Observation by Robin Leadbeater: "Small… Far away” - A...

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Robin Leadbeater


Robin Leadbeater


2020 Apr 15 - 22:55


2021 May 10 - 13:51



  • ALPY 200 spectrograph
  • ATIK 428 camera
  • Celestron C11 SCT 280mm aperture f5.5

11x600s NGC 6214 5x600s M101


Three Hills Observatory Wigton Cumbria UK

Target name

NGC 6214, M101


"Small… Far away” - An estimate of the Hubble Constant

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“Small… Far away” -  An estimate of the Hubble Constant

Fans of the TV programme “Father Ted” will likely be familiar with the reference to the illusion of relative size due to perspective  (external link to You Tube).  Inspired by Nick Hewitt’s webinar marking a century since the "Great Debate”  , I decided to use this, combined with spectra of a couple of galaxies with similar morphology and spectra but very different apparent sizes (M101 and NGC 6214), to make a rough “back of envelope” estimate of the constant in Hubble’s law, the rate at which distant objects are receding from each other due to cosmological expansion, depending on their distance.  Remarkably, the result was close to the currently accepted value. (Flatteringly so given the assumptions and approximations) We cannot really say much from a sample size of 1 but additional measurements of similar galaxies might  give an idea of the precision.

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