Eclipse

My luck held out and there were just enough gaps in the cloud to catch the start and maxima of the eclipse. It is pretty much solid cloud now, so I’m not going to see the moon leaving the sun.  I’ve taken about a dozen photographs of the progress of the moon across the sun – I’ll post them here when I’ve cropped and fiddled with them.

Solar Eclipse 2008

Today (if you are reading this in my tomorrow) or tomorrow (if you are reading this today) or at some point in the past (if you are reading this after tomorrow)
Scratch that – start again.

August 1st, 2008. Solar Eclipse. Moon passing in front of the sun, sky darkening, a bit like August 1999, except it will not get as dark (no totality visible from anywhere in the UK).

The NASA animation below shows a tiny black dot (in reality ~200km oval) shooting across the face of the earth – somewhere where this passes over is where you need to be to see a totally blacked out sun. At the time of maximum eclipse in London only ~12% of the sun will be occluded by the moon,the further north you live, the more of the sun will be occluded.

solar_eclipse_animate_2008-aug-01.gif

Seen from London, the edge of the moon will make contact with the sun at 9:33 AM (BST), maximum eclipse occurs at 10:18 and the whole show is over at 11:05 BST. There isn’t another Solar Eclipse visible from the UK until March 20th 2015.

That’s not all for the sky shows in August though. The Perseids Meteor Shower takes place between the 11th and 13th of the month – pick somewhere with dark skies and look up, predictions indicate this will be a good show.
There is also a partial eclipse of the Moon on the 16th August 2008. That’s when the Moon goes dark.On that date the moon is fairly low in the London sky and rising. It is only around 10 degrees above the horizon at maximum eclipse, so might be a challenge to see anyting unless you can get high up with a good clear view to the south east.

If you do plan to watch the solar eclipse do it safely.

Dark matter detected?

Dark matter is that weird stuff that is supposed to make up about 80% of all matter in the universe. It is invisible, and pretty much non-interacting (you can’t see it, and you can’t detect it (easily) by other means).

One way you might detect it is to take a very pure crystal and look for tiny flashes of light inside the crystal caused by a dark matter particle smacking into one of the atoms in the crystal. Nice idea, but insanely hard to do. For a start, natural radioactivity inside your crystal or your light detector will cause many more spurious flashes than there will be ‘real’ (caused by a head on collision of dark matter and an atom) flashes. You can then throw into that all the cosmic rays and particle showers caused by cosmic rays – these further add to the noise swamping the precious flashes of light signaling a dark matter hit (and your Nobel prize…)

You can get away from the spurious flashes somewhat, by building your crystal out of the most pure material you can get – filtering out a lot of the natural radioactivity, and then running the experiment deep underground – or in the centre of a local mountain – to filter out much of the cosmic ray noise.

What you should see now are random flashes of light, some of which might be caused by dark matter impacts, and the rest caused by all the crud you haven’t managed to filter. What you need now, is a way to differentiate the signal (dark matter) from the noise (radioactive crud).

These Italian researchers are claiming to have done just that.

The Sun and the solar system are moving (at around 250 km/sec) though a background of dark matter that fills the galaxy. The earth circles the sun at around 30km/sec, so for half of the year the velocity of the earth though the dark matter is 250+30 km/sec and for the other half of the year, the figure is 250-30 km/sec. This difference in velocity of the earth through the DM background should show up as a difference in the number of flashes of light in your detector – you hit more DM when you plow though it faster than when you move though it more slowly.


This rather stunning graph seems to show just that.

Ignoring the first part of the graph, where the detector wasn’t working at maximum sensitivity (so from 0 to about 3000 days on the bottom axis) and concentrating on the rest of the data, it really looks like the error bars show a sinusoidal variation with time – this is what the black line is fitting to. The data goes up and down once per year.
This type of variation is exactly what you’d expect from differences in the number of particles hit as the earth change velocity (speed and direction) though the DM background.

So, have they found Dark Matter? Or do they have another bug in the detector? Too soon to call on it yet, but this is very interesting.