Shropshire Sky At Night – September

The September equinox occurs at 20.11 BST, when the sun will shine directly on the equator and there will be nearly equal amounts of day and night throughout the world. From then onwards the evenings become darker, and what better objects to entice us to the eye piece than the planets of the Solar System.

Although Mercury will be difficult to spot even on the 14th when it reaches its greatest eastern elongation, Venus shines bright all month as an ‘evening star’, visible soon after sunset. You will need a clear south west horizon as it does not rise too high into the sky.

Sadly the red planet, Mars, is not visible as it is heading to next month’s conjunction with the sun. Both Jupiter and Saturn remain beacons in the evening skies, Jupiter climbing in the south-eastern skies, its retrograde motion puts it into the constellation of Capricornus, while Saturn provides excellent evening views.

Since Earth orbits the sun at different speeds than the other planets, when we overtake these other planets they appear to move backward in the sky. This optical illusion, which we refer to as retrograde motion, happens more frequently with inner planets like Mercury, which orbit the sun quicker than other planets like Saturn and Neptune.

The ice giant Uranus becomes a viable target close to midnight around the middle of the month, with a pair of binoculars revealing its location in southern Aries. Neptune, the most distant planet from the sun, comes into opposition on 14th. A small telescope (four or six inches class) with a magnification of around 100 times will identify its green blue disc passing along the boundary between Aquarius and Pisces.

The Full Moon on the 20th is referred to as the Harvest Moon, as it is the full moon that occurs closest to the September equinox. However the New Moon on the 7th is the best time of the month to observe faint objects.

These include planetary nebulae which are the result of expanding shells of luminous gas expelled by dying stars. Despite their name, they have nothing to do with planets, and were so named because early astronomers thought they looked a bit like planets through a small telescope.

Two such targets within easy reach of the novice stargazer are the Dumbbell Nebula or Apple Core Nebula, in the constellation of Vulpecula. It is large and quite bright, which makes it a popular object among amateur astronomers. It can be seen in binoculars and small telescopes.

The Helix Nebula is located in the constellation Aquarius and is one of the closest to the Earth of all the bright planetary nebulae. Given clear skies one should be able to spot it using a three or four inch class telescope operating at low magnification.

Our picture showing the Dumbbell Nebula (left) and Helix Nebula by local amateur astronomer Andy Gannon illustrates what can be achieved from the dark skies of South Shropshire.

Steve Szwajkun FRAS is chairman of Shropshire Astronomical Society