Archive for European Space Agency

Euclid’s Flagship Simulation

Posted in The Universe and Stuff with tags , , on July 28, 2017 by telescoper

 

Credit: J. Carretero/P. Tallada/S. Serrano for ICE/PIC/U.Zurich and the Euclid Consortium Cosmological Simulations Science Working Group.

The above image is taken from the world’s largest simulated galaxy catalogue, which has been constructed to help prepare for the  forthcoming Euclid space mission. The image actually shows only a small part of the full Euclid Flagship mock galaxy catalogue, which contains more than 2 thousand million galaxies distributed over the 3-dimension cosmological volume that Euclid will survey. Synthetic galaxies in this simulation mimic with great detail the complex properties that real sources display: ranging from their shapes, colours, luminosities, and emission lines in their spectra, to the gravitational lensing distortions that affect the light emitted by distant galaxies as it travels to us. The simulation is large enough to allow full `light-cone’ effects to be taken into account, as the look-back time to the edge of the Euclid survey volume is long enough for significant evolution to have occurred; according to the standard cosmological model, the time taken for light to travel from redshift z=2.3 to now is about 10.8 billion years, a significant fraction of the age of the Universe.

`Mock’ catalogues like this are needed to plan large observational programmes, whether using space missions or ground-based facilities, and to help prepare the data analysis strategies and tools needed to deal with the real data when it arrives. They can also be used to make excellent images for PR and outreach purposes.

The use of the word `simulation’ always makes me smile. Being a crossword nut I spend far too much time looking in dictionaries but one often finds quite amusing things there. This is how the Oxford English Dictionary defines SIMULATION:

1.

a. The action or practice of simulating, with intent to deceive; false pretence, deceitful profession.

b. Tendency to assume a form resembling that of something else; unconscious imitation.

2. A false assumption or display, a surface resemblance or imitation, of something.

3. The technique of imitating the behaviour of some situation or process (whether economic, military, mechanical, etc.) by means of a suitably analogous situation or apparatus, esp. for the purpose of study or personnel training.

So it’s only the third entry that gives the meaning intended to be conveyed by the usage in the context of cosmological simulations. This is worth bearing in mind if you prefer old-fashioned analytical theory and want to wind up a simulationist!

In football, of course, you can even get sent off for simulation…

LISA gets the go-ahead!

Posted in The Universe and Stuff with tags , , , , , on June 21, 2017 by telescoper

Just taking a short break from examining duties to pass on the news that the European Space Agency has selected the Laser Interferometric Space Experiment (LISA) – a gravitational wave experiment in space – for its large mission L3. This follows the detection of gravitational waves using the ground-based experiment Advanced LIGO and the success of a space-based technology demonstrator mission called Lisa Pathfinder.

LISA consists of a flotilla of three spacecraft in orbit around the Sun forming the arms of an interferometer with baselines of the order of 2.5 million kilometres, much longer than the ~1km arms of Advanced LIGO. These larger dimensions make LISA much more sensitive to long-period signals. Each of the LISA spacecraft contains two telescopes, two lasers and two test masses, arranged in two optical assemblies pointed at the other two spacecraft. This forms Michelson-like interferometers, each centred on one of the spacecraft, with the platinum-gold test masses defining the ends of the arms.

Here’s an artist’s impression of LISA:

This is excellent news for the gravitational waves community, especially since LISA was threatened with the chop when NASA pulled out a few years ago. Space experiments are huge projects – and LISA is more complicated than most – so it will take some time before it actually happens. At the moment, LISA is pencilled in for launch in 2034…

New: Top Ten Gaia Facts!

Posted in Astrohype, The Universe and Stuff with tags , , , on September 14, 2016 by telescoper

After today’s first release of data by the Gaia Mission, as a service to the community, for the edification of the public at large, and by popular demand, here is a list of Top Ten Gaia Facts.

Gaia looks nothing like the Herschel Space Observatory shown here.

Gaia looks nothing like the Herschel Space Observatory shown here.

 

  1. The correct pronunciation of GAIA is as in “gayer”. Please bear this in mind when reading any press articles about the mission.
  2. The GAIA spacecraft will orbit the Sun at the Second Lagrange Point, the only place in the Solar System where the  effects of cuts in the UK science budget can not be felt.
  3. The data processing challenges posed by GAIA are immense; the billions of astrometric measurements resulting from the mission will be analysed using the world’s biggest Excel Spreadsheet.
  4. To provide secure backup storage of the complete GAIA data set, the European Space Agency has commandeered the world’s entire stock of 3½ inch floppy disks.
  5. As well as measuring billions of star positions and velocities, GAIA is expected to discover thousands of new asteroids and the hiding place of Lord Lucan.
  6. GAIA can measure star positions to an accuracy of a few microarcseconds. That’s the angle subtended by a single pubic hair at a distance of 1000km.
  7. The precursor to GAIA was a satellite called Hipparcos, which is not how you spell Hipparchus.
  8. The BBC will be shortly be broadcasting a new 26-part TV series about GAIA. Entitled WOW! Gaia! That’s Soo Amaazing… it will be presented by Britain’s leading expert on astrometry, Professor Brian Cox.
  9. Er…
  10. That’s it.

Gaia’s First Data Release!

Posted in The Universe and Stuff with tags , , , on September 14, 2016 by telescoper

It seems like only yesterday that I was blogging excitedly about the imminent launch of the European Space Agency’s Gaia Mission. In fact it was almost three years ago – 1000 days to be precise – and today the world of astronomy is a-flutter with excitement because we’ve just seen the first release of data from the mission. You can find an overview with links to all the yummy data here. I can’t resist pointing out the adoption of a rigorously Bayesian method for dealing with partial or incomplete data when a full astrometric solution is not possible due to insufficient observations. If you want to go straight to the data archive you go here or you could try one of the other data centres listed here. It’s great that all this data is being made freely available, but this is only the first set of data. It’s just a hint of what the mission overall will achieve.

If you would prefer some less technical background to the mission have a look here.

Here’s a summary (courtesy of ESA) of what Gaia has achieved so far:

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There’s much more to Gaia than pictures, but here’s the first map of the sky  it produced:

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I remember first hearing about Gaia about 15 years ago when I was on a PPARC advisory panel and was immediately amazed  by the ambition of its objectives. As I mentioned above, Gaia is a global space astrometry mission, which will make the largest, most precise three-dimensional map of our Galaxy by surveying more than a billion stars; DR1 is really just a taster as the measurements will become more complete and more accurate as the mission continues.

In some sense Gaia is the descendant of the Hipparcos mission launched in 1989, but it’s very much more than that. Gaia monitors each of its target stars about 70 times over a five-year period. It is expected to discover hundreds of thousands of new celestial objects, such as extra-solar planets and brown dwarfs, and observe hundreds of thousands of asteroids within our own Solar System. The mission is also expected to yield a wide variety of other benefits, including new tests of the  General Theory of Relativity.

Gaia will created an extraordinarily precise three-dimensional map of more than a thousand million stars throughout our Galaxy (The Milky Way) and beyond, mapping their motion, luminosity, temperature and chemical composition as well as any changes in such properties. This huge stellar census will provide the data needed to tackle an enormous range of important problems related to the origin, structure and evolutionary history of our Galaxy. Gaia will do all this by repeatedly measuring the positions of all objects down to an apparent magnitude of 20. A billion stars is about 1% of the entire stellar population of the Milky Way.

For the brighter objects, i.e. those brighter than magnitude 15, Gaia  measures their positions to an accuracy of 24 microarcseconds, comparable to measuring the diameter of a human hair at a distance of 1000 km. Distances of relatively nearby stars are measured to an accuracy of 0.001%. Even stars near the Galactic Centre, some 30,000 light-years away, have their distances measured to within an accuracy of 20%.

It’s an astonishing mission that will leave an unbelievably rich legacy not only for the astronomers working on the front-line operations of Gaia but for generations to come.

 

Lisa Pathfinder – better late than never!

Posted in Science Politics, The Universe and Stuff with tags , , , , , , , on December 3, 2015 by telescoper

Determined to post about something positive after yesterday’s act of collective idiocy by Parliament I find myself given a golden opportunity by today’s successful launch of the Lisa Pathfinder experiment by the European Space Agency.

As space missions go, LISA Pathfinder seems quite a modest one: it is basically a pair of identical 46 mm gold–platinum cubes separated by 38 cm. The idea is to put these test masses in free fall and measure their relative positions as accurately as possible.

After a false start yesterday, LISA Pathfinder was successfully launched in the early hours of this morning and is now en route to the First Lagrangian Point of the Earth-Sun system, about 1.5 million miles from Earth, at the location marked L1 in the diagram:

Lagrange_saddle

The contours show the “effective potential” of the Earth-Sun system, which takes into account the effect of rotation as well as gravity. The five Lagrangian points are the places at which tis effective potential is locally flat, i.e. where its spatial gradient vanishes. Any physics student will know that when the gradient of the potential is zero there is no force on a test particle. What this means is that an object placed exactly at any of the 5 Lagrangian points stays in the same position relative to the Earth and Sun as the system rotates. Put a spacecraft at one of these points, therefore, and it stays put when viewed in a frame rotating around the Sun  at the same speed as the Earth.

It’s not quite as simple as this because, as you will observe the Lagrangian points are not stable: L1, L2 and L3 are saddle-points; a  stable point would be a local minimum. However, around the first three there are stable orbits so in effect a test mass displaced from L1, say, oscillates around it without doing anything too drastic. L4 and L5 can be stable or unstable, in a general system but are stable for the case of the Solar System, hence the tendency of asteroids (the Trojans) to accumulate at these locations.

You may remember that WMAP, Planck and Herschel were all parked in orbits around L2. A spacecraft positioned exactly at L2 is permanently screened from the Sun by the Earth. That might be very useful if you want to do long-wavelength observations that require very cool detectors, but not if you want to use the Sun as a source of power. In any case, as I explained above, spacecraft are not generally located exactly at L2 but in orbit around it. Planck in fact had solar cells on the base of the satellite that provided power but also formed a shield as they always faced the Sun as the satellite rotated and moved in its orbit to map the sky. The choice of L1 for LISA Pathfinder was made on the basis of spacecraft design considerations as it will operate in a very different manner from Planck.

The reason for doing eLISA is to demonstrate the technological feasibility of a much more ambitious planned gravitational wave detector in space originally called LISA, but now called eLISA. The displacement of test masses caused by gravitational waves is tiny so in order for eLisa it is necessary (a) to screen out every effect other than gravity, e.g. electromagnetic interactions due to residual charges, to great precision and (b) to measure relative positions to great accuracy. That’s why it was decided to fly a cheaper technology demonstrator mission, to prove the idea is feasible.

LISA Pathfinder won’t make any science discoveries but hopefully it will pave the way towards eLISA.

It has to be said that LISA Pathfinder has had a fairly troubled history. I just had a quick look at some papers I have dating back to the time when I was Chair of PPARC Astronomy Advisory. Among them I found the categorical statement that

LISA Pathfinder will be launched in 2009.

Hmm. Not quite. It’s obviously running quite a long way behind schedule and no doubt considerably over its initial budget but it’s good to see it under way at last. There will be a lot of sighs of relief that LISA Pathfinder has finally made it into space! Now let’s see if it can do what it is supposed to do!

 

 

 

It’s Official, it’s PLATO!

Posted in Science Politics, The Universe and Stuff with tags , , , , on February 19, 2014 by telescoper

Just a quick post to pass on the news that the European Space Agency has officially selected the third M-Class mission to form part of its Cosmic Vision Programme (which covers the period 2015-2025). The lucky winner is PLATO (PLAnetary Transits and  Oscillations of stars) and it will detect extra-solar planets by monitoring relatively nearby stars, searching for tiny, regular dips in brightness as planets transit in front of them. It will also study astroseismological activity, enabling a precise characterisation of the host star of each planet discovered, including its mass, radius and age.

plato_satelliteIt is expected that PLATO will find and analyse thousands of  such exoplanetary systems in this way, with an emphasis on discovering and characterizing Earth-sized planets and super-Earths in the habitable zone of their parent star. PLATO will be launched on a Soyuz rocket from Europe’s Spaceport in Kourou by 2024 for an initial six-year mission. It will operate from the Second Lagrange Point, or L2 for short. It’s an intriguing design consisting of 34 small telescopes (left).

PLATO joins Solar Orbiter and Euclid, which were chosen in 2011 as ESA’s first two M-class missions. Solar Orbiter will be launched in 2017 to study the Sun and solar wind from a distance of less than 50 million km, while Euclid, to be launched in 2020, will focus on dark energy, dark matter and the structure of the Universe.

The decision to select PLATO wasn’t exactly a surprise as it was singled out as the leading candidate by an expert panel last month, but there was nevertheless some nervousness among certain senior astronomers at the Royal Astronomical Society on Friday in advance of the formal decision. I suspect they’ll all be out celebrating tonight!

Top Ten Gaia Facts

Posted in Astrohype, The Universe and Stuff with tags , , , on December 20, 2013 by telescoper
Gaia looks nothing like the Herschel Space Observatory shown here.

Gaia looks nothing like the Herschel Space Observatory shown here.

Since yesterday’s successful launch of the European Space Agency’s Gaia mission I have been inundated with requests for more information about this impressive satellite and the science behind it. As a service to the community, and for the edification of the public at large, I therefore thought I’d share my list of top ten Gaia facts via the medium of this blog:

  1. The correct pronunciation of GAIA is as in “gayer”. Please bear this in mind when reading any press articles about the mission.
  2. The GAIA spacecraft will orbit the Sun at the Second Lagrange Point, the only place in the Solar System where the  effects of cuts in the UK science budget can not be felt.
  3. The data processing challenges posed by GAIA are immense; the billions of astrometric measurements resulting from the mission will be analysed using the world’s biggest Excel Spreadsheet.
  4. To provide secure backup storage of the complete GAIA data set, the European Space Agency has commandeered the world’s entire stock of 3½ inch floppy disks.
  5. As well as measuring billions of star positions and velocities, GAIA is expected to discover thousands of new asteroids and the hiding place of Lord Lucan.
  6. GAIA can measure star positions to an accuracy of a few microarcseconds. That’s the angle subtended by a single pubic hair at a distance of 1000km.
  7. The precursor to GAIA was a satellite called Hipparcos, which is not how you spell Hipparchus.
  8. The BBC will be shortly be broadcasting a new 26-part TV series about GAIA. Entitled WOW! Gaia! That’s Soo Amaazing… it will be presented by Britain’s leading expert on astrometry, Professor Brian Cox.
  9. Er…
  10. That’s it.