SkyEye

The Calendar

The 'Harvest Moon' (the full Moon nearest to the northern hemisphere autumnal equinox) is on 14 September. It appears smaller than usual, as it also is this year's 'Micro Moon'.

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

Mercury is at superior conjunction on 4 September and is not on view until later in the month when it appears low in the west after sunset. Mercury and Venus have a close encounter on 13 September and Mercury skims past Spica on the penultimate day of the month. Mercury is much fainter than Venus but somewhat brighter than Spica.

Venus Leo → Virgo

The two inferior planets have a very close appulse on 13 September when they come within 0.3° of each other. This will be difficult to observe as both planets were recently at superior conjunction and are still very near to the Sun. The southern hemisphere has slightly better views of the evening star, low in the west after sunset.

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. In the northern hemisphere, the nearest Full Moon to the autumnal equinox is called the 'Harvest Moon', and this year, it occurs on 14 September. This Full Moon also occurs only 15 hours after apogee, resulting in a so-called 'Micro Moon'.

Mars Leo → Virgo

Mars is at conjunction on 2 September and is not visible for most of this month. It eventually reappears in the morning sky.

Jupiter Ophiuchus

Jupiter reaches east quadrature on 8 September. This is an excellent time to observe the gas giant through a telescope where the shadows cast by the planet and its large moons are seen off to one side. Northern hemisphere viewers will be hard-pressed to see Jupiter as it sets early in the evening, but observers in tropical and southern latitudes have a little longer to watch the magnitude −2.1 planet.

Saturn Sagittarius

Another lunar occultation occurs this month when, on 8 September at about 11:15 UT, the waxing gibbous Moon passes in front of Saturn. Ten days later, Saturn reaches a stationary point and returns to direct or prograde motion across the sky. The ringed planet dims to magnitude +0.5 this month and is best seen in the evening skies from the southern hemisphere.

Uranus Aries

With opposition occurring next month, Uranus is rising ever earlier before midnight. Southern and tropical regions still get the best views of this sixth-magnitude planet.

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 10 September, the blue ice giant is at its brightest (magnitude +7.8) and is visible all night. Earlier in the month, Neptune passes near the fourth-magnitude star φ Aqr.