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No, it’s not constant! More correctly it should be called the Hubble parameter and it evolves with time but the odd thin is that we have two discordant measurements at the current epoch.
These are two very accurate measurements made in two different ways that don’t agree at a significant statistical level. Planck gives 67.7 km/s/Mpc from observations of the Cosmic Microwave Background and Gaia/HST gives 73.5 km/s/Mpc from more direct observations of Supernova redshifts. The two are very different measurements. I think the Planck measurement assumes a particular cosmological model and fits a power spectrum to the variations in the CMB and then infers H from that. The Gaia/HST measurements use a conventional redshift v distance approach but, with Gaia’s parallax measurements and HST’s Cepheid measurements, we now have a much better distance ladder to the distant SNe.
All interesting stuff. Cosmologists and astronomers will never be out of a job.
One standard London bus is 0.05517776187067525650202815557146 furlongs long to within the accuracy of my calculator so this must be true.
OK Steve, you are going to have to explain how you measured the speed of light using a microwave oven and some chocolate. I’m guessing it is a rather circular argument involving standing waves and melted chocolate. What would Michelson and Morley make of it?
Here’s an image of it from last night. I get it to be 10.68 (using Gaia G and the green plane of this colour image)
Indeed. The speed of light is defined to be exactly 299,792,458 m/s but how much more fun it is to quote it in obscure units. I think it is around 1803 giga-furlongs/fortnight. At least a furlong is well defined (1/8 mile or approx 201m). The problem with NTUs is that they are so vague. How tall is a giraffe and what is the volume of a swimming pool? In most cases I don’t really think they help to visualise the object being described.
Owen, I guess the level of inconvenience depends on where you start from! The venue is a few minutes walk from the mainline railway station which is around 2.5 hours from either London or Edinburgh and tickets aren’t that expensive if booked well in advance. As others have pointed out there are several Park and Ride sites around York that would work for a day visit. York is a great city to visit too so you could make a weekend of it although best to stay some way outside the centre on a bus route if budget is limited.
Indeed. If there is an ISO standard giraffe then there aren’t many of them roaming the streets of Chelmsford for reference. At least I have a vague idea of how long a double decker bus is. I’m hoping that the journo that wrote this did it tongue in cheek but it is very difficult to tell…
Len. Good point. There are some good pubs within a few minutes walk. This being Yorkshire I’d have thought that you would be keen to save money by taking your own sandwiches into the pub and sneakily eating them whilst downing a (relatively inexpensive) beer. Perhaps York is too posh for that?
James, I think train bookings are possible three months in advance so they should be available for May 18 from next weekend.
Sorry you can’t make it. I hope to make videos of the talks but we had technical gremlins last time which meant that several of the talks weren’t recorded. Hopefully we’ll have a better run at it this time.
Automation of detection of transients is one of the things that even pros struggled with for a long time but they seem to have got it pretty well sorted now. I remember back in the late 90s helping Tom Boles with this and the main problem was that you had to accept a pretty high false alarm rate in order to avoid missing stuff. At that time it was just more efficient to blink manually.
I’ve got a large C library of image processing functions written over the years. One of them takes two images at the same scale, cross correlates them in the frequency domain to get alignment, attempts to blur the sharper one to get the same median PSF as the other one, normalises and then subtracts. I have to say that it is not brilliantly effective and that in the end I decided that I had more interesting things to do!
The human eye/brain combination takes some beating.
Robin, Impressive spectra given how faint this is. The sky is still getting dark here but the nova is considerably brighter than the 28th. I get 16.7 R tonight compared to 18.0 R two days ago.
There are at least four variable objects blinking on and off when I compare my median-subtracted frame from last night with one from early December. See if you can find them all here.
Tom – I was imaging the Moon during the eclipse, at this point with 5s exposures every 30s but I missed the impact at 04:41:38 by 8s. The timestamps in the attached half-scale images are the start of exposure (note the filenames are when the file was generated which is a few seconds after the shutter closed) and should be accurate to 0.1s or so. If there was another event at 04:42:01 I would have missed that by around 1s.
Clear in Chelmsford at the moment. Live images from my telescope appearing here.
That’s a fun observation. Perhaps it is a test for a subsequent Trump-centred edition where large parts of the world are erased.
I have to admit I let my S&T subscription lapse a few years ago. At the risk of sounding like a very old fogey it used to be a really good magazine that stood way above all of the others but now I think it is just one of many and I seldom found stuff of interest in it that I couldn’t get elsewhere.
