Halloween’s approach and passing marks the time of year when a ghostly figure is best visible in our evening sky.
Early morning viewers may have been enjoying many hours of possible sightings since late June, but at this time of year, prime viewing time for the most distant object visible to the naked eye moves to midnight and the hours either side.
On a clear night, looking north from a dark country location with no Moon, you can gaze across unimaginable vastness to see the Andromeda Galaxy (M31). It is ghostly and difficult to see, appearing as a faint smudge against the darkness of space. Binoculars will make the task easier. Be aware that, when you find it, no view taken in by the human eye can compete with the extraordinary long exposure photographs gracing today’s media – YET – there is often a spine-tingling sensation that comes with the appreciation that you’re actually seeing a thing SO big, SO remote and SO old, with your own eyes!.
M31 is the large spiral galaxy ‘next door’ to our own Milky Way Galaxy (also a spiral – a barred spiral to be precise). Galaxies are essentially ‘cities of stars’ that come in all shapes and sizes of which spirals are arguably the most beautiful.
Many people will be familiar with the soft glow of our Milky Way which we sometimes see stretching from horizon to horizon. This ‘glow’ is the combined light of many billions of stars inhabiting the regions towards our galaxy’s centre. Our Sun is of course a star whose home is in one of the spiral arms of the Milky Way. As such, we live in the outskirts, one of the Milky Way’s suburbs if you like, with every individual star visible to the unaided eye being a member of our local suburb.
We’re privileged to be able to look through our suburb and beyond our city centre (of stars) to glimpse the fleeting old light of the next major ‘city’. This light is old because Andromeda is 2.5 million light years away, so when we glimpse it, we see it as it was 2.5 million years ago.
Once thought to be about twice the diameter of our Milky Way, recent studies have indicated that our nearest neighbour might be the about same size. Still, at 800 billion solar masses, neither galaxy can be considered light-weight. And though M31 looks peaceful, astronomers have uncovered a violent past and future. Many billions of years ago, in separate events, evidence suggests that two dwarf galaxies were consumed by it. Several billion years from now it is thought that Andromeda will collide with our own Milky Way. Worth waiting for.
How do we find it? Looking north we find a large box of four stars called the Great Square of Pegasus. The constellation Andromeda runs off the lower eastern corner of the Great Square and if you trace that line and slightly east you should find it. This free starchart may be helpful.
Unfortunately, from our latitudes it never rises high above the northern horizon so is seen best from northern New Zealand. Sorry southerners!
Early November is ‘potentially’ a great time for viewing in the late evening, but this year we’ll have to allow for a waxing crescent Moon as it begins to invade the sky from the west early in the month. It will move nightly eastward until it retires as a waning gibbous Moon to the eastern horizon mid-month giving us a couple of weeks of further opportunity. As we move toward the longer December days, we’ll need to wait for the sky to darken, and all too soon the Moon will return. Then as December progresses, the long daylight hours will be an issue, and our object will be lost to the daylight until the return of winter’s early mornings.
So the advice is, start looking for it now, in October, before the Moon confounds your efforts!
This binocular image (right) is what we would expect to see from the northern hemisphere. From our southern latitudes we are looking through more atmosphere so our view will not be as distinct. We also need to hold the page up-side-down!
After all this hard work chasing the M31 apparition you might appreciate an easier target, and if so, we have just the thing for you. The brilliant planet Venus has already taken up its post as the ‘evening star’. Of course, it is NOT a star (see image above left), but this description persists!.
The following chart depicts the shape of the planet as seen through a telescope and where it can be found over the ensuing months. The dashed line is the celestial equator. At the time of writing the planet is very far away on the opposite side of the Sun so we’re seeing it in virtually full ‘phase’. By way of explanation, since they are closer to the Sun than Earth, both Venus and Mercury appear to go through phases much like the Moon. This is because we can only see their sunlit portions. By April/May Venus will be catching up with Earth on the near side of the Sun then appearing as a much larger waning crescent.
Venus is the third brightest object in the sky exceeded in brilliance only by the Moon and the Sun. It can be so bright that its appearance often prompts phone calls and emails from curious public. It will be at its most brilliant in mid-autumn as it heads back down towards the Sun. Those with sharp eyes who know where to look may even be able to pick it out in broad daylight. However, it looks its stunning best when high in the sky against the very dark blue of the ‘almost’ night.
Enjoy your summer evenings.
John Rowe, Astronomy Educator
Top left – Venus’ surface is shrouded by clouds composed largely of sulfuric acid droplets. These clouds reflect most of the sunlight falling on them giving the planet its brilliance
Top right – The Binocular Sky
Bottom – Guy Ottewell via his blog
Front blog tile: NASA