In September, Jupiter is the most prominent planet in the night sky. Look towards the South just after sunset, and Jupiter is low in the sky. On 9 of September, the Moon can be seen just below Jupiter, acting as a convenient guide.
At this time of year, the Earth is on the side of the Sun which allows us to look up at constellations such as Hercules, Cygnus and Lyra.
In Cygnus, the star that makes up the head of the swan is called Alberio, a colourful double star in a small telescope.
In Lyra, another nebulae is visible through a small telescope – the ring nebula. Looking like a ring of smoke, it lies 1500 light years away. At the centre is a very hot white dwarf star emitting intense ultraviolet radiation, causing the ring to glow.
Directly overhead in the evening is a triangle of bright stars – Vega, Altair & Deneb. They are known as the summer triangle. Even though the trio appear to be of similar brightness to each other, in reality Deneb is much brighter. It is one of the brightest stars we know of, 250,000 times brighter than the Sun. It only looks as bright as Vega & Altair because it is 100 times further away. If it was as close as either, it would be as bright as the Moon!
Visible towards the North-West this month is the great globular cluster in the constellation Hercules. Through even a small telescope the sight is stunning. This cluster contains several hundred thousand stars, and lives on the very outskirts of our own Milky-way galaxy.
Look towards the North, and you can find the pattern of stars called the Plough (the tail and body of the constellation of the Great Bear, Ursa Major). The handle of the Plough points towards Arcturus, which can be remembered by the ditty “Follow the arc to Arcturus!”. Arcturus is a bright red-giant star, 16 times wider than our own Sun, and over 100 times brighter.
On Monday, the NASA/ESA Cassini spaceprobe flew just 30 miles (50km) over the surface of Enceladus, and at a staggering 40,000mph! Cassini took numerous images of the grooves that run along the moon’s south pole, where jets of icy water vapour erupt hundreds of miles into space.
To see the latest images, take a look at the Cassini flyby of Enceladus internet page, including the image below. For the thoughts of the Cassini scientists, see the Cassini blog.
On Saturday the 16th of August, we get to enjoy a lunar eclipse! A lunar eclipse occurs when the Moon goes into the shadow of the Earth.
It is no coincidence that we have a solar eclipse (when the Moon casts a shadow onto the Earth) and a lunar eclipse (when the Earth casts a shadow onto the Moon) just a fortnight apart…
Because the orbit of the Moon is tilted, it travels from the South of our flat solar-system to the North, and back South again every month. During the eclipse on the 1st of August, the Moon was travelling from the North down to the South… and as it did so it happened to pass in front of the Sun. On the 16th of August, the Moon is heading North again, passing though the shadow of the Earth on its way.
It is also no coincidence that we are having a pair of eclipse’s six months after the last pair! This is because the nodal axis of the lunar orbit happens to be in line with the Sun at the moment, which happens every six months because the Earth orbits the sun every year (see the graphic to the left, and my earlier post from the February eclipse season for more details).
This lunar eclipse will be visible from everywhere with the exception of the continent of North and central America (see this map). The animation I have created below using the excellent (and free!) Celestia software explains why the eclipse is not visible from the top half of the America’s… our planet gets in the way!
But for us here in the UK, the Moon will be rising in eclipse, so we have some tremendous and unique photographic opportunities to look forward to!
And what will the eclipse look like? Well, the Moon will turn either a deep red, a pink colour or maybe grey… we really don’t know! Take a look and find out for yourself! It all depends on the atmospheric conditions of the Earth at the time of the eclipse, since some sun-light will bounce through our atmosphere and illuminate the Moon even when it is in the shadow of the Earth.
The Moon will first enter the outer shadow of the Earth at 18:25 GMT (19:25 British Summer Time) – although, you may not even notice. An hour later, at 19:36 GMT (20:36 BST) the Moon begins to go into the dark heart of the Earth shadow, and that’s when the eclipse really begins!
The Moon is in the middle of the Earth’s shadow by 21:10GMT (22:10BST), and has left the dark shadow by 22:44 GMT (23:44 BST). The entire eclipse ends at 23:55 GMT (00:55 BST).
And for those of you too impatient to wait, below is a time-lapse movie of a lunar eclipse I saw back in March 2007! (click for full details).
The next week is the best time of the year to go looking for shooting stars (also called meteors). A shooting star is not actually a star at all, but a bit of dust. As that dust hits the Earth’s atmosphere, it burns brightly for just a fleeting moment, and we see it as a streak of light across the night-sky.
Next week is the best time of the year to look because the Earth just so happens to be going through the part of the solar-system that Comet Swift-Tuttle went through back in December, 1992. And that comet left lots of dust behind.
The Earth drives through this dust like a car driving through falling snow. So we get the best view of the meteors when we are on the ‘front’ of the Earth – that’s in the early morning. So the best time to see meteors this year is early morning on the Tuesday 12 August, when the Earth is at the heart of the stream of dust. Make sure you wait for the Moon to set as well, and get as far away from light pollution as possible – such light can drown out the view of all but the brightest meteors.
Comet Swift-Tuttle’s tail was quite wide, so we should see a larger number of meteors than usual for the next week. Click here to see the orbit of Comet Swift-Tuttle around our solar system.
The highlight this month is Jupiter, rising in the South-East at sunset before commuting towards the South-West overnight. Take a look through binoculars and you will be able to see up to four moons around the planet. Take another look just a few hours later, and you may notice that the moons have moved slightly in their orbit around Jupiter.
Every August, the Earth ploughs through dust and debris left behind by comet Swift-Tuttle – and this produces the Perseid meteor shower. It’s a bit like driving a car through snow fall, where the car is planet Earth, and the snow flakes are the bits of cometry dust, that burn brightly and briefly when they hit the atmosphere.
It’s called the Perseid shower because, during August, the Earth is moving towards the constellation Perseus as it orbits around the Sun at 70,000mph. So lots of meteors appear to be coming from that direction!
At this time of year, the Earth is on the side of the Sun which allows us to see constellations such as Hercules, Cygnus and Lyra. We are also on the side of the Sun that is nearer to the centre of our galaxy – so we get a great view of the Milky-way arching over head this time of year. But you will have to go somewhere dark to see it at its best, well away from any inefficient lighting.
In Cygnus, the star that makes up the head of the swan is called Alberio. Although it looks like a lone star to the unaided eye, a small telescope or binoculars reveals that this is actually a double star. It is the stark difference in colours that makes this double star such a delight. Although there has been no sign of any orbital motion of the last hundred years of observation, calculations suggest that they orbit around each other once every around 70,000 years! The pair are visible with a small telescope, so take a look.
I have to confess that I wasn’t expecting much from this eclipse! Sure, it’s always nice to see one, but it was only 22% coverage by diameter (12% by area) over London, we are at a solar minimum (so no sunspots were visible) and the weather forecast was looking uncertain. So would any one even turn up to the observatory to look? Would we get to see anything at all?
Any doubts I might have had, had totally disappeared by 9am! The Sun was shining, people were queuing up outside, and our volunteer helpers from the Flamsteed Astronomy Society were working flat out to set up all the telescopes. There was a fantastic buzz about the place – and the gates had not even opened yet!
From the moment the gates opened, the crowds were in, eager to know more about why eclipses occur, how frequently, how long do they last? And astronomers, both from the Flamsteed Astronomical Society and the Royal Observatory itself, were equally keen to answer all the questions.
And then the Moon began to hide the Sun.
Only a tiny amount at first, but enough for the children gathered to celebrate that they had all been the first to see the eclipse start! There is something magical about watching the Moon glide across the face of the Sun – you are seeing the Moon orbiting the Earth orbiting the Sun!
It may only be a small piece of the Sun hidden from view but it’s remarkable that it even happens at all. It was so wonderful to see the Sun, our nearest star, with a piece strangely missing that I had totally forgot about the lack of sunspots!
As the eclipse progressed, visitors to the Royal Observatory from all over the world, of all cultures and of all ages could be seen with smiling faces full of excitement and wonder.
It is always a thrill to see an eclipse, solar or lunar. So when is the next one? Well, we don’t have to wait long – there is a lunar eclipse in just 2 weeks time. And from the UK, the Moon will be rising in mid eclipse – perfect for some unique photography.
