September 2017

Welcome to SkyEye, your guide to this month's celestial events.

The Calendar

Date Event
Thursday 1
Friday 2
Saturday 3
Sunday 4
Monday 5 Neptune at opposition
Tuesday 6 The Full Moon occults Neptune: visible from the Antarctic and southern South America, and beginning around 04:00 UT.
Wednesday 7
Thursday 8
Friday 9
Saturday 10
Sunday 11
Monday 12 Mercury at greatest elongation west
Moon occults first magnitude star Aldebaran: visible from Hawaii and the west coast of North America, and beginning around 10:30 UT.
Tuesday 13 Last Quarter Moon at the farthest perigee of the year
Wednesday 14 Saturn at east quadrature
Thursday 15
Friday 16
Saturday 17 Moon occults Venus: twilight and daytime event
Sunday 18 Moon occults first magnitude star Regulus: twilight and daytime event
Moon occults Mars: twilight and daytime event
Moon occults Mercury: twilight and daytime event
Monday 19
Tuesday 20 New Moon
Wednesday 21
Thursday 22 Earth at 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.
Friday 23
Saturday 24
Sunday 25
Monday 26
Tuesday 27 Moon at apogee
Wednesday 28 First Quarter Moon
Thursday 29
Friday 30

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 LeoVirgo

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

Mercury LeoVirgo

Now a morning sky object, Mercury rises quickly early in the month and then sinks back down just as fast from a northern vantage point. For southern observers, the closest planet to the Sun remains low in the east before sunrise all month. On 12 September, Mercury reaches greatest elongation west and six days later it is the last of four bright objects (three planets and one star) to be occulted by the Moon.

Venus CancerLeo

The morning star is best seen from northern latitudes this month, high above the eastern horizon before sunrise. It is much lower in the sky as viewed from the southern hemisphere and is slowly losing altitude. Beginning around 22:00 UT on 17 September, Venus is occulted by the Moon as seen from the Indian Ocean.

Mars Leo

Mars emerges from the morning twilight around mid-month. Along with Mercury and Venus, the red planet is occulted by the Moon on 17/18 September.

Jupiter Virgo

Jupiter is getting increasingly difficult to observe as it heads towards conjunction next month.

Saturn Ophiuchus

Saturn will be a east quadrature on 14 September. This is an excellent time to observe and photograph the planet as the shadows of the planet's disc, rings and moons are all cast maximally off to one side, lending an interesting three-dimensional effect to the scene. It is best observed from southern latitudes where it doesn't set until late evening. The following day at 10:44 UT, the spacecraft Cassini will plunge into Saturn's atmosphere. Launched on 15 October 1997 from Cape Canaveral Air Force Station in Florida, the spacecraft spent 13 years orbiting Saturn, far exceeding its original four-year mission plan. The data returned by Cassini has revolutionised our understanding of Saturn, its ring and its moons. Farewell, Cassini!

Uranus Pisces

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 fifth day of the month so this blue ice giant is aloft most of the night. The southern regions of South America (and parts of Antarctica) may see this planet occulted by the Moon on the following day.

The Celestial Sphere

Constellations are patterns of stars in the sky. The International Astronomical Union recognises 88 different constellations. The brightest stars as seen from the Earth are easy to spot but do you know their proper names? With a set of binoculars you can look for fainter objects such as nebulae and galaxies and star clusters or some of the closest stars to the Sun.

Descriptions of the sky for observers in both the northern and southern hemispheres are available for the following times this month. Subtract one hour from your local time if summer (daylight savings) time is in effect.

Local Time Northern Hemisphere Southern Hemisphere
1730 hours (1830 hours summer time) 45° N 30° S
1930 hours (2030 hours summer time) 45° N 30° S
2130 hours (2230 hours summer time) 45° N 30° S
2330 hours (0030 hours summer time) 45° N 30° S
0130 hours (0230 hours summer time) 45° N 30° S
0330 hours (0430 hours summer time) 45° N 30° S
0530 hours (0630 hours summer time) 45° N 30° S