Things that go ping in the night

…and even day.

Recent tweets relating to the International Year of Astronomy, 2009 and Newbury Astronomical Society twitter #meteorwatch have included some discussion of listen to radio echoes from meteors in the sky.

Meteors entering the Earth’s atmosphere start to heat and burn with the force of friction. This creates some level of ionisation of the gas it has traveled through and ionised gas is able to reflect radiowaves. This has been known for some time and professional observatories like EISCAT, the European Incoherent SCATter radar use it to study the strength and altitude of the ionosphere of the Earth. But amateurs can make use of it as well.

FM commercial radio broadcasts on channels between 88 and 108 MHz. This range is sliced up into 0.1 MHz channels and the odd ones assigned to radio stations. If you take your own radio and cycle through the available channels, you’ll be able to find areas where there is a broadcast and channels where there is none. Free channels are defined as channels that have no broadcast on them and are not next to a broadcasting channel (which can ‘bleed’ into nearby channels). Now these are free either because radio stations broadcasting on it aren’t powerful enough to transmit to where you are (or your equipment isn’t powerful enough to make anything of the signal) or because the radio station is over the horizon and therefore can’t make a line of sight connection.

Now come the meteors.

A trail of radiowave reflecting ionisation between you and a radio station located between 600-800km (ideally, but 300-1,500km will do) away from you – over the horizon but close enough to give a good signal – will allow a radio station you can’t hear to suddenly become audible. The signal will last as long as the ionisation trail – between a fraction of a second and minutes.

In order to get the best reception of these pings, find your clear channel, point to a known radio station over the horizon and keep your aerial perpendicular to the radiant of the meteor storm (the position the meteor tails point to). The signal should be boosted and ideally a good amplifier used and the best results are achieved at the lower end of the MHz range.

If you have better or different equipment, then there’s other wavelength ranges you can use. If you have no radio equipment, then you can listen to someone else’s at this website. At that website, a constant radio signal broadcast in order to study meteors is caught in reflection and broadcast.

The Jordan Astronomical Society describes its first attempts to beat interference and get some radio meteor action here.

Chris Lintott will be on the Trafalgar Square Fourth Plinth doing some radio meteor work on the 14th of August (just after the #meteorwatch), the exact time to be decided the night before.

Q&A with the crew of STS-128

The next crew of the space shuttle Discovery have been doing a question and answer session on their mission STS-128, during which they’ll pop up to the International Space Station to drop off and pick up a few things as well as doing three spacewalks to support construction of the ISS. They did this during their prelaunch run through, it was then posted to NASA’s Youtube Channel:

As well as the occasional bulletins here, you can find updates on STS-128 on its mission pages, via twitter (@Astro_Jose on Discovery, @Astro_Tim on the ISS and @NASA everywhere) and live events at NASA TV. Heavens Above will indicate if the ISS or any other satellites are to pass over your location (once you’ve told the website where that is).

Small but fast

via Astronomy Now.

A comparison of the speeds at which stars orbit the galactic centre of small distant galaxies has shown them to be rushing round at the same orbital velocity as those in modern large galaxies like our own.

Compact galaxies, which existed in the early Universe, are typically five times the density of galaxies of similar mass in the present universe. Galaxies such as 1255-0, the subject of this study, which lived when the Universe was 3 billion years old (compared with 13.7 billion years now) represent an earlier time in the evolution of the giants we have now. Understanding their dynamics is crucial to determining how they got from that point to today’s less dense affairs.

Pieter van Dokkum, professor of astronomy and physics at Yale University, and his team used the Hubble Space Telescope to determine the size of the galaxy, then the eight metre Gemini South telescope in Chile to perform spectroscopic studies of the velocities of stars within it. The Doppler shifts of the light from the stars as they whizzed round provided a measurement of their orbital velocity.