APOD: A Mercury Transit Sequence (2016 May 04)

Comments and questions about the APOD on the main view screen.
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APOD Robot
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APOD: A Mercury Transit Sequence (2016 May 04)

Post by APOD Robot » Wed May 04, 2016 4:05 am

Image A Mercury Transit Sequence

Explanation: This coming Monday, Mercury will cross the face of the Sun, as seen from Earth. Called a transit, the last time this happened was in 2006. Because the plane of Mercury's orbit is not exactly coincident with the plane of Earth's orbit, Mercury usually appears to pass over or under the Sun. The above time-lapse sequence, superimposed on a single frame, was taken from a balcony in Belgium shows the entire transit of 2003 May 7. The solar crossing lasted over five hours, so that the above 23 images were taken roughly 15 minutes apart. The north pole of the Sun, the Earth's orbit, and Mercury's orbit, although all different, all occur in directions slightly above the left of the image. Near the center and on the far right, sunspots are visible. After Monday, the next transit of Mercury will occur in 2019.

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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by bystander » Wed May 04, 2016 4:34 am

Last edited by bystander on Thu May 05, 2016 3:18 pm, edited 1 time in total.
Reason: added S&T link
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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by Ann » Wed May 04, 2016 10:38 am

Look Ma, an eclipse!

(And maybe it's an elephant...)

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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by heehaw » Wed May 04, 2016 3:44 pm

Washington Post had an article a few days ago knocking Astrology of Mercury: https://www.washingtonpost.com/news/cap ... -going-on/

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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by MarkBour » Wed May 04, 2016 3:52 pm

Okay, so you're 2000 light years away from Sol, and staring at it patiently with a bunch of CCDs. And this transit happens. It seems incredible that we could detect it. If we're talking about our Kepler spacecraft, I think Mercury occulting Sol might be too subtle to detect at that distance.

I'm guessing that the limits of observability with a given camera that can detect stellar variations depend on the luminescence of the star (as seen at the camera) and then the relative size of the planet and star. It seems it would not matter how large the planet's orbit was, since at that distance it won't affect the area of blockage during an occultation. (Admittedly, larger orbits produce fewer events per time.) Here on Earth, so close to Sol, the size of an inner planet's orbit will have a large affect on the size of the silhouette-disk we see. I assume we have never detected a planet that was at all transparent. If ever there was one, I guess that would have to be an additional factor in determining the thresholds.
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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by Chris Peterson » Wed May 04, 2016 4:26 pm

MarkBour wrote:I'm guessing that the limits of observability with a given camera that can detect stellar variations depend on the luminescence of the star (as seen at the camera) and then the relative size of the planet and star.
It's purely a question of signal to noise. Measurement noise with good instrumentation reduces to the square root of the signal. So you can detect an arbitrarily small reduction in intensity given that you collect enough signal. In other words, all you need is a telescope with sufficient aperture. However, this presumes your star is a steady source. No star is perfectly steady, and if the degree of native intensity fluctuation is too large,the only way to detect a transit would be by comparing data over a long enough period to have many orbits.
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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by BMAONE23 » Wed May 04, 2016 4:58 pm

Considering that Mercury covered such a small portion of the Sun's surface (smaller than many larger Sun Spots) it would more likely go undetected by any instrument incapable of discerning a small Exo-planet from a Star-spot. The only telltale sign would be from the Duration and repetition of the event as planets cross in hours in a continual orbit while spots cross and can form and decay over the course of days, many crossing only once. (at least for our local star.)

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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by Tekija » Wed May 04, 2016 5:56 pm

BMAONE23 wrote:Considering that Mercury covered such a small portion of the Sun's surface (smaller than many larger Sun Spots) it would more likely go undetected by any instrument incapable of discerning a small Exo-planet from a Star-spot. The only telltale sign would be from the Duration and repetition of the event as planets cross in hours in a continual orbit while spots cross and can form and decay over the course of days, many crossing only once. (at least for our local star.)
Reversing the stakes, what is the angular diameter of the Sun for an imaginary Mercurian observer?

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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by Joe Stieber » Wed May 04, 2016 7:28 pm

Tekija wrote:Reversing the stakes, what is the angular diameter of the Sun for an imaginary Mercurian observer?
For the upcoming transit on May 9th, the sun will have an apparent diameter (from earth) of 0.528 degrees. The earth will be 1.009 au from the Sun and Mercury will be 0.446 au from the sun. Therefore, from Mercury, the sun will be about 1.009/0.446 x 0.528 = 1.2 degrees apparent diameter (data from the U.S. Naval Observatory's MICA software).

Given that Mercury will present an apparent diameter (from earth) of 12.0 arc seconds during the transit, and the sun will be 1900.8 arc seconds apparent diameter, Mercury will cover just 0.004% of the apparent solar surface area. Correspondingly, 99.996% of the solar surface will remain visible. Ignoring limb darkening, sunspots, flares, etc., that means Mercury will cause a miniscule 0.000043 magnitude dimming in the sun's nominal magnitude -26.7 brilliance during transit. Calculation: (log 0.99996)/(log of the fifth root of 100); diameter data from USNO's MICA.

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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by Fred the Cat » Wed May 04, 2016 10:16 pm

I wish I had the skill for this but maybe a real astrophotographer can take on the challenge. (Besides that I'm working on Monday) Wouldn't it be a great image to catch our sun with both Mercury and the ISS in transit?

That way Sol can have both perforations and a zipper. :ssmile: Who knows maybe a plane will fly by too? :wink: You never know. Supposedly it worked for Venus. :clap:
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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by Boomer12k » Thu May 05, 2016 12:42 am

Nice image of it...

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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by alter-ego » Thu May 05, 2016 4:11 am

Fred the Cat wrote:I wish I had the skill for this but maybe a real astrophotographer can take on the challenge. (Besides that I'm working on Monday) Wouldn't it be a great image to catch our sun with both Mercury and the ISS in transit?

That way Sol can have both perforations and a zipper. :ssmile: Who knows maybe a plane will fly by too? :wink: You never know. Supposedly it worked for Venus. :clap:
Looks like that was done for the 2004 Venus transit:
http://www.esa.int/Our_Activities/Human ... m_Slovakia
And the Hubble was captured during the 2012 Venus transit:
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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by DavidLeodis » Thu May 05, 2016 5:45 pm

I have been unable to open the 'above time-lapse sequence' link with 2 browsers that I have. I wonder if anyone else has that problem or is it just related to my internet connection? :?

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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by geckzilla » Thu May 05, 2016 8:55 pm

It's completely gone, David.
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: A Mercury Transit Sequence (2016 May 04)

Post by DavidLeodis » Thu May 05, 2016 11:22 pm

geckzilla wrote:It's completely gone, David.
Thanks geckzilla :). It's reassuring to find that it is not a problem with my internet connection.