Notes and Links from the August Meeting

Chairman’s reports

This Saturday, 11th August the Perseid meteor shower will occur on a moonless night. However, the forecast at the moment is poor.

Astronomical News

  • Members may still join arrangements for a second visit to Alston Observatory is being organised for Tuesday 2nd October
  • The NASA Parker Solar Probe is due to be launched this Saturday 11th August. The probe will fly into the solar corona and will investigate the Solar wind and the heating of the solar corona to very high temperatures.
  • A pair of images of Neptune illustrated the gain in using new Adaptive Optics by the VLT. The images demonstrate that the VLT with the latest adaptive optics can be competitive with the Hubble Space Telescope. The new technology is also applicable to the future 40m-class telescopes (e.g. the E-ELT) and is essential to get the best out of these new assets.
  • The MeerKAT interferometric radio telescope in South Africa can now produce science images. An image of the centre of the Milky Way was shown, which reveals new detail of unexplained filaments in the region.

Orbital Physics and Spacecraft Manoeuvring

A member gave an Illustrated talk and demonstration to explain an orbit: throw hard enough until your ball goes over the horizon and continues to fall towards the planet at the same rate as the ground ‘falls away’ due to the curvature of the planet resulting in a circular orbit. The problem of manoeuvring without changing orbits was illustrated with the failed docking scheduled for Gemini 4 before their first spacewalk. From a distance, increasing speed by the trailing vehicle changes the vehicle’s trajectory into a higher and more elliptical orbit.

Olber’s Paradox

  Why is the night sky dark?   A member’s talk described the paradox attributed to  Heinrich Wilhelm Olbers ( 1758–1840).  Given an infinite number of stars that compensate intensity decrease with distance, the night sky should light. Although the Big Bang specifies that the material in the universe is finite, there are more than enough galaxies to cover one per a pixel on telescopes in the foreseeable future making the paradox still valid. The currently the solution accepted is that space is expanding: thus, cooling radiation and shifting radiation towards the red and radio. Other explanations are also mooted.

Explanatory solution addendum added by a member:

Infinite or not, the universe is of a size that means that even travelling as fast as they do, photons from some distant stars have yet to reach us. There will certainly be some redshift arising from the expansion of the universe, but this effect can be ignored by recasting the paradox in terms of radiation generally, rather than the much smaller visible spectrum. So irrespective of wavelength, the paradox is why there is not an infinite bath of radiation. The “fractal” explanation is a way round the homogeneous assumption inherent in the paradox, and as in the talk, the fractal calculations of the universe diverge from the required dimension. So I think we’re left with the “it hasn’t reached us yet” solution. And, of course, it never will reach us – but that’s a different talk.

Telescope Mount Alignment

The types of astronomical telescope mounts were explained by a member:  Altazimuth  and  Equatorial . Current ‘GoTo’ software offers the opportunity to iterate polar re-alignment. How accurately does the polar alignment need to be for time exposure photography? After much work and many calculations , our member discovered that the error reported by the software, for the polar misalignment, may be used as the drift across the image in 24 hours. Hence the rate of drift can be quickly calculated. The pixel coverage for a given camera together with the focal length of the system can be used to determine the sky coverage per pixel, eg 2 arc seconds/pixel. The rate of drift can then be used to determine the time to drift across one pixel (or maybe more) to find the maximum exposure time for the reported polar alignment error. In summary, tolerance for the error in polar alignment can be calculated beforehand. The telescope polar alignment procedure can then cease when within the desired tolerance.