Alex Pratt

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Viewing 20 posts - 1 through 20 (of 182 total)
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  • in reply to: New website feedback #610485
    Alex Pratt
    Participant
    in reply to: Star Count results #610481
    Alex Pratt
    Participant

    Hi Daryl,

    The light trends feature suggests that conditions have improved a little at some of my light-polluted locations and worsened at my rural sites. Hmmm. I leave it to others to investigate and comment on this.

    Alex.

    in reply to: Star Count results #610479
    Alex Pratt
    Participant

    Hi,

    To check the level of light pollution at a specific location in the British Isles (or overseas) I use

    https://www.lightpollutionmap.info/

    I find that its SQM readings and Bortle Scale estimates are in good agreement with my own obtained on my travels.

    Additionally, use

    https://lighttrends.lightpollutionmap.info/

    to click on a location and generate a plot of the trend in light level.

    Clear skies,

    Alex.

    in reply to: New website – members’ full names #610065
    Alex Pratt
    Participant

    After logging out/in a couple of times I was able to get a clean login to Edit my Web profile. I’ve now reset my displayed name to its previous shorter version.

    Alex.

    in reply to: Brookhaven on the market #609876
    Alex Pratt
    Participant

    I received a copy of Starlight Nights when I was a youngster. It was wonderful and inspiring to read about Leslie Peltier’s journey of astronomical discovery. The attached image shows my first copy (1967) and the modern indexed version (1999).

    A gem of a book!

    Alex.

    in reply to: Future Events #609020
    Alex Pratt
    Participant

    Thanks Callum,

    Clear skies,

    Alex.

    in reply to: Video observations #608571
    Alex Pratt
    Participant

    I can’t see an option to allow me to edit my previous message. I should have written “If one of my videos is larger than the 2MB limit I upload it to my YouTube channel using one of its supported formats…”.

    Alex.

    in reply to: Video observations #608568
    Alex Pratt
    Participant

    Hi Steve,

    If one of my GIFs is larger than the 2MB limit I upload it to my YouTube channel, then provide a link to it on my BAA Member’s Page. Other media hosting options are available.

    Cheers,

    Alex.

    in reply to: Following JWST through Orion to L2 #585229
    Alex Pratt
    Participant

    I once had a telescope almost as badly collimated as that…

    https://blogs.nasa.gov/webb/2022/02/11/photons-received-webb-sees-its-first-star-18-times/

    Seriously though, I agree it’s fascinating to read the Webb blog

    https://blogs.nasa.gov/webb/

    Such well-written and informative articles by the team, explaining an amazing technical achievement in an easy to understand manner.

    Alex.

    in reply to: Triton’s diameter from occultation timings #585200
    Alex Pratt
    Participant

    Hi Tim,

    We have a lot of experience in recording various types of occultations, and as you say we followed the guidelines for this event and promoted the campaign amongst BAA observers. Many obtained good light curves. Looking at the figures in the paper, their criterion for selecting light curves (for the atmospheric modelling) even rejected the data from the 1-metre at Pic du Midi, no less. They had 90 light curves, so they could be selective.

    Note: “…the first group of figures corresponds to light curves that had sufficient S/N to be used in Triton’s atmospheric fit, while the second group is for light curves with lower S/N that were not used in the fit. It should be noted, however, that the best synthetic models expected for those light curves (plotted in grey in Figs. C.6-C.9) are fully consistent with the observations, in the limit of the noise level.”

    They received lots of good data and I’m sure we’ll contribute even better light curves next time.

    Cheers,

    Alex.

    in reply to: Triton’s diameter from occultation timings #585198
    Alex Pratt
    Participant

    Hi Michael,

    In addition to this paper modelling Triton’s atmosphere

    Occult – Minor Planet occultation observations – Summary lists

    gives the diameter and astrometric position of Triton derived from chord timings submitted by observers.

    Cheers,

    Alex.

    in reply to: Triton’s diameter from occultation timings #585195
    Alex Pratt
    Participant

    Hi Michael,

    I’m sure the S/N of the light curves would have been good enough to give an astrometric position and shape profile of an asteroid / TNO, but in this paper they’re studying Triton’s atmosphere, so their modelling has more demanding criteria. They rejected data from a 50cm scope because of light contamination from Neptune.

    Bruno once explained – In the case of modelling the atmospheres of solar system bodies, lower quality data provides astrometry, defining the position and shape of the body (the chords across Triton), and higher quality data are used to model its atmospheric density, temperature gradient, winds, etc.

    For a future campaign we need an image scale providing good separation between planet and moon, a S/N of ~10 (although magnitude of target and duration of occultation limits our choices), and a 12-bit sensor (or better) to capture more detail in the light curve.

    It’s quite a challenge to get good data. The Lucky Star team were delighted to have 90 light curves from this pro-am campaign.

    Cheers,

    Alex.

    in reply to: Triton’s diameter from occultation timings #585193
    Alex Pratt
    Participant

    The preprint of the formal paper by Joana Marques Oliveira et al has been published on ArXiV

    https://arxiv.org/abs/2201.10450

    The analysis and paper were the subject of her PhD thesis under the supervision of Prof Bruno Sicardy (Observatoire de Paris). Here’s a video of Joana’s defence of her thesis

    Soutenance de thèse – Joana Marques Oliveira – YouTube

    A number of UK observers recorded the occultation and contributed to this work.

    Alex.

    Alex Pratt
    Participant

    Hi Nick,
    In this case the relative distances to the 3-sigma zones weren’t as large as some events. There’s uncertainties in the asteroid’s orbit (hopefully to be improved with Gaia DR3) and there were no Gaia flags against the star, although it had no RUWE value, which probably contributed to the shift.

    There’s a recent discussion of RUWE here:

    https://groups.io/g/IOTAoccultations/message/71022

    We’ll continue to have some significant path shifts until the final Data Releases from Gaia minimise the uncertainties in asteroid orbits and stellar positions.

    Alex.

    Alex Pratt
    Participant

    Many thanks to everyone who attempted an observation. Most were clouded out unfortunately, except that I was fortunate to record the occultation during a convenient gap in the fast-moving clouds. Simon Kidd (Cottered) observed a miss event. Jesus Delgado (Spain) recorded an occultation of 58s duration. I used the Occult program to obtain this profile of Medea.

    The ellipse is fitted to only two well-separated chords, so regard it as a simplified representation of Medea’s true shape. Simon’s line delimits the eastern edge of the shadow track and suggests he was close to obtaining a brief ‘blink’ occultation. The asteroid’s shadow path was ~55 km to the east of the predicted track.

    If only we’d had better weather to obtain more chords across Medea.

    Alex Pratt
    Participant

    Thanks Michael.

    Medea’s event is at an altitude of ~60 degrees from our latitudes, so even if there’s thin cloud a slightly longer exposure / integration setting can be used without compromising the value of timing of a chord across this slow mover.

    You’re getting some wide tracks across Ireland, such as Brita later this evening, although it’s to the north of you

    https://cloud.occultwatcher.net/event/385-1071-123422-649676-U042816

    Cheers,

    Alex.

    in reply to: Members’ Pages – Bortle scale – suggestion #585126
    Alex Pratt
    Participant

    Hi Paul, My interest was to see the range of sky conditions affecting the members, so a simple ‘Bortle 4’ tag suffices for me. Not everyone will have (access to) a SQM, so they can assess their site by using online references to the Bortle Scale and either use the partly subjective descriptions, e.g. “Bortle 4- NELM 6.1-6.5 and M33 is a difficult averted vision object, only visible when high in the sky” criteria or via their SQM reading, as you say. Clear – and dark – skies, Alex.

    Alex Pratt
    Participant

    Hi Denis,

    The track is generally well established, although the observed track is often displaced some km from the predicted track. There’s small uncertainties in the asteroid’s orbit and the star’s position is well defined. More event details and an interactive ground track map are available in Occult Watcher Cloud

    https://cloud.occultwatcher.net/event/385-212-63655-649640-U011811

    Click on the world map, drag and zoom in to Tarbat Ness. Click at your location on the map and you’ll see your event mid-time is 20:13:20 UT, although your site is quite distant from the predicted shadow track (blue lines) and 1-sigma band (red lines).

    It’s worthwhile observing because Tim mentioned the importance of probing the space around Medea. Some asteroids have satellite moons and have been discovered by occultation observations. I suggest recording for 5 minutes centred on the mid-time.

    Clear skies,

    Alex.

    in reply to: Following JWST through Orion to L2 #585103
    Alex Pratt
    Participant

    JWST first light…

    This tongue-in-cheek image has been doing the rounds

    Originally a bit of fun by ESA staff for an earlier mission

    https://twitter.com/esa/status/1479405861130977280/photo/1

    Alex.

    in reply to: Following JWST through Orion to L2 #585101
    Alex Pratt
    Participant

    Hi Phil,

    This posting on the MPML forum (Archive visible to all) confirm its changes in brightness

    JWST 095 Observations (groups.io)

    After observing other targets last night I had a look at JWST to get some video astrometry. By then thin cloud was coming and going. I haven’t reduce my data but at Jan 7.903472 it was near to mag 15, but a while later at 7.905556 it looked to be around mag 14.5.

    Cheers,

    Alex.

Viewing 20 posts - 1 through 20 (of 182 total)