Sunday, 20 March 2011

Celestial bodies and the oddities of their motion

Here is a picture of the sky some minutes after sunset on 19th March 2011, looking west across the city of Norwich. Actually it is a combination of 16 pictures through the 135mm lens on the Canon 350D. I didn’t combine in the usual way by pinning the stars down, but by just placing one on top of the other and each time just choosing the lighter of the two pixels from above or below. The result, I hoped, would tend to minimise the cloud by preferentially letting the lighter sky through. Luckily the camera was very still on its tripod through this period in which I was graced with a passing interested chap who had popped home to bring his wife along, at which point a plane decided to make my picture sequence a little more interesting. I wonder whether the crew and passengers knew that they were passing so close to the planet Mercury, the upper “star” and whether it looked like a huge bright ball out of their windows. I jest of course.
The 16 pictures show the even descent of Mercury and Jupiter (the lower “star”) at the angle of <37.5º caused by the earth’s rotation. Mercury is at its widest separation left or west of the sun and the plane of its orbit pokes up northward from our perspective at spring dusk making it higher for us in the northern hemisphere. Mercury at this point is the same distance as the sun. On the other hand, we are waving bye bye to Jupiter as it is way beyond the sun and so is ‘sinking rapidly into the twilight’. The twilight is getting earlier as we approach summer, and the orbit of the Earth is moving so that the sun appears to approach Jupiter, which looks as bright as Mercury, but is 6 times further away. Mercury is moving more rapidly around the sun (88 days long is its year), so it appears to move with the sun and will stick around for a few more days, until it decides to pop up in the dawn sky for those nearer the southern hemisphere. While all this is happening in a darkening sky, I can see the Orion Nebula, Sirius the Dog Star, and in the cold wind the so-called supermoon is rising behind me. The closest point of its orbit has happened to coincide with full moon as it’s swinging around us on Earth. From my perspective on this rotating spheroid, Jupiter had disappeared and been replaced with a very bright patchy grey face shining through the trees. Naked-eye astronomy is pretty inspiring sometimes.

The supermoon is doing weird things to us all

It’s so bright!!!!! Ahhhhh! There are a lot of weird things being suggested about the supermoon. Crazy tides (well slightly bigger tides, yes that’s true). But the spate of disasters? No. Nor is it anything to do with the end of the world in 2012. It is just the moon… a little bit closer to Earth than usual… and at full moon… Still, there’s always fear of the unknown…. Aaaah! Panic! Technicially it’s the brightest moon for years, but by the tiniest amount. The same went for Mars in 2003. The word for the closest point on an orbit around Earth is perigee, and the furthest, apogee (geo-). This goes for the sun: perihelion and aphelion. Also, any lunar probes would have an periselene & aposelene. A bit like an apex. In these pics the moon is at perigee and 356 577 km away. Canon350D ISO400 135mm f/2.8 10”, plus f/16 1/640” for detail.

Sunday, 13 March 2011

Modified EOS 1000D vs EOS 350D

Here is the crab nebula, a supernova remnant that exploded in 1054AD(our time), and was witnessed as the ‘daylight star’ in China. It is a nice target to image for a test, as it contains red filaments surrounding a blue cloud. The red light comes from “hydrogen balmer alpha”, which means an electron in an excited atom of hydrogen drops from quantum level 3 to level 2. The blue light mostly comes from “hydrogen balmer beta”, which is from 4 to 2, a larger drop in energy giving a more energetic photon of light, i.e. a ‘blue’ photon is more energetic than a 'red' one. The purposes of “modifying” a new 1000D (thanks dslrastromod) is to enable most of that alpha light to get to the camera sensor. Roughly 4 times as much. You can see that effect here in this before and after shot. It’s not a proper comparison as the first one was about 10 x 30 second pictures on a 350D, and the second was 6 x 1 minute pictures and both could have been taken with different background brightnesses. But I think you can work out how pleased I am to have improved my astronomical capabilities by such a large jump.

Wednesday, 2 March 2011

Blip… there goes another star.

I remember being shown this amazing object for the first time in a new 12 inch Dobsonian at Norwich Astronomy Society by a guy who knew his way around the sky and had just hunted this thing down. There was quite a queue after quite a quirky astronomical quest. This object lies in the constellation of Cassiopeia - the Queen of Ethiopia, and you would think it easy to find: "just past the ‘W’ shape, to 4 Cas, then across a bit, past the cluster M52"… but I can never find the damn thing by star-hopping. On this occasion I had the luxury of a computer, which takes the challenge out of it, but my sky knowledge is useful every time there is a system error. With autoguiding on the star in the frame above, the position of this object in the sky allowed 1 minute exposures before too much rotation occurred. A few of these later, I revealed the blue bubble cast out by the star’s stellar wind, set against the surrounding interstellar redglowing hydrogen. There is also the strange, pinkish bar close by the central star, which is itself offset slightly from the centre of the bubble. It looks like this enraged star is hurtling along while blasting away 10 light years of space around it (that’s a 30 million million mile radius) with its fierce radiation.

'Icy' 348

By the star Atik, in the constellation of Perseus, hides this faint reflection off interstellar dust. It is now thought that Atik is not associated with this reflection and that the cluster within it, IC 348, lights it up. Giving a very icy visual impression the reflection nebula is on the other side of the cloud I showed you in the last post. The dazzlingly bright Atik looks so much closer to us than the nebula but you must bear in mind stars have a vast range of luminosities. While it is visible as a shimmering point of light here, and to the naked eye above the Pleiades in the autumn, winter and spring, the star is actually two - a blue giant, with a blue dwarf orbiting it in 4 ½ days that mutually distort each other into rugby ball shapes. And the larger is indeed luminous, as it is probably a good deal greater than 1000 light years away AND it has dust in the way. Otherwise known as just plain old ‘omicron Persei’, Atik is referred to in a certain fictional account as having a system of planets surrounding it, colonised by a race of giant horned toad creatures, where the 8th planet is ruled by the despotic leader, Lrrr.