Forum Replies Created
-
Posts
-
Robin. Thanks for that. A very interesting paper.
The Sony IMX455 is certainly a very nice sensor for astronomy. Here’s what you can do with it if you couple it to a Celestron RASA 11 and have very dark skies:
https://www.spaceobs.com/Blog-de-Alain-Maury/MAP-historique-et-description
Nick.
Robin – That was a very interesting programme. Some of the BBC’s science output is still pretty good. Here’s my lightcurve so far taken from the BAA database. Hopefully this good weather will continue so we can keep monitoring it.
Attachments:
It’s now (2023-05-21 22h UT) around 11.3 so still brightening quickly. The total integrated magnitude of M101 is around 8.0 so this one object is currently 5% of the brightness of the entire galaxy.
That’s interesting. The latest non-detection on TNS is from ATLAS at 2023-05-18 10:17 UT when they reported > 20.5.
I imaged it earlier this evening (May 20/21) and it has risen to around mag 12.0 now.
Attachments:
It’s rather hazy in Chelmsford but here but here is an unfiltered image of the SN.
Attachments:
Yes, it is surprisingly bright. I assume that it is because of the very large solar arrays and a good solar aspect angle. The RIME antenna is now deployed too after a bit of a struggle with the mechanism.
Yes, I was a bit disappointed on my last visit to the NHM although I did get to see Winchcombe which made up for the impression that there were fewer meteorites on display there than when I was a lad. While in Western Australia recently I visited the WA museum in Perth. They had a lot of meteorites there including a big chunk of the 22t Mundrabilla meteorite sitting in the weather outside by the bike racks. It would have taken some shifting if anyone had wanted to steal it.
There is a confirmed report on MPML that JUICE flared up to around mag 18 last night (May 9) despite the distance being around 5.6 million km. I don’t know how long this will last but it would be worth a try tonight if you have a chance. It is currently at a declination of -4 deg and an hour or so past the meridian. It is currently cloudy in Chelmsford.
The spacecraft still has not successfully deployed the big RIME subsurface radar antenna. The latest news (not much really) is here: https://twitter.com/esaoperations/status/1655933988991795203.
I was monitoring it in Chelmsford using an HD11 + ASI6200. Half the telescope aperture was occulted by my observatory shed and the the rest was looking through the branches of a tree. Because of this I had to use 0.25s exposure to get the star. At least the sky was clear but but no occultation detected here.
The comet is currently in a faint state. The attached is a 60s exposure taken at 2127 showing the comet and the star.
Attachments:
Grant – You really do seem to have an extraordinarily unreliable system. If it was me I would have taken a sledgehammer to it by now.
Nick – Well done getting it. It was reported as mag 13 on the first night so in line with my original predictions. You might want to have a go for the Ariane upper stage too. You can get ephems from https://projectpluto.com/sat_eph.htm.
Grant – Good luck with imaging JUICE tonight. A typically excellent Ariane 5 launch. Acquisition of Signal at the ESA Deep Space Antenna at New Norcia was a bit of a nail-biter but in the end everything was fine. It just took a while for JUICE to settle itself down and enable its transmitter.
Attachments:
Mark,
Thanks for writing that up. It is good to see different approaches.
You are using an elliptical aperture which I don’t think is correct and probably explains the slightly brighter magnitude that you are getting since you will have included some of the dust tail. Comphot always uses a circular aperture which is reasonable since the comet’s coma is likely to be spherical and the rules are that you should not include the tail in the estimate. Also, how do you exclude stars that appear in the aperture? The sigma-clipped comet stack does significantly attenuate stars but they are not completely removed.
You make the comment that you would not normally use this approach with ASTAP. How would you normally deal with the fact that the comet is moving relative to the background since stacking over long periods is often necessary to get sufficient SNR in the outer coma?
Nick.
PS for Grant – Surely your home-brew camera software can query the mount’s commanded pointing position from SkyX and then insert the required FITS keywords. Blind solving is great but it is relatively slow so it is always best to have this data in the header. In particular Astrometrica is a bit of a pain to use if this is not there.
I wonder if the general public actually find these comparisons useful or is it just that journalists like to use them? Have we really reached the state where people can’t visualise something that is 10 m (or let’s say 40 ft) across? By all means use units that people are familiar with but I do wonder whether these comparisons are useful or even meaningful. I once saw the speed of the space shuttle in orbit described as 22 times the speed of sound. Discuss.
Mark,
Your 5.6 is a little brighter than comphot’s estimate which was 5.8 but that is not a bad agreement for a big comet. The full output from comphot is:
10×10 20×20 30×30 40×40 50×50 60×60
10.07 9.00 8.41 8.06 7.79 7.58 # Counts
10.07 9.02 8.48 8.11 7.84 7.62 # Median annuli
Total integrated magnitude: 5.78 (radius 891.1 arcsec)
COMPHOT: 1.4.6 2023 01 23.052 5.78 29.70 18.47 23.50 19.02 3076.2 5.50 Astrometrica 4.12.0.448 Nick James C_2022_E3__ZTF_ G_2022_E3_o_0000.fitThese measures are pretty much in the middle of the estimates on COBS:
Could you provide a step-by-step description of the approach that you used with ASTAP please?
Richard – Thanks for having a go at this challenge. Comphot estimates a coma diameter of 29.6 arcmin from these images. The attached file is one of the diagnostic plots that it produces and this one shows the diameter that it has determined. The estimator basically generates a set of circular rings centred on the photocentre and keeps going out until the level in the ring falls to less than 0.8*sigma above the median sky level where sigma is the standard deviation of the noise in the background image. This threshold is rather arbitrary but it seems to work reasonably well.
BTW this green frame is one of the components of the final image here:
https://britastro.org/observations/observation.php?id=20230123_023135_df98af0b86eb5907
The colour image nicely separates the green coma from the whitish dust tail.
Attachments:
The initial orbit of 2023 DZ2 was quite uncertain and the close approach distance was uncertain too. At one point the probability of impact at the next close approach (2026-03-27) was 1 in 670. This got the media interested. By March 17 the most likely miss distance this time around was 180,000 km. This gradually got revised and some old observations were found dating back to January so by March 20 we knew that the minimum geocentric distance was going to be near 175,000 km.
Far from being a possible impact in 2026 the miss distance will actually be around a million km. This shows how chaotic gravitational perturbations are for close approaches where a small inbound trajectory error can lead to a much larger outbound one.
