and below the horizon everywhere on the planet. Two days before that, the Harvest Moon illuminates the night sky.

Mars Leo → Virgo

The red planet is at conjunction early next month and soon vanishes in the glow of evening twlight.

Jupiter Capricornus

Jupiter is already aloft when the sky darkens and sets ahead of the dawn. It is best seen from southern latitudes.

Saturn Capricornus

Now past opposition, Saturn is easily visible during the evening hours. It sets after midnight but is best seen from the southern hemisphere where Capricornus rises high in the sky.

Uranus Aries

Once again the waning gibbous Moon closes in on Uranus, coming to within 1.3° of the faint planet. The green ice giant is rising in mid- to early evening and is best viewed from the southern hemisphere.

Neptune Aquarius

A small telescope is necessary to view the most distant planet in the solar system and this is the best time this year to observe Neptune. The blue ice giant is at its biggest (2.5 arc-seconds in apparent diameter) and brightest (magnitude +7.8) when it reaches opposition on 14 September. Appearing opposite the Sun in the sky, Neptune rises at sunset and vanishes at sunrise.