10 January 2022 at 12:44 pm #575134
Most asteroidal occultations are brief events, less than 10 seconds’ duration, so it’s rare to have one last almost a minute. Medea’s 145 km-wide shadow track will sweep down England and Wales
(212) Medea / UCAC4 581-011811 event on 2022 Jan 21, 20:35 UT (asteroidoccultation.com)
It takes place around 20:15 UT on Jan 21, a Friday evening with the target star high up in Taurus just a few degrees north of the Hyades. The magnitude drop will be 0.9 m and at the moment Meda’s sky motion is almost zero, producing a maximum occultation duration of 58.6 s.
A number of the UK’s experienced occultation observers will be recording this event and it would be most useful to add more stations to the ‘net’. (On 2011 Jan 8 observers in Japan timed 23 chords across Medea, obtaining high-quality astrometry of its position and deriving its shape profile).
The target star is mag 12.4, which is faint for visual observers, but the event could be recorded using digital imaging cameras. Computer clocks should be synchronised with a reliable UTC time source, although small timing uncertainties are acceptable for such a lengthy occultation event. Avoid saturating the target star and use the shortest exposure setting that still gives a S/N ratio of 3 or more.
Tim Haymes reminds me that this event is highlighted on pages 54 and 55 of the 2022 BAA Handbook. We can help observers to analyse their recordings of the occultation.
Alex.12 January 2022 at 9:45 pm #585107Tim HaymesParticipant
Thanks Alex for the reminder. Im looking forward to monitoring this long event. I am in the shadow and it could be one of the longest durations. We will see. My PB is a 29 second event. There is also the slim possibility of detecting a moon. The more observers there are, the better we can probe the space around Medea.
Good luck.13 January 2022 at 1:04 am #585108Denis BuczynskiParticipant
Is the shadow track well established. I see that I will be outside the track at Tarbatness. Is it still worth while me observing this event?
Denis13 January 2022 at 4:18 pm #585109
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
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.
Alex.19 January 2022 at 11:59 pm #585137Tim HaymesParticipant
As the occultation time approaches i see observers planning to observe on Occult-Watcher. This is good and i hope every one gets to see this remarkable event. But what will the maximum duration actual be? To find out we need observers on or near the mid line of the prediction. So anyone in the following areas would be helpful:
Redcar, Tadcaster, Castleford, Sheffield, Burton upon Trent, Solihull, Cirencester, Chippenham, Warminster, Weymouth and anywhere in between.
Good luck to everyone….20 January 2022 at 8:26 pm #585142Michael O’ConnellParticipant
Wishing you all clear skies and the best of luck with this event.
Unfortunately I’m too far west for this one.
For anyone lucky enough to be under the shadow path and who hasn’t tried observing an asteroid occultation previously, it’s a great time to give it a try.
Michael.21 January 2022 at 12:06 pm #585144
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
Alex.23 January 2022 at 8:24 pm #585151
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.23 January 2022 at 8:42 pm #585154Nick JamesParticipant
It was cloudy here in Chelmsford but I was a long way to the east of the track in any case. The 55km eastward shift is almost at the prediction’s 3-sigma error so that seems quite significant.23 January 2022 at 10:05 pm #585155
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:
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.
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