Category Archives: Glossary

Official names of stars and planets

If you’ve ever wondered what the conventions are for naming new stars, planets and other astronomical objects, then the IAU has a guide to most things here, except for stars, which have obviously found their way into many catalogs before the 1922 inception of the International Astronomical Union in Rome, so a note on star names (specifically why there’s no point ‘buying’ one) is here.


A couple of particle related bits

Neutrinos cause a lot of problems. These ‘ghostly’ particles have a habit of only interacting very weakly with ordinary matter, making their detection rather difficult. They are produced in massive numbers by fusion reactions inside the Sun, potentially giving us detailed information on what’s going on, but when we measure the type (or ‘flavour’) of neutrinos coming from the Sun, the ratios of each flavour don’t add up to what we’d expect (although the overall numbers are fine now we can add up the numbers of each flavour). A lot of head scratching later and the idea of neutrino oscillations came about. This focuses on wave-particle duality which essentially means every particle in the universe has some level of wave-like actions and some particle like characteristics. So photons of light hitting metals don’t impart their energy continuously like waves breaking on the shore, they give one pulse of energy, then another (meaning electrons requiring a certain amount of energy to leave the metal won’t do so until photons over a certain energy come at them). It also means particles like electrons can undergo wave like interactions like diffraction and interference. It was also suggested that neutrinos – particles – could interfere with one another in a wavelike way such that a group of different flavours would appear to contain a different ratio of flavours to the actual amount that were present when the beam came together. This is neutrino oscillation.

The oscillations required something that hadn’t at the time been measured – the neutrinos needed to have mass. An experiment was soon performed that didn’t show the masses of the neutrinos, but instead showed that the flavours – electron, tau and muon (plus their anti particles, named after the particles whose creation spawned them) – all had differences in their mass. If there were differences, then at least some of them had to have mass, which was enough to allow oscillations to occur. But some doubts still persisted as the oscillations themselves had never been seen – until now.

At the OPERA facility in Italy, they measure the numbers of muon neutrinos spawned by decays in the LHC in CERN, 730km away. They have an idea how many are being produced and where they’re headed over there and how many should be arriving where they are. They also know how many in theory are going to change from being muons to tau neutrinos. Now they have announced that a tau has been produced in a pure muon stream, the first tentative step to showing that oscillation happens – though a few more detections would be nice just to show there’s a trend here.

Meanwhile, in other astroparticle news, the IceCube detector has been looking not at muon neutrinos, but at muons themselves. Muons are a class of particle called Leptons that includes electrons and tauon particles, their anti-particles and their neutrinos. They are the heaviest of the leptons and so the least likely to pop into existence. They are created in high energy interactions and can be accelerated to high energies. The creation and acceleration of such exotic particles by magnetic fields and shockwaves associated with supernovae and stellar remnants such as neutron stars. But there’s been little evidence that this is so. There are limits to the energies of cosmic rays (hugh energy particles born outside of Earth) coming in from outside the solar system. On the low energy scale, the magnetic fields of the Earth and the solar wind deflect those charged particles that aren’t travelling our way with enough momentum. At the highest energies, charged particles are slowed by brehmstrallung radiation that opposes acceleration. Travelling through the cosmos, particles from various sources encounter the magnetic fields of interstellar space and are slowly massaged into a fairly constant background. But some relatively close structures can still be seen lurking in images of the sky taken using particles rather than light.

The map of incoming muons produced by IceCube, which is a nascent neutrino observatory, has shown there to be a slight excess of cosmic rays from the direction of the Vela supernova remnant. This remnant is 800 light years from us and 10,000 years old. Between it and us there is a second supernova remnant, often missed as it shines less brightly across most wavelength ranges (but still more brightly in gamma rays). Vela was the place where an observed neutron star was linked to a supernova remnant directly for the first time, could it now be the place that the first tentative observational proof of cosmic ray acceleration in such a system has been achieved?

…and sticking with muons for a moment. Fermilab recently released data on muon production at its particle accelerator facility. The data showed that production of muons outstripped production of anti-muons in proton-anti-proton collisions by about 1%. This is an important discovery, if confirmed, which could show the reason why the local universe is dominated by matter, rather than having equal amounts of matter and anti-matter. It has been hypothesised that this imbalance exists between the amount of matter and anti-matter generated in particle interactions, with subsequent annihilation between the particles leaving the excess of matter behind to form the things we see.

A demonstration of proper motion

Over the course of the night, stars will be seen to travel from East to West. Stop the Earth from rotating (or simply put a motor on your telescope to follow the rotation) and the stars seem to stop. Over the course of a year, however, the journey of the Earth around the Sun will lead to the stars wiggling about their position, with closer ones wiggling more than farther ones. This is the parallax effect, which can be seen simply by looking out of the window of a moving car and seeing things by the road moving across your field of view faster than things on the horizon. But remove all the terrestrial motions by taking two images at the same time of the year, but separated by several years and you may find some of the stars still move between frames. This is proper motion.

Proper motion is the actual motion of those stars compared to the position of our own Sun reflected in their apparent motions in the sky. Due to the distances involved, they are always very small, with the largest, the nearby Barnard’s star (a 9th magnitude red dwarf six light years from our Sun, the 4th closest star to it), moving 10.3 arcseconds (10.3/3600 degrees of arc, or about 190th of a Lunar angular diameter) per year. In two centuries or more that star will likely cross the sky by a distance similar to that of the angular diameter of the full Moon.

At this webpage, two photos are compared. One taken by the website owner on the 17th of March 2010 and one taken by the Palomar Observatory Sky Survey (POSS1) on the 20th March 1950. The Palomar plate shows not only the superiority of that telescope and viewing site, but also a number of field stars present on the website owner’s image. Over the course of sixty years, most of the field stars, and certainly the galaxies, have remained where they are, but a few close bright ones have shifted noticeably. The website includes a ‘blink comparator’ – an image that flashes between the new and old photos of the region.

Those nice fixed constellations up there? They’re on the move.

Sun watch from anywhere, whatever the weather

NASA has a Spaceweather media viewer available online. It brings together views of the Sun, the properties of the solar wind and the aurora in one area. It adds to them ‘illustrations’ (diagrams of topics of relevance), videos of people explaining these topics and ‘visualisations’, kind of animated diagrams of particular processes and effects.

Zoom is a bit buggy with my mouse – the middle button controls both zoom and scroll, which can be annoying – but asides from that, a nice little resource, helpful for the up coming Sun-Earth day on the 20th of March and likely to become even more interesting as the present solar cycle progresses.

Fancy a career in astronomy?

The International Astronomical Union has published a quick page on the career path of an astronomer. What you need, what you will do and everything beyond the looking through a telescope bit. Not that modern astronomers are allowed near telescopes, more computer screens to monitor what the technicians are doing to the multi million pound facility performing your requested observations…

What’s in your light cone?

In General Relativity, there is famously a cosmic speed limit of c, the speed of light in a vacuum. Nothing we are familiar with can exceed this limit, imposing a limit on the speed of causality – information about change travels at the speed of light. With this in mind, a website has been created to map the objects within a person’s ‘light cone’. A light cone represents the distance from an object light could travel with time. Simply put, you type in your birthdate and it will display objects light could have travelled to from the Sun in the time you have been on this planet. Click here to find what lies within your own past light cone.

Seeing further with Gravitational lenses

Gravitational lenses are part and parcel of the General Theory of relativity. In it, large masses such as stars and planets warp the fabric of space time like heavy balls sitting on a stretched rubber sheet (but transposed into three dimensions rather than two). The objects create indentations around them, which deepen with increasing object mass.

Eddington took part in a trip to the island of Principe in 1919 to witness an eclipse of the Sun in front of the brightest star cluster in the sky, the Hyades. When the bright solar light was blocked out, he saw in photographs that he took that the apparent positions of stars close to the Sun had been shifted away from its position. The closer they were supposed to be, the greater the shift. The shift was in line with the predictions of Einstein’s new theory (as opposed to Newton’s theory with the assumption of photon mass, which would give half the shift, or Newton’s theory with no photon mass, which would give no shift).

Since Eddington’s time, gravitational lensing has become an active observational and theoretical field. New results from teams in America and Germany have identified ways of using gravitational lensing (this time using galaxies passing in front of other galaxies, as is now much more common than using stars passing behind stars) to determine the age of the universe and Hubble’s constant, which defines the rate of the expansion of the Universe.

The new technique uses the fact that an off-axis (ie not perfectly aligned) galaxy lensed by another will be seen as multiple images around the lensing galaxy. These images involve light travelling different optical lengths (distances, with modifications for how difficult it is for light to travel over parts of them). This allows a single lensing event to provide multiple cases of the lensing effect that can then be used with general lensing theory to test it. A bit like solving multiple equations to get hold of certain constants.

It’s not all hard maths and philosophy though, sometimes the lead authors like Philip Marshall can relax with a glass of wine and a candle. It is after all one way to help describe to people how gravitational lensing produces the images it does…