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robin_astro

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About robin_astro

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  1. An interesting question which has been pondered by cosmologist for many years. This Physics Stack Exchange question for example, although quite old covers most of the ground https://physics.stackexchange.com/questions/1048/what-if-the-universe-is-rotating-as-a-whole In summary It is possible to envisage an infinite, homogeneous, expanding, rotating universe. It would not be isotropic though and any observer could detect an axis of rotation, though the axis would be different for each observer. No anisotropy has been detected to date however (eg in the CMB) so the rotation must be small if present at all. Robin
  2. Hi Dave, Not sure if it was in the VSS or main meeting as I didn't go to Winchester in 2017 but I did see a couple of presentations by Stan at earlier BAAVSS meetings. Very impressive stuff ! Robin EDIT: there is another presentation at the Eccles meeting in 2011 which I did see http://www.britastro.org/vss/eccles11.htm
  3. Stan Waterman's survey work is a good example of the sort of dedication needed to actually find a new exoplanet. (over 100k images to date tracking several hundred thousand stars since 2000, predating the similar Kepler mission by several years. No exoplanets found as far as I know but loads of new interesting variables. http://www.stanwaterman.co.uk/variablestars/ https://www.britastro.org/vss/Stan Waterman Winchester 2017.pdf Robin
  4. Yes a t value of 5.9 (with 217 degrees of freedom) is very high so this means that for all intents and purposes, the measured brightness was definitely lower during the transit period. ie it is statistically highly improbable that a difference in mean this large could have happened by chance. Cheers Robin
  5. Hi Dave, If you need a t test calculator there are a few on line which will do it for you eg this one which has a nice expanation of the results https://www.mathportal.org/calculators/statistics-calculator/t-test-calculator.php You just cut and paste the values for the two sets of data into the boxes. A 1 tailed test is what you want to test if there was a statistically significant drop. (the 2 tailed test just tests if the means are significantly different) Just leave the other settings as the default Cheers Robin
  6. Hi Dave, The detection looks significant by eye but the software most likely just calculates the uncertainty based on the counts (ie that due to the random nature of photons arriving. That is only one of many possible contributions to the total uncertainty though and there will be other systematic variability which will add to the uncertainty. Since you have many repeat points though you can make a true measure of the uncertainty by taking the measurements during (say 23:00-01:00) and outside the transit and doing a t test on the two populations to determine if your observation that there was a dip is statistically significant. https://en.wikipedia.org/wiki/Student's_t-test Cheers Robin
  7. robin_astro

    Velocity Dispersion

    The velocity dispersion is usually defined as the standard deviation (sigma) of the radial velocities of the components in a rotating system. The orbital velocity can then be estimated from the standard deviation (v ~ sqrt3 sigma) and hence various parameters of the system (eg mass and radius) can be estimated https://en.wikipedia.org/wiki/Velocity_dispersion https://en.wikipedia.org/wiki/Virial_theorem#Galaxies_and_cosmology_(virial_mass_and_radius) Robin
  8. robin_astro

    New Supernova SN2018AOZ at mag 13.4

    In an average year there are about 9 supernovae that reach brighter than mag 14. Last year was high (14) but 2016 was low (5) 6 so far this year (From rochester astronomy bright supernova archives http://www.rochesterastronomy.org/snimages/archives.html ) Robin
  9. robin_astro

    HELP WITH VISUAL SPEC

    Hi Peter, You cannot just "nudge" the spectra,there must be something wrong with the wavelength calibration which you need to sort out. You are going round in circles. I recommend sticking with one program (and staying with one forum. I see your same questions on 3 or 4 different forums) Follow the tutorials I gave you on the BAA forum last year and again today. https://britastro.org/comment/3815#comment-3815 https://www.britastro.org/comment/4560#comment-4560 If you get stuck at a particular point, ask there with the exact details of what went wrong and I will try to help Robin
  10. robin_astro

    10 thousand million

    Small change. In the UK we spend 4.6 billion pounds a year just on our pets ! https://www.statista.com/statistics/308266/consumer-spending-on-pets-and-related-products-in-the-united-kingdom-uk/
  11. Cosmic Rays in this context is a "catch all" phrase for artifacts caused by various sources of radiation. (From showers of Muons produced in the upper atmosphere by cosmic rays, Compton scattering from background Gamma radiation and even beta radiation from the glass used in lenses, cover glasses etc. I believe this latter source caused big problems in the early days of CCD as some high dispersion glasses are very radioactive ! High energy photons (X rays, gamma rays) are not reflected off conventional mirrors, you need special "mirrors" with very shallow angle reflections to focus these Robin
  12. robin_astro

    Supermassive Black Holes

    Material (gas and dust) orbiting close to a galaxy central black hole can produce large amounts of energy through friction (heat). We see these as active galaxies and quasars, which are some of the most powerful objects in the universe. Even here though, the amount of material actually being consumed by the black hole is still very small compared with the mass of the galaxy and the radiation from these objects varies significantly when there is more or less material close enough. (There is not enough material close enough to our blackhole currently to produce the amount of radiation seen from a Quasar, though Sgr A is a strong source of radio emission) Robin
  13. robin_astro

    Supermassive Black Holes

    There are stars more than 13 billion years old in the Milky way so we know that galaxies are not consumed by their central black holes. This implies the rate at which stars fall into black holes must be extremely slow. (There is no surprise here, Mercury has been orbiting close to the Sun for billions of years without being consumed) When stars occasionally do fall into black holes, they release large amounts of energy, producing a so called tidal disruption event (TDE) which releases a lot of energy, similar to a supernova explosion. These are thought to be very rare per typical galaxy, perhaps 1 per hundred thousand years. See here for example https://www.gaia.ac.uk/alerts/what-and-why/why-are-we-looking/tde-agn An event like this in our galaxy would be obvious. You can see the stars near to Sag A orbiting our black hole here for example Robin
  14. robin_astro

    Speed Of Stars.

    You already have an estimate of the recession velocity for the galaxy. (The average radial velocity calculated from the redshifts of the two stars) You can then use Hubble's law to estimate the distance. This is only an estimate though as it assumes the recessional velocity is only due to cosmological expansion. In practise galaxies also move due to local gravitation effects and this can give significant errors in distances to nearby galaxies calculated this way (for example the Andromeda galaxy is actually moving towards us!) Robin
  15. robin_astro

    Speed Of Stars.

    Strictly speaking this is not the speed of the star it is the radial velocity (The component of the speed in the direction of the observer) Interestingly measurement of galaxy rotation is within the capability of amateurs eg as here by Christian Buil and Valerie Desnoux Robin
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