SkyEye

The Calendar

Saturn's rings are at their most open this year. This coincides with quadrature, making the ringed planet a particularly tempting telescopic target this month. Can you see the shadow of the planet cast upon the rings?

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 Leo → Virgo

Observers in the southern hemisphere will have little luck seeing Mercury this month but the planet will be on show just before sunrise during the first few days of September for those in the north. Look for it very near the bright star Regulus on 5 September. At superior conjunction on 21 September, the closest planet to the Sun will reappear next month in the west at sunset.

Venus Virgo → Libra

The evening star heads back toward the western horizon but is still quite high as seen from southern latitudes. On the second day of the month, Venus appears less than 2° away from the first-magnitude star Spica. Later in the month, on 25 September, Venus reaches a magnitude of −4.6.

Earth and Moon

On 23 September, Earth reaches equinox. 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. In the northern hemisphere, the nearest Full Moon to the autumnal equinox is called the 'Harvest Moon'. This year, the 'Harvest Moon' occurs on 25 September.

The path of the Moon across the sky occasionally takes it in front of a first-magnitude star. On 3 September, just such an occultation occurs when the Moon obscures Aldebaran in the constellation of Taurus. This is the last in a series of 49 occultations which began in January 2015. The next Aldebaran series won't begin until August 2033. The next first-magnitude star to be occulted by the Moon will be Antares in 2023.

Mars Capricornus

Bright Mars continues to put on a good show for observers in equatorial and southern latitudes.

Jupiter Libra

Jupiter is high in the west at sunset when observed from the southern hemisphere but is getting increasingly difficult to view from the north.

Saturn Sagittarius

This is an excellent month in which to observe Saturn telescopically. The rings are at their most open as seen from Earth and Saturn reaches east quadrature on 25 September. It is at this time that the interplay of planet, moon and ring shadows are the most complex and interesting. Saturn reaches a stationary point on 6 September and resumes direct motion across the sky.

Uranus Aries

Uranus rises in mid-evening and is getting ever brighter as it approaches opposition next month.

Neptune Aquarius

A small telescope is necessary to view the most distant planet in the solar system. Opposition is on the seventh day of the month so this blue ice giant is aloft most of the night.