APOD: A Space Station Crosses a Busy Sun (2022 Apr 11)

[APOD Robot]

A Space Station Crosses a Busy Sun

Explanation: Typically, the International Space Station is visible only at night. Slowly drifting across the night sky as it orbits the Earth, the International Space Station (ISS) can be seen as a bright spot several times a year from many locations. The ISS is then visible only just after sunset or just before sunrise because it shines by reflected sunlight -- once the ISS enters the Earth's shadow, it will drop out of sight. The only occasion when the ISS is visible during the day is when it passes right in front of the Sun. Then, it passes so quickly that only cameras taking short exposures can visually freeze the ISS's silhouette onto the background Sun. The featured picture did exactly that -- it is actually a series of images taken earlier this month from Beijing, China with perfect timing. This image series was later combined with separate images taken at nearly the same time but highlighting the texture and activity on the busy Sun. The solar activity included numerous gaseous prominences seen around the edge, highlighted in red, filaments seen against the Sun's face, and a dark sunspot.

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[VictorBorun]

"The only occasion when the ISS is visible during the day "?
Come on!
Just take a day with half-a-disk Moon and Sun in the sky and go to a location where the ISS will eclipse the Moon!

I think you will get to see how passing the terminator line the ISS will change between dark shadow details against Moon's dayside part and bright sunlit details against Moon's nightside part.

You can subtract the sky shine and get a high contrast picture, with Moon against the black sky.
But even if you don't, you can still see Moon's dayside part through the sky shine.
Therefore you can still see the ISS, too

[orin stepanek]

I love these captured crossings of the space station eclipsing the sun
on occasion !

Kitty love!

[Dan]

"This image series was later combined with separate images..."

More compositing? In other words, more temporal deformity...

[Chris Peterson]

"This image series was later combined with separate images..."

More compositing? In other words, more temporal deformity...

Given that all of the images were taken at the same time with respect to the rate that anything was changing on the Sun, there is no visible "deformity". You might as well make that complaint about images taken with your phone or most modern digital cameras, which also combine pictures taken at different times to produce the final result.

[mister T]

Are you sure That is not a TIE fighter?

[Chris Peterson]

"The only occasion when the ISS is visible during the day "?
Come on!
Just take a day with half-a-disk Moon and Sun in the sky and go to a location where the ISS will eclipse the Moon!

I think you will get to see how passing the terminator line the ISS will change between dark shadow details against Moon's dayside part and bright sunlit details against Moon's nightside part.

You can subtract the sky shine and get a high contrast picture, with Moon against the black sky.
But even if you don't, you can still see Moon's dayside part through the sky shine.
Therefore you can still see the ISS, too

The sky is much brighter than the shadowed part of the Moon. You can't subtract it out and see that part during the day. Normally, the ISS itself is brighter than the sunlit face of the Moon, so if you image it crossing the Moon during the day, you'll see it as a bright object, not a silhouette. (See http://www.cloudbait.com/20200604_iss-moon.php as an example.) Which means you'll also see it against the shadowed part of the Moon... but the Moon itself will be invisible, indistinguishable from the sky.

[xuxa]

LOL reminds me of the "id police" stamp roller thing they sell on tv. ;o)

[De58te]

Speaking of temporal deformity, I don't think any of the Apod pictures are live. I mean photographed in this exact time called The Present. Suppose I had waited an hour from now to sign on. Would the live Sun still look like that? I mean usually as the day goes on that the sun gets brighter from the orange of sunrise to a bright yellow, to a blinding white of high noon. And even when I look at the sun at sunrise when it is that orange, It is usually smaller than what it is on the screen, and I rarely see those sunspots and prominences on the side. It usually is just a smooth orange. So what is the real form and what is the deformity?

[Chris Peterson]

Speaking of temporal deformity, I don't think any of the Apod pictures are live. I mean photographed in this exact time called The Present. Suppose I had waited an hour from now to sign on. Would the live Sun still look like that? I mean usually as the day goes on that the sun gets brighter from the orange of sunrise to a bright yellow, to a blinding white of high noon. And even when I look at the sun at sunrise when it is that orange, It is usually smaller than what it is on the screen, and I rarely see those sunspots and prominences on the side. It usually is just a smooth orange. So what is the real form and what is the deformity?

Just "looking" alone introduces massive "deformity", no? We need look no further than all the images of things made in wavelengths that our eyes cannot perceive.

[Ann]

A tidbit here:

The Sun used to be the roundest object in the Universe. (Not that we have a census of all the stars in the Universe, at least not yet. )

The Guardian wrote in 2012:

The sun is the most perfectly round natural object known in the universe, say scientists who have conducted precise measurements of its dimensions.

As a spinning ball of gas, astronomers had always expected our nearest star to bulge slightly at its equator, making it very slightly flying-saucer shaped. The planet Jupiter demonstrates this effect well. Its high rate of spin - once every 10 hours - means that it is almost 7% wider across its equator than the distance from pole to pole.

Now a team led by the University of Hawaii's Dr Jeffrey Kuhn have made the first precise measurement of the sun's equatorial bulge, or its "oblateness". The results were a big surprise. "We were shocked," says Kuhn. The sun doesn't bulge much at all. It is 1.4m kilometres across, but the difference between its diameter at the equator and between the poles is only 10 kilometres.

Scaled to the size of a beachball, that difference is less than the width of a human hair. Only an artificial sphere of silicon that was created as a standard for weights is known to be more perfectly spherical.

But a few years later another champion of perfect natural roundness was found:

Image credit: © Laurent Gizon et al. and the Max Planck Institute for
Solar System Research, Germany. Illustration by Mark A. Garlick.

Sci News wrote:

Kepler 11145123, a slowly rotating star roughly 5,000 light-years away, is the most spherical natural object ever measured, more spherical than the Sun, says an international team of astronomers.

The team, led by Dr. Laurent Gizon, an astronomer with the Max Planck Institute for Solar System Research and the University of Göttingen, was able to measure the oblateness of Kepler 11145123 using asteroseismology – the study of the oscillations of stars.

The technique revealed that the difference between the equatorial and polar radii of the star is only 3 km – a number that is surprisingly small compared to the star’s mean radius of 1.5 million km.

“This makes Kepler 11145123 the roundest natural object ever measured, even more round than the Sun,” Dr. Gizon said.

Asteroseismic measurement of surface-to-core rotation in a main-sequence A star, KIC 11145123

So the Sun is no longer the champion of cosmic sphericity. But even though dear old Sol looks kind of spotty and knotty in today's APOD, it is nevertheless pretty darn evenly spherical!

Ann

[Chris Peterson]

A tidbit here:

The Sun used to be the roundest object in the Universe. :shock: (Not that we have a census of all the stars in the Universe, at least not yet. :wink: )

The roundest natural object!

[johnnydeep]

A tidbit here:

The Sun used to be the roundest object in the Universe. (Not that we have a census of all the stars in the Universe, at least not yet. )

The roundest natural object!

Neutron stars? I thought they at least hold the record for smoothness. But perhaps only the ones that don't rotate very fast are also as close to perfect spheres as we can get. Although this recent article give an update on the smoothness - https://www.newscientist.com/article/dn ... han-steel/

The stronger crust means a neutron star [with a 20 km diameter] can support a larger bulge than thought – a “mountain” could rise some 10 centimetres above the surface, stretching over several kilometres.

So, the surface bulges would only be 1 part in 200,000, or .0005 %. How does that compare to the smoothest man made sphere? I suppose someone must have made one with surface "mountains" only an atom or two high...

[Chris Peterson]

A tidbit here:

The Sun used to be the roundest object in the Universe. :shock: (Not that we have a census of all the stars in the Universe, at least not yet. :wink: )

The roundest natural object!

Neutron stars? I thought they at least hold the record for smoothness. But perhaps only the ones that don't rotate very fast are also as close to perfect spheres as we can get. Although this recent article give an update on the smoothness - https://www.newscientist.com/article/dn ... han-steel/

The stronger crust means a neutron star [with a 20 km diameter] can support a larger bulge than thought – a “mountain” could rise some 10 centimetres above the surface, stretching over several kilometres.

So, the surface bulges would only be 1 part in 200,000, or .0005 %. How does that compare to the smoothest man made sphere? I suppose someone must have made one with surface "mountains" only an atom or two high...

The spheres used in the Gravity Probe B gyros were spherical to 1 part in 5.3 million. That's a bit ahead of the silicon sphere that was constructed as a kilogram standard in an (abandoned) attempt to redefine the kilogram. And both well ahead of a neutron star.

[Fred the Cat]

Atlantis docking as ISS transits the sun. It seems a tough image to plan. Or was it good and lucky

[MarkBour]

...
Normally, the ISS itself is brighter than the sunlit face of the Moon, so if you image it crossing the Moon during the day, you'll see it as a bright object, not a silhouette. (See http://www.cloudbait.com/20200604_iss-moon.php as an example.) Which means you'll also see it against the shadowed part of the Moon... but the Moon itself will be invisible, indistinguishable from the sky.

Loved that sequence you got of the sunlit ISS crossing the moon!

Looking at it as closely as I can, the images appear to change shape and color from frame to frame. No idea why, though.

[angray]

I'm intrigued by the unevenness of the ISS images. Some variation in shutter speed would explain the different distances between each image, but shouldn't they all line up on the same center-line?

[Chris Peterson]

...
Normally, the ISS itself is brighter than the sunlit face of the Moon, so if you image it crossing the Moon during the day, you'll see it as a bright object, not a silhouette. (See http://www.cloudbait.com/20200604_iss-moon.php as an example.) Which means you'll also see it against the shadowed part of the Moon... but the Moon itself will be invisible, indistinguishable from the sky.

Loved that sequence you got of the sunlit ISS crossing the moon!

Looking at it as closely as I can, the images appear to change shape and color from frame to frame. No idea why, though.

The Moon was only 11° above the horizon, so I was looking through a lot of air. Basically, the ISS was "twinkling". The low Moon also means the ISS was far away- about 1500 km, compared with just 420 km if it were overhead.

[Chris Peterson]

I'm intrigued by the unevenness of the ISS images. Some variation in shutter speed would explain the different distances between each image, but shouldn't they all line up on the same center-line?

An optical illusion caused by the sort of random dot pattern created by granulation or by the odd shape and angle of the ISS. The distance between images varies by less than 10%, and the deviation from linear by no more than 2 or 3 pixels.

(It's possible that the sequence was faster than we see here, and intermediate images were selected for sharpness, which could increase the dither in spacing.)
_

[VictorBorun]

"The only occasion when the ISS is visible during the day "?
Come on!

The sky is much brighter than the shadowed part of the Moon. You can't subtract it out and see that part during the day. Normally, the ISS itself is brighter than the sunlit face of the Moon, so if you image it crossing the Moon during the day, you'll see it as a bright object, not a silhouette. (See http://www.cloudbait.com/20200604_iss-moon.php as an example.) Which means you'll also see it against the shadowed part of the Moon... but the Moon itself will be invisible, indistinguishable from the sky.

I can see now that a low Moon is bad because the ISS is distant and the air is thick.
Still you can use a zenith quarter-disk Moon with a 45° high Sun to get a daytime pic.
The ISS sunlit details will be small, but the rest will be seen too, dark against Moon's day's part?

[Chris Peterson]

"The only occasion when the ISS is visible during the day "?
Come on!

The sky is much brighter than the shadowed part of the Moon. You can't subtract it out and see that part during the day. Normally, the ISS itself is brighter than the sunlit face of the Moon, so if you image it crossing the Moon during the day, you'll see it as a bright object, not a silhouette. (See http://www.cloudbait.com/20200604_iss-moon.php as an example.) Which means you'll also see it against the shadowed part of the Moon... but the Moon itself will be invisible, indistinguishable from the sky.

I can see now that a low Moon is bad because the ISS is distant and the air is thick.
Still you can use a zenith quarter-disk Moon with a 45° high Sun to get a daytime pic.
The ISS sunlit details will be small, but the rest will be seen too, dark against Moon's day's part?

I'm not sure I understand. I think the only time we will ever see the ISS silhouetted against the Moon is when the ISS is not in sunlight. Otherwise it will be brighter.

[VictorBorun]

I mean with just 45° between Sun and the ISS, most of the details will be dark, will not they?

[Fred the Cat]

A transit from another planet.

[johnnydeep]

A transit from another planet.

Very cool! [ PS - you can use the "youtube" button to provide a much nicer link to a video, complete with an embedded player and thumbnail. ]

[Fred the Cat]

A transit from another planet.

Very cool! [ PS - you can use the "youtube" button to provide a much nicer link to a video, complete with an embedded player and thumbnail. ]

Yes I should become more creative with the tools available. It's not like I'm stuck in a box.