SkyEye

The Calendar

Both the Harvest Moon and Jupiter (at opposition late in the month) light up September 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 Leo → Virgo

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

Mercury Virgo

Still an evening sky object for much of the month, Mercury enters into retrograde motion two weeks before inferior conjunction on 23 September. It returns to the east at dawn but may still be too close to the Sun on 26 September when it is 3.2° south of the much brighter Venus.

Venus Virgo

Venus reaches perihelion on the fourth day of the month. Its close proximity to Mercury on 26 September is a sure sign that conjunction with the Sun is nearing. Look for the morning star low in the east at dawn.

Earth and Moon

Earth reaches its second equinox on 23 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. The Full Moon nearest to this equinox is called the Harvest Moon and this year it occurs on 10 September. A lunar occultation of Uranus takes place four days later.

Mars Taurus

The red planet finally rises before midnight for southern hemisphere observers but it does not gain any useful height until the morning hours. Northern latitude planet chasers are favoured when it comes to spotting this increasingly bright orb moving through the constellation of the 'Bull'.

Jupiter Cetus → Pisces

Jupiter finally reaches opposition on 26 September. It shines a brilliant magnitude −2.9 in the otherwise faint constellation of Pisces and measures 49.8 arc-seconds across in apparent diameter. It is visible all night around the end of the month.

Saturn Capricornus

Now past opposition, Saturn is an evening sky object, already above the horizon as the sky turns dark. It sets in the early morning hours.

Uranus Aries

Uranus rises mid-evening this month. It is occulted by the waning gibbous Moon on 14 September, beginning around 21:00 UT and visible from northern Africa, Europe, western Asia, Iceland and Greenland.

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. At opposition on 16 September, the blue ice giant is at its brightest at magnitude +7.8. A telescope reveals a disk just 2.5 arc-seconds across. Look for this planet at any time during the night; it rises around sunset and sets about sunrise.