APOD 250,000

The Astronomy Picture of the Day account on Twitter has just reached quarter of a million followers with the 250,000th being @ZMWilmot (subject to a photo finish - thanks @staratlas). Every day all those followers around the world get a link to a stunning picture of the universe. All the nice comments from those people make all the effort of setting up the account and maintaining it since 2007 worthwhile. Of course, I just make sure the Twitter account gets updated. The real credit goes to Rob Nemiroff & Jerry Bonnell (the APOD curators), and the many people around the world who submit their images and videos.

† What is rather neat for me is that this is the second Twitter account I've started that has exceeded 250,000 followers. In neither case have I done marketing. They've succeeded by being interesting and having strong, existing, identities. The first account was @jodrellbank which I set up in 2007 and updated through the IYA until 2010 when I left Jodrell.

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Posted in astro blog by Stuart on Friday 30th Sep 2011 (16:27 BST) | Permalink

Agent Exoplanet

If you're a regular reader (one of the two) you'll know that I work for Las Cumbres Observatory Global Telescope. An aim of LCOGT is to help the interested amateur take their interest further and start to do their own scientific research. With that aim in mind, we decided to create a project for citizen scientists that focused on one of our areas of scientific interest. This first project - named Agent Exoplanet - takes you through the process of discovering the properties of exoplanets via the transit technique. It launched today.

Agent Exoplanet contains hundreds of images taken by LCOGT telescopes in California, Hawaii and Australia of planets orbiting their stars and blocking out a small fraction of the light. There are three planets included at the moment but we have a few more datasets nearly ready to add. I'll let LCOGT astronomer Rachel Street explain more in this video:

Early on the project needed a name (Planet Hunters got taken) and Agent Exoplanet ended up being the best name on our list. The name gave us a theme and we've had fun designing the interface to go with it. We've also tried to put some effort into explaining what to do with briefings, online tutorials and links to background information. Please try it out and let me know if you have any suggestions for improvements (remember it is for a fairly general audience).

Although we made this for exoplanets, the main part of the project infrastructre is simply about measuring lightcurves so is adaptable to other types of astronomical object. As an example, Ed dumped in our public observations of the supernova in M51 during the summer and we quickly had the lightcurve which surprised us as it was still rising. That was pretty exciting and showed us that it worked!

This has been our first major project like this but it won't be the last. We have more ideas...

Posted in astro blog by Stuart on Monday 26th Sep 2011 (21:39 BST) | Permalink

Speed limits - check your distance

It has been an exciting 24 hours since it became clear that the OPERA experiment at Gran Sasso in Italy may have detected neutrinos travelling faster than light. If this measurement is true, it would appear to break a fundamental part of Special Relativity that states that matter can't go faster than light. Physicists (including the ones making the announcement) are being cautious as dramatic claims require dramatic evidence.

What exactly is claimed? Well, one of the experiments at CERN in Switzerland smashes protons into a graphite target. Those collisions produce mesons that then decay into muons and neutrinos. The muons get detected at CERN. The neutrinos hardly interact with matter so stream merrily* away from the experiment through the Earth's crust. Nearly all of those neutrinos will pass through the crust and stream out into space just like the billions of neutrinos from the Sun that pass through our planet every second. A team of particle physicists then placed a detector in central Italy that sits in the path of those neutrinos to catch some of them.

Over the past few years the OPERA team have precisely measured the distance between the source of neutrinos in CERN and their detector in Italy. They have also measured the time it takes between the production of the neutrinos and their arrival at their detectors. They have made some amazingly precise measurements and there are some really neat aspects to this work such as creating modulated bunches of protons and seeing identical profiles in the detected neutrinos at the other end.

Dividing the distance by the time taken gives velocity. When they put the numbers in it seems to be faster than light. They think the neutrinos arrived 60 ns (+/- 6.9 ns from statistical and +/- 7.4 ns from systematic uncertainties) quicker than photons would have. That means they travelled about 1.000025 times faster than the speed of light. Wow!

As an astronomer I know there are some problems with this claim because a previous test did not show the same result. Back in 1987, neutrinos from the famous supernova SN1987a were detected after astronomers saw it (Update 24 Sep 10:41 BST: I shouldn't have written all this so late at night. In fact, the neutrinos were detected 3 hours before the light. Peter Coles says: "The few hours delay between neutrinos and photons is explained by the fact that neutrino emission occurs when the core of the progenitor star collapses, whereas visible light is released only when a shock wave reaches the surface of the imploding object"). Those neutrinos had not travelled faster than light. As Peter Coles says, if they had been travelling faster than light they would have arrived a few years earlier given the massive distance involved. The SN1987a result put a more precise limit on the speed of neutrinos which doesn't agree with this OPERA result. The OPERA paper does acknowledge the SN1987a measurements and notes that they were at a much lower energy - 10 MeV compared to 17 GeV. To make them both agree, the faster-than-light ability would have to be energy dependent. That is possible.

It is also possible (and as an experimentalist, I'd say more likely) that there are some subtle effects that they have not accounted for in their experiment. Ultimately there could be an error in their timing or in their distance. From what I caught of the web-cast (I didn't see all of it as I had work to do) their timing is very good so my hunch is on the distance measurement. It only has to be wrong by 18 m for the result to disappear.

They have used GPS receivers to get very precise positions and I don't doubt that. It is much more accurate than 18 m and their claim of 20 cm sounds plausible. However, the GPS receivers need to see satellites so the very precise positions are for locations on the surface. The source and detector are deep underground though. Using other means they've had to work out where their experiments are relative to those points on the surface. Unfortunately, they don't go into much detail about how those final distances (and directions) were determined.

This afternoon Chris North, Bob Watson, and I had a discussion about things that could affect their measurement of separation. They may have determined their distance vertically and assumed that "vertical" meant "towards the centre of the Earth" (or towards the centre of the ETRF2000 reference frame). However, that is not always true. Local concentrations of mass near the surface of the Earth will slightly alter this because there will give a component of gravity sideways. A large mountain to one side of you could alter "up" such that going 1.4 km "down" could actually move you off a geometric line to the centre of the Earth by a few metres (Update 24 Sep 11:41 BST: probably less than a metre over 1.4 km). If there was a mass concentration to the north, it would deflect "down" towards the north and you'd be a little closer to CERN than you thought at the bottom of your tunnel. The OPERA experiment does happen to sit to the south of the mountain Gran Sasso.

The physicists at OPERA may have taken the vertical deflection into account. If they haven't it will be a source of systematic uncertainty.

* Please forgive the anthropomorphism.
† An under-statement
‡ I am aware that ETRF includes "reference frame"

Posted in astro blog by Stuart on Saturday 24th Sep 2011 (01:26 BST) | Permalink

Circumbinary planet Kepler-16 (AB)-b

Astronomers using Kepler data have found a planet orbiting two stars. I did see the news on Twitter last night but it was only when I read the journal paper this morning that I got really interested in this announcement.

Artists impression of the Kepler-16 system. CREDIT: NASA/JPL-Caltech/R. Hurt
Over the past week we've had a slew of planet announcements including: 50 candidates discovered with HARPS (on the VLT) on Monday; 23 discovered with WASP on Tuesday; and another 7 announced since yesterday. The discoveries this week have been due to astronomers saving up announcements for the Extreme Solar Systems conference in Wyoming. They've taken the total number of exoplanet candidates up to 684! Will we reach 1000 by the end of the year?

This new system is remarkable because it is the first planet found to orbit a double star system. This is really helpful because it provides many different types of transits (each of the stars transiting each other as well as transits involving the planet) and these allow absolute values for the properties of the system. Normally a transit provides the relative sizes of the star and planet and you then have to use stellar evolution models to estimate the mass of the star and get the absolute sizes.

The paper establishes that the system contains 0.2 and 0.7 solar mass stars that orbit around a common centre of mass every 41 days. They are, in turn, orbited every 229 days by a planet with about 0.33 the mass of Jupiter and about 0.75 the radius of Jupiter.

The stars are separated by about 0.2 AU and the planet's orbit is 0.7 AU so the planet will experience temperature variations depending on which star is closer. Based on models of the star types, it is estimated that the temperature ranges from about 170 - 200 K so this will be a pretty cold world unlike Tatooine. They calculate a mean density close to water but say (based on models of planetary interiors and estimates of the planet's age) it is likely to be about half gas (hydrogen/helium) and half heavier elements (rock/ice?).

They were fairly lucky to spot this system when they did. The inclination of the planet's orbit varies. If their models of the orbit are correct, we will not see a transit of the second star from 2014-2049 and we won't see the planet transit the larger star from 2018-2042. So, if Kepler had suffered a 10 year delay to launch it would never have seen this system during its 3.5 year mission and may have had to wait until the mid 21st century to know about it.

Congratulations to everyone who has announced planet discoveries in the past week or two.

Update 13:56 BST: Rob Simpson has pointed out that citizen scientists on Planet Hunters may have spotted this planet 4 months ago. Very cool.

Posted in astro blog by Stuart on Friday 16th Sep 2011 (12:34 BST) | Permalink

Comet Elenin

There seems to be an increasing amount of rubbish being banded around the interwebs about Comet Elenin. Much of this seems to be driven by the 2012-ers who are connecting it with the made-up planet "Nibiru". The 2012-ers are promoting the idea that Elenin will crash into the Earth and/or cause massive destruction. There have even been some claiming Elenin is already responsible for the Japanese earthquake even though it wasn't.

The first I noticed of this Elenin-related rubbish was last week when I stumbled across elenin.org. That webpage starts off sounding quite reasonable but quickly starts making up "facts" such as Elenin having a "3,600 year orbit around the galaxy". As the Solar System is about 30,000 light years from the centre of the Galaxy, Elenin would require a speed many times the speed of light to get around that fast! Just a little bit in excess of the "85,000 km/hr" they quote for Elenin's speed. There are many other nonsensical statements to spot on that site.

The awful thing is that the 2012-ers are worrying others. A concerned student came to our office today to ask about Comet Elenin. Someone had told him to leave Cardiff and go home because "terrible things will happen". Chris tried to tell him the facts and reassure him that there was nothing to worry about from Elenin. As with many who have heard a conspiracy, actual facts are unlikely to convince him and may even re-enforce it. Sigh. Roll on 2013.

There is genuine information and images about Elenin on the Armagh Planetarium blog.

Posted in astro blog by Stuart on Monday 05th Sep 2011 (15:22 BST) | Permalink
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