Eclipse of Europa by Io, today 5th May 18:16 AEST

[andyc (Andy)]

A quick heads-up for visual observers and imagers - in case you're not already aware (and there's not a thread elsewhere I've missed)... I read in Australian S&T that Io eclipses Europa this evening with both moons well away from the limb of Jupiter, well-placed for eastern Australia and New Zealand. And Sydney, at least, might well be clear for once!

All times from Australian S&T and in AEST (so add/subtract local time differences):
Umbral 1st contact 18:14:40
Mid-eclipse 18:16:12
Umbral last contact 18:17:40

Apparently the best event of its kind in this mutual event season, with a 1.3 mag dimming of Europa...

[deanm (Dean)]

Good call, Andy, but CdC shows me the event happening some hours earlier (15:50, Adelaide time - so well prior to 18:15 on the East coast...)

Daylight won't help, either.

Dean

[andyc (Andy)]

I managed to get an observation of this event - Europa became noticeably dimmer for a few minutes in the 16" scope. I took a series of photos through the event in my small scope, but they are fairly blurry and I'm not sure I'll make the effort of getting them ready for presentation. They do show a slight drop in magnitude (Europa dims a little, while Io and the others do not), but I only caught the end of the event on camera and it's pretty underwhelming image quality. But it qualifies as the first time I've seen a mutual satellite event!

Dean, it looks like Cartes du Ciel is incorrect. The event is listed in the tables here at the IMCCE (the premier group for observing these events it would appear) for 08:13-08:18 UTC, which was 18:13 to 18:18 Sydney time, 17:43-17:48 Adelaide time (start to end of penumbral phase). You can reach that page following instructions on this page, which has a lot of useful info and this IMCCE page has a link to description of the column headers. I had a situation earlier this year when I used Stellarium to try and observe an eclipse reappearance of Ganymede, and found I was looking at it 40 minutes too early... 40 minutes after Stellarium showed the reappearance, Ganymede popped out, which just happened to be the light-travel time from Jupiter to Earth! It sounds like CdC is out by more than that in this case, so there's a different issue, but I think it shows that some planetarium software isn't up to the task for these unusual events.

[deanm (Dean)]

Andy - if you imaged/observed the event, then clearly CdC & me are wrong!

I hope you can post some pics - these things aren't so common..?!

Cheers!

Dean

[andyc (Andy)]

Yeah, not common at all, especially under a clear sky! I'll see if I can post something, but it's almost embarrassingly poor quality...

[OzEclipse (Joe Cali)]

Dean, it looks like Cartes du Ciel is incorrect. The event is listed in the tables here at the IMCCE (the premier group for observing these events it would appear) for 08:13-08:18 UTC, which was 18:13 to 18:18 Sydney time, 17:43-17:48 Adelaide time (start to end of penumbral phase). You can reach that page following instructions on this page, which has a lot of useful info and this IMCCE page has a link to description of the column headers. I had a situation earlier this year when I used Stellarium to try and observe an eclipse reappearance of Ganymede, and found I was looking at it 40 minutes too early...

Some software uses geocentric rather than topocentric references for anything other than rise and set times. If the object is at the zenith, ie you are on the line between the object and Earth's centre, there is little or no difference. If you are north or south you may get a miss and if you are east/west, you'll get time and parallax offsets. Not sure about the products/web sites measured.

For occultations / NEO's and solar system bodies, the NASA Horizons
http://ssd.jpl.nasa.gov/horizons.cgi

and the Minor Planet & Comet Ephemeris Service
http://www.minorplanetcenter.net/iau/MPEph/MPEph.html

both provide consistent and accurate ephemerides particularly for near Earth bodies. The above sites produce ephemerides for single bodies. It isn't particularly useful for occultations. You would need to produce two sets of data for each body and compare position info to calculate an occultation.

[deanm (Dean)]

Thanks, Joe - well explained!
Dean

[kkara4 (Krishan)]

I was well prepared for this event and captured continuous IR longpass and IR,G,B runs over the 18:13 to 18:18 period.

Seeing was good to fair. Once processed I will post up images.

Times were based on WinJUPOS, which i find to be quite accurate.

I hope when I go through the images I actually captured the event.

Else epic fail

[DaveGee (Dave Gault)]

IMHO the one-stop-shop for occultation and eclipse prediction and analysis software is Dave Herald's 'Occult'.
http://occultations.org/observing/software/
it's free.

[andyc (Andy)]

Thanks for the info Joe - though for off-earth shadow events like eclipses of Jupiter's moons (or even of our own Moon), or the shadow of one Jovian moon falling on another, the timings are identical wherever you are on Earth, especially for the events beyond the orbit of the Moon. Geometry doesn't change the fact that the object's surface itself is being shaded. Geocentric vs topocentric coordinates don't affect these, though the light travel-time matters for events at Jupiter and beyond.

Occultations are a different matter - where you are on Earth affects the geometry of the occultation, exactly as you say.


Krishan, I hope you have a success, that would be great if you did!

Dave, that looks like a useful bit of software.

[kkara4 (Krishan)]

Originally Posted by andyc

Thanks for the info Joe - though for off-earth shadow events like eclipses of Jupiter's moons (or even of our own Moon), or the shadow of one Jovian moon falling on another, the timings are identical wherever you are on Earth, especially for the events beyond the orbit of the Moon. Geometry doesn't change the fact that the object's surface itself is being shaded. Geocentric vs topocentric coordinates don't affect these, though the light travel-time matters for events at Jupiter and beyond.

Occultations are a different matter - where you are on Earth affects the geometry of the occultation, exactly as you say.


Krishan, I hope you have a success, that would be great if you did!

Dave, that looks like a useful bit of software.

Hopefully Andy! I copied the videos to my processing computer last night, ready for processing tonight/tomorrow.

I completely forgot about the non-negligible light travel time from Jupiter. I had GPS coordinates and UT precisely entered and synchronised respectively about 30 minutes prior to the event, so provided WinJUPOS allows for light time, etc, I should have captured the event.

The seeing is another matter...

[Tropo-Bob (Bob)]

There is a replay of this event on Tuesday (12/5) involving the same Moons. The dimming is a little less at 0.9 mag. Happens from 20.29 to 20.34 EST. Twenty minutes after the event, there is an occultation of Callisto.

[ralph1]

I observed it, for a few minutes Europa appeared to dim relative to the other moons. Definitely worth watching again!

[kkara4 (Krishan)]

I have added my images of the event in the Solar System section. Was successful after all