Forum Replies Created
-
Posts
-
Alex – Thanks for pointing that out. My thanks to Helen Usher who worked with the VESPA team to help them link to our comet image archive. This will certainly make amateur images of comets more visible to the professionals.
Yes, Google Earth is probably best. The lat/long in Google Earth is WGS84 and its georeferencing is accurate at the few metres level over much of the UK (mainly the flat bits since projection on mountains is much harder). A few years ago I checked this for my telescope using a surveying SBAS/GNSS receiver which, ultimately, is cm level accurate in WGS84 if you leave it long enough. The position it got was around 1.5m from the position I read from GE and about 6m different in height although I couldn’t work out which geoid reference it was using.
For most astronomical purposes, apart from very precise astrometry of near objects and meteor triangulation, you don’t need that kind of accuracy. In any case, at the metre level you need to be very careful what system you use. Lat/Long is generally WGS84 but height depends on the exact reference geoid and, for instance, the GMN meteor camera network uses EGM96. I think the difference between those two can be 10s of metres (height) in some places.
James – As Alex says uncooled cameras like DSLRs or mirrorless cameras can do a very good job for generally less money than a cooled camera. Modern CMOS sensors are very low noise even at room temperature. Here is an image of the comet taken with a Sony A7s:
https://britastro.org/observations/observation.php?id=20241020_080600_25df8a3cd03b0737
I think a lot comes down to good processing rather than cooled or uncooled sensors.
I agree with Grant. You want to get your cal frames right before you go any further. This is really important for something faint and fuzzy like a comet. I tend to take 50 each of flats, flat darks and darks at the same temperature/gain/ISO. You need to make sure that the flats are taken at the same focus and aperture settings. I expose the flats to have a median of around half the saturation level. All of the cal frames are then averaged before you use them. The calibrated subs are then:
calibrated sub = (light – dark) / (flat – flatdark)
I tend to use sky flats but I do have a cheap artist’s tracing panel that I bought from Amazon which works well if I can’t get a sky flat.
One other thing. For Bayer colour sensors I tend to debayer the (flat-flatdark) to extract the green channel before then using it to divide the (light – dark). This is because I tend to use sky flats which are generally blue and which would therefore change the white balance. There are lots of ways to do this which ultimately work the same way but the key thing is to start with high quality cal frames by averaging lots of them.
In terms of what ISO to use with your camera have a look online at astro website for your particular camera. Assuming that you are using raw format there is an ISO which is generally optimises read noise and dynamic range. An example for the Mark 1 Sony A7s is here: http://www.astrophoto.fr/sony_a7s_measures.html.
Richard,
Apart from generating very pretty aurorae the increased solar activity has a significant effect on small satellites in low Earth orbit, not only in terms of the increased radiation environment but, more significantly, through increased drag which requires the use of propellant to maintain the desired orbital altitude.
Nick.
This event happened on the night that I had to leave at 2am to get to Heathrow for a flight to La Palma so I didn’t have much chance to see it. The all-seeing eyes of the cameras in my garden did record it though and I’ve just got around to looking at the video. This is a timelapse from 2000 – 0000 UTC from my NW camera in Chelmsford:
https://nickdjames.com/aurora/aurora_20241010_ndj.mp4
It was a remarkably bright and active display for us down here in the south.
That’s two really spectacular displays so far this year. The first one while I was away at the BAA meeting in Greenock and the second when all my cameras were picked for a trip to La Palma. Could someone please arrange that the next one occurs at a more convenient time…
Denis is correct that, generally, you need to submit your images to the Comet Section directly if you want them to be included in the archive but I’m happy to make a special case for BAA members for this comet while it is a bright object. I’ll collect suitable images from the Observations gallery and will send them to Denis for inclusion in the section archive as long as there is sufficient information (date/time/location/instrument/FoV) included in your submission to make this worthwhile.
Generally, though, please consider submitting your images to the Section through the route described by Denis above.
I’ll be producing a report for the December Journal.
Torrential rain this evening for me on La Palma so I have spent some time putting together this mosaic of the comet based on images from my ASI2600MC + RedCat 51 taken last night (Oct 14). Each panel is approx. 5×4 deg and the total image is 17.3 x 4.2 kpix:
https://nickdjames.com/Comets/2024/2023a3_20231014_ndj.jpg
If you zoom in you will find Comet 13P/Olbers about midway along the bottom of the image, also the globular M5 and quite a few galaxies. 13P looks very puny compared to C/2023 A3.
Thanks to everyone who managed to observe the comet last night. There are some great images here and in the gallery. It looks like there was a lucky break in the weather over NW Europe. The comet will now be moving into darker skies and the tail will be getting longer in the evening sky over the next few days so definitely worth making the effort.
I’m very envious. I’m on La Palma at the moment and it was raining at the top of the mountain yesterday evening. The forecast isn’t brilliant for tonight either!
So that does look very interesting. A normal spectroheliograph has an oscillating slit. Is my understanding correct that this relies on the Sun drifting across the slit to form an image? Looking at the tripod it is clearly not driven. If so, it must use some clever sensor integration trick.
Yes, the tail geometry changes very quickly over the next few days. The most recent animation from STEREO shows how quickly the tail is swinging around from its viewpoint.
This is the latest STEREO HI image from 2328 on October 7. The tail structure from the viewpoint of STEREO is now very complex.
Attachments:
And from October 6 at 2338 UTC. Lots of detail visible in that broad tail. STEREO-A is currently 26 deg ahead of us along the ecliptic so it is seeing the comet from a different point of view. Tomorrow (Oct 9) is the date of conjunction. The comet will then pull away from the Sun into the evening sky.
Attachments:
Here’s the latest uncompressed FITS from the STEREO HI. This is from Oct 5th at 23:28. Lots of nice tail detail visible.
Attachments:
60s exposure in grotty, hazy conditions from Chelmsford tonight (Oct 4) shows it around mag 13.2 unfiltered vs Gaia G.
Attachments:
It is continuing to fade. For photometry it is worth checking that you don’t include the 15th mag star just west. There are also a few 17th and 18th mag stars within a few arcsec that will come into play as it fades. Attached image taken earlier this evening as it got dark.
Attachments:
Last night (July 14/15) was clear here in Chelmsford. This asteroid is now 12 million km away and is around 19.3 at its brightest. It varied quite a bit over my 20x60s subs and, at its faintest is probably mag 20 or so.
https://britastro.org/observations/observation.php?id=20240715_211942_4a7a99b2a55cc815
