Explanation: On November 11, 2019 the Sun was mostly quiet, experiencing a minimum in its 11 year cycle of activity. In fact, the only spot visible was actually planet Mercury, making a leisurely 5 1/2 hour transit in front of the calm solar disk. About 1/200th the apparent diameter of the Sun, the silhouette of the solar system's inner most planet is near center in this sharp, full Sun snapshot. Taken with a hydrogen alpha filter and safe solar telescope, the image also captures prominences around the solar limb, the glowing plasma trapped in arcing magnetic fields. Of course, only inner planets Mercury and Venus can transit the Sun to appear in silhouette when viewed from planet Earth. Following its transit in 2016, this was Mercury's 4th of 14 transits across the solar disk in the 21st century. The next transit of Mercury will be on November 13, 2032.
<<Savinien de Cyrano de Bergerac (March 1619 – 28 July 1655) was a French novelist, playwright, epistolarian and duelist. Cyrano de Bergerac's works L'Autre Monde: ou les États et Empires de la Lune ("Comical History of the States and Empires of the Moon", published posthumously, 1657) and Les États et Empires du Soleil (The States and Empires of the Sun, 1662) are classics of early modern science fiction. In the former, Cyrano travels to the Moon using rockets powered by firecrackers (it may be the earliest description of a space flight by use of a vessel that has rockets attached) and meets the inhabitants. The Moon-men have four legs, firearms that shoot game and cook it, and talking earrings used to educate children.>>
Can somebody explain why there will only be 14 transits in the 21st century. Seems to me that every time Mercury goes around the sun that it would be visible against the sun as a backdrop. I cannot envision the geometry that would limit that to only 14 in 100 years.
Re: APOD: Mercury and the Quiet Sun (2019 Nov 14)
Posted: Thu Nov 14, 2019 4:31 pm
by Chris Peterson
BillLee wrote: ↑Thu Nov 14, 2019 3:23 pm
Can somebody explain why there will only be 14 transits in the 21st century. Seems to me that every time Mercury goes around the sun that it would be visible against the sun as a backdrop. I cannot envision the geometry that would limit that to only 14 in 100 years.
Mercury's orbit doesn't lie on the same plane as Earth's orbit. Most of the times that Mercury lies between the Earth and the Sun it is tilted enough above or below Earth's orbital plane that it isn't passing in front of the Sun's disc. It's the same reason we don't have a solar eclipse and a lunar eclipse every month (because the Moon's orbit around Earth isn't coplanar with Earth's around the Sun).
BillLee wrote: ↑Thu Nov 14, 2019 3:23 pm
Can somebody explain why there will only be 14 transits in the 21st century. Seems to me that every time Mercury goes around the sun that it would be visible against the sun as a backdrop. I cannot envision the geometry that would limit that to only 14 in 100 years.
Mercury's orbit doesn't lie on the same plane as Earth's orbit. Most of the times that Mercury lies between the Earth and the Sun it is tilted enough above or below Earth's orbital plane that it isn't passing in front of the Sun's disc. It's the same reason we don't have a solar eclipse and a lunar eclipse every month (because the Moon's orbit around Earth isn't coplanar with Earth's around the Sun).
BillLee wrote: ↑Thu Nov 14, 2019 3:23 pm
Can somebody explain why there will only be 14 transits in the 21st century. Seems to me that every time Mercury goes around the sun that it would be visible against the sun as a backdrop. I cannot envision the geometry that would limit that to only 14 in 100 years.
Mercury's orbit doesn't lie on the same plane as Earth's orbit. Most of the times that Mercury lies between the Earth and the Sun it is tilted enough above or below Earth's orbital plane that it isn't passing in front of the Sun's disc. It's the same reason we don't have a solar eclipse and a lunar eclipse every month (because the Moon's orbit around Earth isn't coplanar with Earth's around the Sun).
Bill - Thanks for asking. Was just going to do that myself. (Meant to yesterday when that info was up)
Chris - Thanks for the explanation
neufer - Thanks for the graphic.
Mercury's orbit doesn't lie on the same plane as Earth's orbit. Most of the times that Mercury lies between the Earth and the Sun it is tilted enough above or below Earth's orbital plane that it isn't passing in front of the Sun's disc. It's the same reason we don't have a solar eclipse and a lunar eclipse every month (because the Moon's orbit around Earth isn't coplanar with Earth's around the Sun).
Bill - Thanks for asking. Was just going to do that myself. (Meant to yesterday when that info was up)
Chris - Thanks for the explanation
neufer - Thanks for the graphic.
All who wish to understand space must learn to think in 3D, even though our displays, pictures in books, etc. are in 2D.
All who wish to understand space-time must learn to think in 4D.
Bruce
Re: APOD: Mercury and the Quiet Sun (2019 Nov 14)
Posted: Thu Nov 14, 2019 6:00 pm
by BDanielMayfield
The quietness of the Sun has been found to be rare among stars, and an exact solar analog is yet to be found.
Bruce
Re: APOD: Mercury and the Quiet Sun (2019 Nov 14)
Posted: Thu Nov 14, 2019 6:24 pm
by MarkBour
BDanielMayfield wrote: ↑Thu Nov 14, 2019 6:00 pm
The quietness of the Sun has been found to be rare among stars, and an exact solar analog is yet to be found.
Bruce
Today's image nicely shows the difficulty of an exoplanet search for smaller planets via a method such as the Kepler mission transit detection. If Mercury is 1/200th the diameter of the Sun, then it's area would block 1/40,000th of the Sun's disk, resulting in a temporary 0.0025% drop in the light observed. Or, 25 parts per million.
In the context of a distant star, that amount would be extremely difficult to detect above background-level fluctuations in the star's output and in our reception of that output. Wikipedia mentioned that Kepler found the median for the natural variability of the stars in its field to be about 19.5 parts per million. It's not so bad for an Earth-sized planet against the disk of a Sol-sized star, but it still took the integration of many orbits to get most of these detections. If Kepler had had more time before its reaction wheels went bad, it probably would have found many more Earth-sized exoplanets. https://en.wikipedia.org/wiki/Kepler_space_telescope (see Photometric Performance).
The article implies that it was a disappointment to the designers of the Kepler mission to find out that the stars fluctuated as much as they did. I think this observation (19.5 ppm) was about twice as much as they had hoped. They had based the initial estimate of only 10 ppm on observations of our Sun. As Bruce said, the Sun appears to be a very calm star.
Re: APOD: Mercury and the Quiet Sun (2019 Nov 14)
Posted: Thu Nov 14, 2019 7:23 pm
by neufer
MarkBour wrote: ↑Thu Nov 14, 2019 6:24 pm
If Mercury is 1/200th the diameter of the Sun, then it's area would block 1/40,000th of the Sun's disk,
resulting in a temporary 0.0025% drop in the light observed. Or, 25 parts per million.
Mercury is ~1/285th the diameter of the Sun resulting in a temporary drop in light of ~12.34 parts per million.
MarkBour wrote: ↑Thu Nov 14, 2019 6:24 pm If Mercury is 1/200th the diameter of the Sun, then it's area would block 1/40,000th of the Sun's disk,
resulting in a temporary 0.0025% drop in the light observed. Or, 25 parts per million.
Mercury is ~1/285th the diameter of the Sun resulting in a temporary drop in light of ~12.34 parts per million.
BDanielMayfield wrote: ↑Thu Nov 14, 2019 6:00 pm
The quietness of the Sun has been found to be rare among stars, and an exact solar analog is yet to be found.
Bruce
Capture.JPG
Today's image nicely shows the difficulty of an exoplanet search for smaller planets via a method such as the Kepler mission transit detection. If Mercury is 1/200th the diameter of the Sun, then it's area would block 1/40,000th of the Sun's disk, resulting in a temporary 0.0025% drop in the light observed. Or, 25 parts per million.
In the context of a distant star, that amount would be extremely difficult to detect above background-level fluctuations in the star's output and in our reception of that output. Wikipedia mentioned that Kepler found the median for the natural variability of the stars in its field to be about 19.5 parts per million. It's not so bad for an Earth-sized planet against the disk of a Sol-sized star, but it still took the integration of many orbits to get most of these detections. If Kepler had had more time before its reaction wheels went bad, it probably would have found many more Earth-sized exoplanets. https://en.wikipedia.org/wiki/Kepler_space_telescope (see Photometric Performance).
The article implies that it was a disappointment to the designers of the Kepler mission to find out that the stars fluctuated as much as they did. I think this observation (19.5 ppm) was about twice as much as they had hoped. They had based the initial estimate of only 10 ppm on observations of our Sun. As Bruce said, the Sun appears to be a very calm star.
Yes, it was the space telescope Kepler that first proved just how jittery the output of the average star is. Nice comment Mark.
MarkBour wrote: ↑Thu Nov 14, 2019 6:24 pm If Mercury is 1/200th the diameter of the Sun, then it's area would block 1/40,000th of the Sun's disk,
resulting in a temporary 0.0025% drop in the light observed. Or, 25 parts per million.
Mercury is ~1/285th the diameter of the Sun resulting in a temporary drop in light of ~12.34 parts per million.
MarkBour wrote: ↑Thu Nov 14, 2019 6:24 pm
If Mercury is 1/200th the diameter of the Sun, then it's area would block 1/40,000th of the Sun's disk,
resulting in a temporary 0.0025% drop in the light observed. Or, 25 parts per million.
Mercury is ~1/285th the diameter of the Sun resulting in a temporary drop in light of ~12.34 parts per million.
According to the U.S. Naval Observatory’s MICA 2.2.2 software, for the transit of 11-November-2019, the sun was 16’ 9.4” semi-diameter while Mercury was 5.0” semi-diameter. Therefore, the radius ratio of Mercury to the sun is: 5.0/((16 x 60) + 9.4) = 1/193.88. Since light loss is proportional to the area obscured (ignoring any limb effects), Mercury would have blocked (1/193.88)^2 or 1/37,589 of the solar area. That’s 0.0027% or 27 ppm of the solar light.
MarkBour wrote: ↑Thu Nov 14, 2019 6:24 pm
If Mercury is 1/200th the diameter of the Sun, then it's area would block 1/40,000th of the Sun's disk,
resulting in a temporary 0.0025% drop in the light observed. Or, 25 parts per million.
In the context of a distant star, that amount would be extremely difficult to detect above background-level fluctuations in the star's output and in our reception of that output. Wikipedia mentioned that Kepler found the median for the natural variability of the stars in its field to be about 19.5 parts per million.
Mercury is ~1/285th the diameter of the Sun resulting in a temporary drop in light of ~12.34 parts per million.
According to the U.S. Naval Observatory’s MICA 2.2.2 software, for the transit of 11-November-2019, the sun was 16’ 9.4” semi-diameter while Mercury was 5.0” semi-diameter. Therefore, the radius ratio of Mercury to the sun is: 5.0/((16 x 60) + 9.4) = 1/193.88. Since light loss is proportional to the area obscured (ignoring any limb effects), Mercury would have blocked (1/193.88)^2 or 1/37,589 of the solar area. That’s 0.0027% or 27 ppm of the solar light.
In the context of a distant star Mercury is ~1/285th the diameter of the Sun resulting in a temporary drop in light of ~12.34 parts per million. That amount would be extremely difficult to detect above background-level fluctuations in the star's output of about 19.5 parts per million.
Mercury is ~1/285th the diameter of the Sun resulting in a temporary drop in light of ~12.34 parts per million.
According to the U.S. Naval Observatory’s MICA 2.2.2 software, for the transit of 11-November-2019, the sun was 16’ 9.4” semi-diameter while Mercury was 5.0” semi-diameter. Therefore, the radius ratio of Mercury to the sun is: 5.0/((16 x 60) + 9.4) = 1/193.88. Since light loss is proportional to the area obscured (ignoring any limb effects), Mercury would have blocked (1/193.88)^2 or 1/37,589 of the solar area. That’s 0.0027% or 27 ppm of the solar light.
In the context of a distant star Mercury is ~1/285th the diameter of the Sun resulting in a temporary drop in light of ~12.34 parts per million. That amount would be extremely difficult to detect above background-level fluctuations in the star's output of about 19.5 parts per million.
Thanks for the clarification! I tend to drift off at the discussion of exoplanets.
Re: APOD: Mercury and the Quiet Sun (2019 Nov 14)
Posted: Thu Nov 14, 2019 11:36 pm
by neufer
Joe Stieber wrote: ↑Thu Nov 14, 2019 11:25 pm
I tend to drift off at the discussion of exoplanets.
“These are not the planetoids you are looking for”
Re: APOD: Mercury and the Quiet Sun (2019 Nov 14)
Posted: Fri Nov 15, 2019 11:07 pm
by MarkBour
neufer wrote: ↑Thu Nov 14, 2019 10:37 pmIn the context of a distant star Mercury is ~1/285th the diameter of the Sun resulting in a temporary drop in light of ~12.34 parts per million. That amount would be extremely difficult to detect above background-level fluctuations in the star's output of about 19.5 parts per million.
A question that I find interesting here, a thought experiment I'll not be able to perform in ipsa re.
If we were to travel 1000 light years away and look back at our Solar system with a Kepler-like instrument. According to neufer, from that distance, a Mercury transit would cause a 12.34 ppm light diminution. As the Sun seems to us to have a 10 ppm natural variability, it might just be able to be detected above that. What I find interesting is wondering whether or not, once we were 1000 light years away, we might find that the Sun has more variability in our observation of its output, rising to the level of 19.5 ppm, and thus masking out swift Mercury.
neufer wrote: ↑Thu Nov 14, 2019 10:37 pmIn the context of a distant star Mercury is ~1/285th the diameter of the Sun resulting in a temporary drop in light of ~12.34 parts per million. That amount would be extremely difficult to detect above background-level fluctuations in the star's output of about 19.5 parts per million.
A question that I find interesting here, a thought experiment I'll not be able to perform in ipsa re.
If we were to travel 1000 light years away and look back at our Solar system with a Kepler-like instrument. According to neufer, from that distance, a Mercury transit would cause a 12.34 ppm light diminution. As the Sun seems to us to have a 10 ppm natural variability, it might just be able to be detected above that. What I find interesting is wondering whether or not, once we were 1000 light years away, we might find that the Sun has more variability in our observation of its output, rising to the level of 19.5 ppm, and thus masking out swift Mercury.
Why would the measured variability of the Sun change with distance? (And it is possible to detect a 10 ppm transit against 20 ppm variability. It just requires sampling enough orbits. So it might take a long time.)
neufer wrote: ↑Thu Nov 14, 2019 10:37 pmIn the context of a distant star Mercury is ~1/285th the diameter of the Sun resulting in a temporary drop in light of ~12.34 parts per million. That amount would be extremely difficult to detect above background-level fluctuations in the star's output of about 19.5 parts per million.
A question that I find interesting here, a thought experiment I'll not be able to perform in ipsa re.
If we were to travel 1000 light years away and look back at our Solar system with a Kepler-like instrument. According to neufer, from that distance, a Mercury transit would cause a 12.34 ppm light diminution. As the Sun seems to us to have a 10 ppm natural variability, it might just be able to be detected above that. What I find interesting is wondering whether or not, once we were 1000 light years away, we might find that the Sun has more variability in our observation of its output, rising to the level of 19.5 ppm, and thus masking out swift Mercury.
Why would the measured variability of the Sun change with distance? (And it is possible to detect a 10 ppm transit against 20 ppm variability. It just requires sampling enough orbits. So it might take a long time.)
As to your parenthetical comment, I'm sure you're right ... if you can get enough data and the 20 ppm variability is random, statistical analysis should be able to tease out anything that can be detected at all.
As to your question, I'm glad you asked, because it encourages me to continue my fanciful conjecture.
I don't know what lies between us and the stars that Kepler imaged. We look at those suns through the entire radius of their magnetosphere and their solar winds. Through all of the debris in their solar disks. And then through the matter floating around in the interstellar medium. We tend to think of space as the clear void through which we can see everything as it really is, but I'm suspicious of that. Another question I have is whether or not it matters in which direction one would travel. Does the Sun show more variability if viewed from its north pole, or from its equator, or neither? If viewed from > about 10 times the radius of Pluto's orbit, I would expect that viewing straight through our "planetary plane" would have more variability than viewing from above the plane.
A question that I find interesting here, a thought experiment I'll not be able to perform in ipsa re.
If we were to travel 1000 light years away and look back at our Solar system with a Kepler-like instrument. According to neufer, from that distance, a Mercury transit would cause a 12.34 ppm light diminution. As the Sun seems to us to have a 10 ppm natural variability, it might just be able to be detected above that. What I find interesting is wondering whether or not, once we were 1000 light years away, we might find that the Sun has more variability in our observation of its output, rising to the level of 19.5 ppm, and thus masking out swift Mercury.
Why would the measured variability of the Sun change with distance? (And it is possible to detect a 10 ppm transit against 20 ppm variability. It just requires sampling enough orbits. So it might take a long time.)
As to your parenthetical comment, I'm sure you're right ... if you can get enough data and the 20 ppm variability is random, statistical analysis should be able to tease out anything that can be detected at all.
As to your question, I'm glad you asked, because it encourages me to continue my fanciful conjecture. :-)
I don't know what lies between us and the stars that Kepler imaged. We look at those suns through the entire radius of their magnetosphere and their solar winds. Through all of the debris in their solar disks. And then through the matter floating around in the interstellar medium. We tend to think of space as the clear void through which we can see everything as it really is, but I'm suspicious of that. Another question I have is whether or not it matters in which direction one would travel. Does the Sun show more variability if viewed from its north pole, or from its equator, or neither? If viewed from > about 10 times the radius of Pluto's orbit, I would expect that viewing straight through our "planetary plane" would have more variability than viewing from above the plane.
I doubt that the interstellar medium, or anything lying between stars and us, represents a measurable component of variability. There's no correlation between the light curves of very close stars, as you'd expect for something in the interstellar medium. And the time scales of variability are too fast. In rare cases material in the star systems might interfere, but we get a barely measurable signal from an entire planet; the vastly lower mass (and slower variation) of distant material in the system is probably not a factor.
The question of viewing direction is more interesting. I don't think there's a difference in "conventional" variability with direction. But some variability comes from star spots, and star spots do have favored latitudes. So over the period of stellar magnetic cycles (assuming they behave in a similar way to the Sun) I can imagine that viewing from different directions might give somewhat different results.
Re: APOD: Mercury and the Quiet Sun (2019 Nov 14)
Posted: Wed Nov 20, 2019 5:10 pm
by MarkBour
Thanks for the reply, Chris. Several items of helpful info.
One in particular would seem to rule out the "interstellar medium" idea I put forth.
Chris Peterson wrote: ↑Tue Nov 19, 2019 11:15 pm
... I doubt that the interstellar medium, or anything lying between stars and us, represents a measurable component of variability. There's no correlation between the light curves of very close stars, as you'd expect for something in the interstellar medium.
I think you're saying that there's no correlation between the variability for star light curves and their distance from us (in our galaxy, on the scales we're considering). I that correct? If that has been looked at and it has been found that there is no such correlation, that's a key fact.
Mercury and the Quiet Sun
