Nick James

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  • in reply to: Artemis #612168
    Nick James
    Participant

    Ted Molczan has provided a table of expected magnitudes for the spacecraft (Orion) and the SLS upper stage and spacecraft adaptor (the Interim Cryogenic Propulsion Stage) on seesat:

    http://satobs.org/seesat/Aug-2022/0236.html

    They indicate that Orion will be 13th mag on the night of launch fading to 17th mag at lunar distances with the ICPS around 1 mag fainter.

    The ICPS will be deflected from the spacecraft trajectory by a disposal burn shortly after trans-lunar injection (TLI). This will target a lunar flyby which will put the stage into a heliocentric orbit. The stage will probably do a propellant dump shortly after the disposal burn as part of its passivation procedure. Sadly we are not going to see that from here but it could be an interesting sight for people in the right place. Have a look at Chris Taylor’s description of the equivalent from the Apollo 8 S-IV-B upper stage:

    https://www.hanwellobservatory.org.uk/news/apollo-8-from-the-other-side-of-the-pond

    JPL Horizons has an ephemeris for Orion but not the ICPS. It is likely that an ICPS ephemeris will appear here:

    https://projectpluto.com/sat_eph.htm

    Good hunting. Please post any images you get on this website.

    • This reply was modified 2 years, 4 months ago by Nick James.
    • This reply was modified 2 years, 4 months ago by Nick James.
    in reply to: Artemis #612158
    Nick James
    Participant

    Yes, it’s going to be a challenge. The attached plots show the visibility from my observatory in Chelmsford to give some idea. These show the altitude of the Orion spacecraft, the Sun and the Moon at the date shown along the bottom. On the night of the launch Orion is around 12 deg up at nautical twilight and descending. I don’t know how bright it will be but at 20h on the day of launch it will only be 10 deg up from here and it is already 79000 km away. The ISS at this distance would be around 4th mag and Orion is a lot smaller than the ISS.

    By the time the circumstances get better it is far away and close to the Moon as you can see from the second plot.

    I would love to be proven wrong and would be very impressed if anyone gets this from the UK!

    in reply to: Artemis #612152
    Nick James
    Participant

    It doesn’t look good for us in the UK.

    Assuming that the launch goes ahead at the start of the 2 hour window (12:33 UTC on Monday Aug 29) the geometry for the UK is poor with the spacecraft below the horizon at night for the first week. It is above the horizon in a dark sky on Sept 5/6 when it is at declination -27 and due south around 2100 UTC but, by then, it will be a long way away and close to the Moon in the sky (not a surprise really) low in Sgr.

    It gets to high northern declinations on the way back but by then it is heading for solar conjunction.

    All in all I doubt if anyone will image it from here. A good opportunity to use a remote telescope I think.

    in reply to: V482 Cyg #612044
    Nick James
    Participant

    The seeing seemed quite stable here tonight so I thought I’d have a go tonight at doing a set of very short exposures of V482 Cyg and selecting the best ones to stack. This gives very high resolution and allows a clear separation between the variable and the 15th mag star to the NW. The variable has certainly brightened relative to that star since the image I posted on Aug 13. This image is only 3 arcmin square with a pixel resolution of 0.14 arcsec. Given that I’m not on a mountain this is probably as good as I can get.

    The FWHM is around 1.5 arcsec and the circles are apertures of 1.7 arcsec radius centred on the Gaia catalogue position. This is unfiltered so the variable is likely to be quite a bit brighter than V would give.

    in reply to: Antitwilight Sky #612019
    Nick James
    Participant

    Hi Gianni,

    Here’s an example from the top of a mountain showing its shadow at sunset. This was taken from the peak of La Palma.

    in reply to: V482 Cyg #611993
    Nick James
    Participant

    PSF photometry works well in crowded fields but the separation of these stars is only 2.9 arcsec so getting good enough focus and tracking to ensure that the PSF of each object is not too blended needs a bit of work with an amateur telescope from sea level in the UK. My image was at a scale of 0.28 arcsec/pix and had a star FWHM of 2.2 arcsec so the stars are reasonably well separated but that was on a night of good seeing. CMOS cameras allow selective stacking a lot of short exposures so a strategy similar to that used by planetary imagers is probably worth trying.

    I ran source extractor on this image and it showed that V482 Cyg was about 0.2 mag fainter than the companion so probably about 15.2 unfiltered at the moment. The star is likely to be very red though.

    in reply to: V482 Cyg #611983
    Nick James
    Participant

    This star has now faded to around mag 15. Gary prompted me to look at my images since my magnitude estimates of this star were too bright as it faded. One of the problems with automating everything is that I don’t often look at images or the data derived from them and there is a fairly bright star only 7 arcsec to the SW which was within my photometric aperture. The AAVSO VSX does warn about this. Looking in detail at my unbinned images tonight there is also a 15th mag star only 3 arcsec to the NW of the variable and this will generate significant errors at the current level. This is not mentioned anywhere and I haven’t seen it on other images since it is normally swamped by the bright variable. It is in Gaia EDR3 (a demonstration of how good the optics in that spacecraft are). It is worth considering if you are doing photometry of this star at the moment.

    in reply to: Outburst of faint periodic comet 285P/LINEAR #611949
    Nick James
    Participant

    This comet continues to fade and become more diffuse following its outburst on Aug 1. Thank you to all of you who have sent in observations. Please keep observing this object as it expands and fades.

    The remarkable weather in SE England means that I have managed to image it every night since the outburst was announced on August 6. My lightcurve and a rather jerky GIF showing the development is attached to this post. The comet has now faded to around 15.7. Still a long way to get back to its ephemeris magnitude of 19.5.

    in reply to: Problems accessing member areas of the website #611862
    Nick James
    Participant

    And I see that you are now a victim of the very formal, full name problem reported elsewhere!

    in reply to: Discussions #611239
    Nick James
    Participant

    I think David’s point is a good one. I much preferred the previous behaviour where, once you were logged in on a particular machine, you were logged in forever. I know that it is only a few extra clicks but it does mean that there is more of a barrier to replying and interacting with content than there used to be.

    in reply to: Redshift #610560
    Nick James
    Participant

    That’s true but I was thinking of something with a bit more mass and capability like a small interstellar space probe. Accelerating charged particles to a significant proportion of the speed of light is relatively easy. Accelerating a spacecraft, even a very small one, is a lot harder.

    in reply to: V482 Cyg #610491
    Nick James
    Participant

    I mentioned this star during the Sky Notes at the BAA meeting in London today. Here is an image taken when I got home. It is unfiltered so the star is still quite bright. I assume that, a bit like R CrB, it will be quite red when it fades.

    in reply to: Redshift #610429
    Nick James
    Participant

    That’s true when z is cosmological but the point I was trying to make is that you can have z > 1 without having to invoke the expansion of space or any non-flat geometries. The article implies that you can’t.

    in reply to: Fireball 23.40UT #610417
    Nick James
    Participant

    Headline on the front page of the site today from Jim Rowe (https://britastro.org/2022/12th-may-fireball). It looks as if this one might have dropped 100g or so of meteorites over a rather hilly bit of South Wales. An excellent piece of work by all of the camera networks in UKFAll.

    in reply to: Fireball 23.40UT #610295
    Nick James
    Participant

    I just caught the very beginning of the trail on my SW facing UK004F camera at Chelmsford. This is the streak on the right side of the attached image. The GMN trajectory solver has a trajectory from UK0002, UK000W, UK003N, UK004F and UK004X which you can see here (https://tammojan.github.io/meteormap/) if you select the latest_daily solutions. It was also picked up by 3 French and 2 British cameras of the Fripon network and their analysis is here: https://fireball.fripon.org/displaymultiple.php?id=17507.

    in reply to: PR Her #610129
    Nick James
    Participant

    Yes, nothing there that I can see.

    Nick James
    Participant

    Paul, yes that’s the one.

    Nick James
    Participant

    Cees Bassa responded to my video pointing to this tweet from Jonathan McDowell:

    https://twitter.com/planet4589/status/1520284820450025472

    It was the de-orbit burn for the Angara AM second stage launched from Plesetsk yesterday.

    • This reply was modified 2 years, 8 months ago by Nick James.
    in reply to: Brookhaven on the market #609878
    Nick James
    Participant

    It is one of my favourite books too. Lovely descriptions of a lost time. I bought a second hand hardback of the 1967 edition a while ago for around 50p.

    $550K for a big house and ten acres seems a steal but it’s not selling. I’ve just had a nose on Google Streetview. Looks very nice although there has been a lot of development around there since Peltier’s day.

    in reply to: Ron Arbour #609669
    Nick James
    Participant

    I was honoured to speak at Ron’s funeral on Monday. It was very well attended and many BAA friends were present. An obituary will appear in the Journal in due course but, for now, I attach my tribute.

    Attachments:
Viewing 20 posts - 201 through 220 (of 889 total)