APOD: ISS and Mercury Too (2016 May 13)

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APOD: ISS and Mercury Too (2016 May 13)

Post by APOD Robot » Fri May 13, 2016 4:06 am

Image ISS and Mercury Too

Explanation: Transits of Mercury are relatively rare. Monday's leisurely 7.5 hour long event was only the 2nd of 14 Mercury transits in the 21st century. If you're willing to travel, transits of the International Space Station can be more frequent though, and much quicker. This sharp video frame composite was taken from a well-chosen location in Philadelphia, USA. It follows the space station, moving from upper right to lower left, as it crossed the Sun's disk in 0.6 seconds. Mercury too is included as the small, round, almost stationary silhouette just below center. In apparent size, the International Space Station looms larger from low Earth orbit, about 450 kilometers from Philadelphia. Mercury was about 84 million kilometers away. (Editor's note: The stunning video includes another double transit, Mercury and a Pilatus PC12 aircraft. Even quicker than the ISS to cross the Sun, the aircraft was about 1 kilometer away.)

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Re: APOD: ISS and Mercury Too (2016 May 13)

Post by Joe Stieber » Fri May 13, 2016 4:25 am

I was amazed when I saw this image, and the video, of the ISS transit during the Mercury transit, quite an uncommon combination. Then I was really amazed when I saw it was taken from Philadelphia, a short hop from my home in the New Jersey suburbs of Philly. So I checked Cal-Sky to see the path of visibility and I was mortified to find the centerline passed a mere 0.3 km from my house -- I could have seen it from my front yard!!! What a dope I was for not checking Cal-Sky beforehand. I've seen a number of ISS passes across the sun and the moon, but to see one with Mercury in transit at the same time would have been a rare treat. Oh well, at least I saw the Mercury transit after being skunked by bad weather the last three times, this time from a field 5 miles from my home, which was outside the 5.6 km wide path of ISS visibility.

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Re: APOD: ISS and Mercury Too (2016 May 13)

Post by Nitpicker » Fri May 13, 2016 5:07 am

I was also amazed when I first saw this one. Still amazed now. Mr Legault has a habit of amazing me. And I bet he put additional thought into his position, so as to avoid the possibility of the ISS lining up with Mercury and potentially obscuring it.

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Re: APOD: ISS and Mercury Too (2016 May 13)

Post by Boomer12k » Fri May 13, 2016 6:50 am

Oh, Cool.... but tell me this.... WHY does it look like a T.I.E. Fighter????? :shock:

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Re: APOD: ISS and Mercury Too (2016 May 13)

Post by Thierry Legault » Fri May 13, 2016 6:54 am

First of all, thanks to the APOD editors and for those nice comments above. It's been a lot a efforts in time, money and energy for me to take those pictures (including one week of vacancy and all travel expenses from France). As you can see, there are clouds passing in front of the Sun during the transit of the ISS, and 10 minutes later the sky was fully overcast! The arrival of clouds was forecast and the days before I hesitated between different options of place, including taking domestic flights to go to Québec, Minneapolis and Miami, considering that there were 3 ISS transit lines passing over North-American continent during the Mercury transit.

I already had questions about the propeller of the Pilatus that does not seem to rotate. A fellow astronomer had the good idea to take the frames of the video and register them on the plane, showing that the synchronization between the rotation of the propeller and the frame rate of the camera was only approximate: http://www.mfavret.fr/AstroPhoto/201605 ... egault.gif

:)

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Re: APOD: ISS and Mercury Too (2016 May 13)

Post by Thierry Legault » Fri May 13, 2016 6:58 am

Boomer12k wrote:Oh, Cool.... but tell me this.... WHY does it look like a T.I.E. Fighter????? :shock:

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it's not the first time I have that comment about the TIE fighter, but it's not the case when you look at the close-up: http://www.astrophoto.fr/mercury-transit-2016-crop.jpg

Moreover, Empire spokesman confirmed that there were no TIE fighter flight scheduled that day :)

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Re: APOD: ISS and Mercury Too (2016 May 13)

Post by Thierry Legault » Fri May 13, 2016 7:30 am

Nitpicker wrote:I was also amazed when I first saw this one. Still amazed now. Mr Legault has a habit of amazing me. And I bet he put additional thought into his position, so as to avoid the possibility of the ISS lining up with Mercury and potentially obscuring it.
Actually I used the Calsky calculation for the transit of the ISS over Mercury to have them as close as possible, and found the right place to set up, but I re-checked the calculation just before the ISS transit and noticed that the transit line had moved 200-300m East. Anyway, even the updated line was not exacty the right place too (Calsky calculations, based on orbital data, are very accurate but not perfect anyway!)
:)

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Re: APOD: ISS and Mercury Too (2016 May 13)

Post by Anonyfuss » Fri May 13, 2016 4:33 pm

APOD Robot wrote:the 2nd of 14 Mercury transits in the 21st century
Peter Varhegyi wrote:It was the second of 14 transits of the Solar System's innermost planet in the 21st century?
The 3rd was!(sic)
http://eclipse.gsfc.nasa.gov/transit/ca ... talog.html
As Peter pointed out yesterday, this was the third event this century - 1) 2003 May 7, 2) 2006 Nov 8, 3) 2016 May 9, yes?

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Re: APOD: ISS and Mercury Too (2016 May 13)

Post by neufer » Fri May 13, 2016 5:47 pm

Anonyfuss wrote:
Peter Varhegyi wrote:
APOD Robot wrote:
the 2nd of 14 Mercury transits in the 21st century
It was the second of 14 transits of the Solar System's innermost planet in the 21st century?
The 3rd was!(sic) http://eclipse.gsfc.nasa.gov/transit/ca ... talog.html
As Peter pointed out yesterday, this was the third event this century
- 1) 2003 May 7, 2) 2006 Nov 8, 3) 2016 May 9, yes?
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Re: APOD: ISS and Mercury Too (2016 May 13)

Post by alter-ego » Sat May 14, 2016 5:39 am

Thierry Legault wrote:
Nitpicker wrote:I was also amazed when I first saw this one. Still amazed now. Mr Legault has a habit of amazing me. And I bet he put additional thought into his position, so as to avoid the possibility of the ISS lining up with Mercury and potentially obscuring it.
Actually I used the Calsky calculation for the transit of the ISS over Mercury to have them as close as possible, and found the right place to set up, but I re-checked the calculation just before the ISS transit and noticed that the transit line had moved 200-300m East. Anyway, even the updated line was not exacty the right place too (Calsky calculations, based on orbital data, are very accurate but not perfect anyway!)
:)
Unfortunately, TLE predictions (which Calsky uses) are not accurate enough for reliable, precision conjunction assessments like a satellite / planet overlap, and ground track accuracy typically is better nearer, or even prior, to the TLE epoch. In addition, a large, LEO satellite like the ISS adds further difficulty to the calculation due to unmodeled forces or maneuver corrections. Ultimately, confident conjunction predictions require other orbit propagator calculations that are more real time than the TLE propagator. So in your case of an angular "miss" of 0.1°, I estimate the correct ground position for a bulls-eye conjunction with Mercury to be ≈1.5km westeast of your location. Though I don't know the statistics, ground position errors of 100's of meters are probably fairly common.

Anyway, enough of this technical stuff.
You did a magnificent job with the ISS transit image and video - resolution and quality are outstanding, and imagery of the ISS and shuttle on your website are truly remarkable. I applaud your commitment to good (and honest!) work.
I'm sure we'll see an APOD from you again sometime.
A pessimist is nothing more than an experienced optimist

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Re: APOD: ISS and Mercury Too (2016 May 13)

Post by Thierry Legault » Sat May 14, 2016 11:11 am

alter-ego wrote:Unfortunately, TLE predictions (which Calsky uses) are not accurate enough for reliable, precision conjunction assessments like a satellite / planet overlap, and ground track accuracy typically is better nearer, or even prior, to the TLE epoch. In addition, a large, LEO satellite like the ISS adds further difficulty to the calculation due to unmodeled forces or maneuver corrections. Ultimately, confident conjunction predictions require other orbit propagator calculations that are more real time than the TLE propagator. So in your case of an angular "miss" of 0.1°, I estimate the correct ground position for a bulls-eye conjunction with Mercury to be ≈1.5km westeast of your location. Though I don't know the statistics, ground position errors of 100's of meters are probably fairly common.

Anyway, enough of this technical stuff.
You did a magnificent job with the ISS transit image and video - resolution and quality are outstanding, and imagery of the ISS and shuttle on your website are truly remarkable. I applaud your commitment to good (and honest!) work.
I'm sure we'll see an APOD from you again sometime.
thank you for those explanations and nice comments :)

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Re: APOD: ISS and Mercury Too (2016 May 13)

Post by Fred the Cat » Mon May 16, 2016 6:50 pm

Ok so we see Mercury's shadow but could we see "a" Mercury too? If it's expected a telescope might spot planets by blocking out a sun's light is there any chance we could really do it?

By the way – Thanks for the time and trouble Thierry. You nailed it again and APOD was nice enough to show it. :clap:
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