Messenger in orbit

The Mercury Messenger probe is intended to make a long burn to decelerate into Mercury orbit tomorrow (Thursday 17th March). If successful this should be the start of a year of detailed observations of the innermost planet.

It's taken the spaceprobe six and a half years to get to the right place at the right time and at the right velocity to make a major 15 minute engine burn for capture into Mercurian orbit.

This is, frankly, an astonishing achievement. Hopefully all will go well and the prime mission will return very large amounts of new and detailed knowledge about the innermost planet.

Read more on these web pages...

• NASA's MESSENGER website
• MESSENGER - the spacecraft (Wikipedia)
• Mercury - the planet (Wikipedia)
• APL information on the orbit insertion burn

SCIENCE - 500 planets

Not that long ago (pre 1994) we only knew of nine planets, and one of those has been demoted to dwarf planet status. Today we know of nearly 500!

The reason for the huge increase is that astronomers are discovering planets around stars other than our own Sun using several techniques.

Sometimes this can be done by accurate measurements of the parent star's brightness. If a planet orbiting the star happens to pass in front of it, it will block part of the light and the dip can be measured and timed.

Another method involves tracking the position of a star very accurately. If it wobbles to and fro ever so slightly this is evidence of a smaller object in orbit around it - a planet or a faint companion star.

More recently it's become possible to image some of these planets directly by detecting the light they reflect from their parent star. This is pretty tricky, but just about doable using current telescopes. Of course we can't see any details, the planetary image is essentially a highly blurred point source. But it's still a very impressive feat of technology.

'Discover' magazine's website presents a gallery of these images, with good explanations in terms most people will understand. It's well worth a look.

The number of exoplanets will continue to rise and will soon pass the 500 mark. And one day, with better telescopes, it may even become possible to see some basic detail on some of these planets. But that is probably a long, long way off.

See also: Fomalhaut b

SCIENCE - The biggest collisions

We all know what happens when two objects collide, don't we? It depends on the speed of collision and the nature of the objects. Two balls of dough will stick together, billiard balls will bounce apart, slowly moving cars will stop one another, fast moving cars will crumple.

At some of the largest scales imaginable colliding galaxies pass through one another in a shape-distorting ballet that takes tens of millions of years. Where there were once two spiral galaxies, eventually there will be a single elliptical galaxy. To understand this process it becomes necessary to take into account the presence of dark matter in and around the two galaxies as well as the collisions of gas and the gravitational interactions of countless stars.

But what happens at an even larger scale? What happens when clusters of galaxies collide?

To understand this process more clearly, scientists at three prestigious labs in the USA have run a very large, very complex computer simulation. It took a long time to create and run the model, but you can watch the results in a movie that takes less than three and a half minutes.

What are you watching? First you will see the dark matter interactions, then the mixing of the intergalactic gas, and finally the combination. I should mention that what you see is a series of stop-start movies. In each one some interaction is shown, then the movement stops while the stationary scene is rotated to give you a better view and help you visualise the shapes, then the action moves on again.



For more information about the simulation and what you are seeing, visit Ian O'Neill's article on Discovery News.

The Antikythera Mechanism

The heavily corroded remains of an intricate and strange looking mechanism were found in 1901 in a Mediterranean shipwreck. Sixty years later after painstaking cleaning and study, it emerged that the device was a mechanical analogue computer for predicting the movements of the sun and moon in the sky. Various replicas have been built based on the known features of the mechanism.

The Antikythera mechanism makes it abundantly clear that the Greeks were advanced, not only in their scientific knowledge, but also in their mechanical technology. Reports from ancient writers like the Roman author, Cicero, describe mechanisms such as Antikythera. But until the corroded remains were recovered and studied these written accounts seemed fanciful. Surely the ancient world had nothing this advanced?

More recent studies have used high resolution X-ray tomography, and better reconstructions have become possible.

One of the later reconstructions can be seen working in the video below. If you view the video from You Tube you can switch to a higher resolution.



The X-ray tomography data has opened up a new window into the workings of the device. But it has also enabled historians to read a considerable amount of Greek text from the metal surfaces. This text consists partly of labels on the various scales and displays the mechanism used to present the positions of planets, calendar dates and so forth. The remainder of the text is a guide on how to use the device.

A great deal can be learned from the inscribed text. The names of the months varied from place to place in the ancient Greek world and this means we can determine its place of manufacture or intended use to be the central Mediterranean, not as originally supposed the eastern Aegean.

A longer and more technical video is presented on the Nature website (select the high resolution version and watch it in full-screen for the best view). There are also links to the Nature paper by Freeth, Jones, Steele, and Bitsakis, and a Nature news story (though there's a fee for the full text of these).

Wikipedia's article on the mechanism provides more detail for the average reader and has an excellent list of references, links, and suggested additional reading. One of the links is an article from New Scientist giving a good deal of background.

Links

• In search of lost time - Nature article, Nov 2006

Fomalhaut b

What, you may ask, is 'Fomalhaut b'? If you are interested in astronomy you will already know. Fomalhaut b is a planet circling one of our Sun's nearest neighbour stars.

Fomalhaut b has been imaged twice by the Hubble Space Telescope, once in 2004 and again in 2006. This is important because it's the first time a planet outside our own Solar System has been seen to have moved in its orbit around its central star.

This is extraordinary news indeed. It's the same scale of forward step as Galileo seeing craters on the Moon for the first time, or discovering the rings of Saturn, Halley predicting the return of his eponymous comet, or the Apollo 11 Moon landing in 1969.

Why is it so important? It's a milestone because astronomers have long assumed that other stars have planets. In recent years the presence of such planets has been indirectly detected, but this is the first time we can claim to have seen the light reflected by an exoplanet. You may not have realised it, but you have just lived through a truly historic moment.

The difficulty of making these images is difficult to grasp. Look at the picture again (you can click the image to see the full-size version).

The star - In the middle of the full image (but near the upper left in the article's thumbnail picture) is a small white circle. This is not part of the image, it was added later, but it marks the position of the star (Fomalhaut). In reality the star would be far smaller, just the tiniest speck, it's shown much larger to make it easy to see.

The obscuring disk - if the Hubble telescope had just been pointed at the star, the overpowering brightness would have flooded the image with light so that nothing but glare would be visible.

To see details really close to the star, it's essential to block the direct starlight. This was done by moving an obscuring disk in front of the star, and this is seen in the image as the irregular black area around the central white dot.

The halo of diffracted light - Outside the black zone, some starlight is still diffracted into the surrounding area. This is the circular zone that looks like the iris of an eye, close inspection of the large version of the image reveals that it's made up of lines of light radiating out from the position of the star. This not a real, distant object, it's created by subtle interactions between the starlight and the structure of the telecope.

The debris disk - The oval shape (clearly visible only in the full-size version) is a band of dust, gas, and orbiting rock and ice particles. It's part of a disk of material which is in the process of condensing into planets. Fomalhaut is a young star and is still developing a planetary system.

The planet - Just inside the inner edge of the dusty band is where astronomers thought there might be a planet, and sure enough when they looked they found one! This is a gas giant, probably much like Jupiter though something like twice as large, and it is so bright that many astronomers suspect it must have a ring similar to Saturn's (but larger).

The real clincher is that the planet appears in two Hubble photos of Fomalhaut, taken two years apart. It has moved, as expected, in its orbit around the star.

For more information see

• Wikipedia article - on Fomalhaut b
• BBC news article - about the discovery
• Astronomy Picture of the Day - the Keck Telescope's observations
• Gemini Observatory - details on exoplanet observations in infra-red light

Who moved our spacecraft?

Some spacecraft have trajectories that are slightly unexpected. Something has speeded them up or slowed them down - but what? Current methods of analysing and predicting spacecraft behaviour involve many factors, but the figures just don't add up. Something strange and unexpected is going on.

The major factors that affect spacecraft motion are gravity and rocket propulsion. Spacecraft and indeed all bodies in the solar system, from dust grains right up to the the largest planet Jupiter, move through a complex gravity field. Each body is tugged upon by every other, and the strength of pull depends on the masses involved. The mathematics is very complex and for more than two bodies involves iteration.

The second major factor comes into play whenever a manoevering engine is fired, this clearly changes the trajectory (which is the purpose of the engine of course).

The velocity of a spacecraft can be measured very accurately by examining its radio signals. Changes in velocity cause a change in frequency. But the calculated trajectories don't always match up with the measured ones.

There are many other subtle factors that affect a spacecraft. Pressure from solar radiation, loss of gas from the spacecraft's systems, impact by small particles, relativity effects, loss of speed due to passing through the outermost fringes of a planetary atmosphere, magnetic and electrostatic fields, and more.

But effects such as these are quite well known and can be allowed for. Yet the figures still don't quite add up. And nobody knows why.

The effect was first noticed decades ago as the Pioneer probes passed into the outer Solar System. They were travelling ever so slightly slower than they should have been. At the time this didn't cause much surprise, it was put down to some minor effect that nobody could identify and, like all these effects, it was far too small to affect the mission. Several possibilities were discussed at the time, none of them were accepted enthusiastically.

But it's happened again, and again, and again with other spacecraft.

At last a pattern is beginning to emerge. All the affected spacecraft have made close planetary passes to help shape their trajectory (gravity assists), while other spacecraft have not been affected. John D Anderson, Curator of Aerodynamics at the National Air and Space Museum in the USA, has been looking very carefully at the evidence. Anderson and others working with him have now come up with a mathematical formula which may enable them to predict the size and direction of the effect, it seems to work for all the effects seen in past spaceflights and they're waiting with bated breath to see if it accurately predicts the effect for Rosetta as it made its second fly-by of Earth last November (they haven't seen the data yet). There's another opportunity in November 2009. (John Anderson's scientific paper is "Anomolous orbital-energy changes observed during spaceflight fly-bys of Earth", John Anderson et al., Physical Review Letters, Vol 100, p 091102. There's also a report in New Scientist, 20th September 2008, pp 38-41).

All of this is quite fascinating, both to spacecraft engineers and to physicists; it really does seem as if something may be slightly wrong with our theory of gravity or there's some other effect at work that we are not yet aware of. Either way, prepare for a major new discovery in physics. But either way, don't hold your breath. Finding the underlying mechanism could take quite some time (years or decades, perhaps even longer).

Earth and Moon movie

NASA has done something amazing. One of their spacecraft has made a movie of the Moon passing in front of the Earth as it orbits our planet.

This was not a simple achievement! To see things from a suitable distance you need to have a camera position many times further away than the Moon.

A hundred and twenty times as far as the Moon would be fine, and this is what NASA has done.

Just think, the Moon circles the Earth once every 28 days, drawing out a circle half a million miles across. From our perspective the Moon glides past the starry constellations of the night sky.

But if we could travel far enough away we'd see the Moon sometimes one side of the Earth, sometimes the other, but never straying very far.

First, sit back and watch the movie. Then come back and read more of this blog post to find out how it was done.

In the year 1610 Galileo saw four points of light changing position night by night when he turned his telecope on the bright planet Jupiter. He realised that these points of light were circling Jupiter. It was final proof that not all celestial bodies orbit the Earth and therefore our planet cannot be the centre of the universe as was supposed by the mediaeval church.

This is exactly how the Moon would be seen to behave from a camera 31 million miles away, and this is what the video shows.

Here's how this amazing video was made. The Deep Impact spacecraft successfully investigated a comet in July 2005, but with its primary mission completed NASA decided it could usefully perform two further tasks. The Deep Impact team realised that they could also use the spacecraft to take images of the Earth and Moon, and they commanded the craft to take a series of images through four different colour filters at 15 minute intervals. Afterwards, the images were combined to make full colour versions and a series of the colour images were put together to make the video.

Learn more about Deep Impact (now renamed EPOXI) and the Earth/Moon video from NASA's website.

Astronomy

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Why am I interested in astronomy? I think it's because I'm fascinated by the vastness of the Universe and the amazing variety of objects it contains - including, of course, the Earth.

I don't remember when I developed this interest. I do remember being 14 or 15 years old and saving my pocket money to buy 'The Observer's Book of Astronomy' (I still have it), and around the same time I remember watching 'The Sky At Night', a monthly TV program that is one of the longest running series ever. It was (and still is) presented by Patrick Moore whose enthusiasm was intense and exciting. That was in the days when TV was only available in black and white.

I remember being even younger and looking at a nearly total eclipse of the Sun through heavily smoked glass, it was 30th June 1954, just a few weeks before my sixth birthday. Dad wanted me to see the eclipse because there wasn't going to be another like it in the UK until 1999!

What on earth?

This is an amazing image for a variety of reasons. What is it? Could it be a pulsating jellyfish from deep in the ocean? An iridescent soap bubble against a black background? Maybe it's a cell viewed in a fluorecence microscope?

No, the truth is stranger than any of these. Much of the 'light' you see here is invisible, the rest is far too faint to see. This bubble is the result of a sudden event witnessed by the Saxons, although it actually happened during the Stone Age. The photograph was taken by a range of telescopes, not all on the earth's surface.

This is SN 1006, a supernova remnant. Everything about it is awesome, almost beyond the human mind's ability to appreciate. And of course it's not on Earth at all. An astonishing feature of this little corner of the universe where we live, our Milky Way galaxy.

What is Supernova 1006? How did it happen? How was the image made?

Creation speaks of the Creator (KN)

Science, art, music, poetry, and every human endeavour can illuminate the truth about the Almighty, even when that was not the original intention.

I've been reading a book called 'The Bit and the Pendulum' by Tom Siegfried, science editor for the Dallas Morning News. He discusses the ways in which scientists are discovering that information lies at the heart of existence.

Here's a short extract...

Siegfried writes

'There are many hints from the frontiers of research that the information viewpoint will allow scientists to see truths about existence that were obscured from other angles. Such new truths may someday offer the explanation for existence that visionary scientists like [John Archibald] Wheeler have long sought.'