APOD: Rocket Transits Rippling Sun (2022 May 31)

[APOD Robot]

Rocket Transits Rippling Sun

Explanation: The launch of a rocket at sunrise can result in unusual but intriguing images that feature both the rocket and the Sun. Such was the case last month when a SpaceX Falcon 9 rocket blasted off from NASA's Kennedy Space Center carrying 53 more Starlink satellites into low Earth orbit. In the featured launch picture, the rocket's exhaust plume glows beyond its projection onto the distant Sun, the rocket itself appears oddly jagged, and the Sun's lower edge shows peculiar drip-like ripples. The physical cause of all of these effects is pockets of relatively hot or rarefied air deflecting sunlight less strongly than pockets relatively cool or compressed air: refraction. Unaware of the Earthly show, active sunspot region 3014 -- on the upper left -- slowly crosses the Sun.

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[orin stepanek]

The sun looks a fuzzy tennis ball!

Now that is fire power!

.jpg (10.33 KiB) Viewed 8731 times

We seen these guys before!

[Ann]

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Rocket Transits Rippling Sun. Image Credit & Copyright: Michael Cain

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I tried to place the plus signs between the images so that the sequence would be, burnt-out matchstick + yellow disk + black background = today's APOD.

Ann

I guess there is a bit more to today's APOD than a burnt-out matchstick, a yellow disk and a black background, eh?

[Wadsworth]

The sperm swimming towards the egg.
Are we fertilizing space?

[m.clayton]

Is anyone else reminded of an egg and sperm?

[hubert@hubwest.com]

The mostly vertical ripples at the bottom limb of the Sun are interesting. My guess is that these are caused by sound waves from the rocket. These would make somewhat cylindrical shock waves surrounding the rocket's path, leading to the vertical structures seen in the image.

[johnnydeep]

The mostly vertical ripples at the bottom limb of the Sun are interesting. My guess is that these are caused by sound waves from the rocket. These would make somewhat cylindrical shock waves surrounding the rocket's path, leading to the vertical structures seen in the image.

Not sure about that. If it's sound, why aren't there ripples at the top of the Sun as well?

[owlice]

carrying 53 more Starlink satellites into low Earth orbit

Robbing us all of the night sky.

[Ann]

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Since everybody is so interested (yes, I know you are ) I can inform you that the dominant wavelength of the Sun in today's APOD is most likely 593 nm, ████, corresponding to RGB values of R = 255, G = 213 and B = 0.

Of course the Sun is nowhere near as yellow-orange as that. Let's compare the Sun with Capella, the luminary of constellation Auriga:

In the above picture (and I'm sorry I don't know the name of the author), Capella is located at far left. Does it look yellow to you? Yes, I admit, it does look yellow-white, and so it should, because it is yellower than the Sun. The B-V index of Capella is + 0.795, whereas the B-V index of the Sun is + 0.656. And the larger the B-V index is, the yellower (or even redder) is the star. So the Sun is whiter than Capella, and Capella isn't very yellow!

The 25 brightest stars in the night sky. Photos: Tragoolchitr Jittasaiyapan

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This may be the color of Capella: ████

And some may argue that it is the color of the Sun as well. Whatever.

Ann

[VictorBorun]

Since everybody is so interested (yes, I know you are ) I can inform you that the dominant wavelength of the Sun in today's APOD is most likely 593 nm, ████, corresponding to RGB values of R = 255, G = 213 and B = 0.
Of course the Sun is nowhere near as yellow-orange as that.

the posted pic is more about the sky than the space.
The disk of the sun is low here so the blue is scattered to sky dayshine (black at this 1/32000 sec exposure) and the disk is tinted.
However the disk of the sun is redder at edges where the photosphere is seen as thicker and its redder outer layer is less transparent

By the way I take it the exhaust is hot and low-density, bending light like a concave lens and thus looks black.
At an ordinary exposure the exhaust is not black:

[MarkBour]

The mostly vertical ripples at the bottom limb of the Sun are interesting. My guess is that these are caused by sound waves from the rocket. These would make somewhat cylindrical shock waves surrounding the rocket's path, leading to the vertical structures seen in the image.

Not sure about that. If it's sound, why aren't there ripples at the top of the Sun as well?

Because the rocket is moving rapidly? If it is supersonic, there could not be any sound waves above it. Even if subsonic, but fast, the sound waves would be behind more than in front.

[hubert@hubwest.com]

no ripples at the top because the craft is already supersonic

[Chris Peterson]

no ripples at the top because the craft is already supersonic

My first thought, as well. But no. The photographer was about 20 km from the launch, and the Sun was 5° above the horizon. So the vehicle altitude was 1.7 km, at which point its speed was 500 km/h (139 m/s). It became supersonic (1100 km/h, 305 m/s) when it reached an altitude of 8 km.

[johnnydeep]

no ripples at the top because the craft is already supersonic

My first thought, as well. But no. The photographer was about 20 km from the launch, and the Sun was 5° above the horizon. So the vehicle altitude was 1.7 km, at which point its speed was 500 km/h (139 m/s). It became supersonic (1100 km/h, 305 m/s) when it reached an altitude of 8 km.

So even if the rocket was not supersonic yet, would the fact that the sound waves are more compressed at the top than the bottom explain the lack of ripples at the top of the sun?

[MarkBour]

no ripples at the top because the craft is already supersonic

My first thought, as well. But no. The photographer was about 20 km from the launch, and the Sun was 5° above the horizon. So the vehicle altitude was 1.7 km, at which point its speed was 500 km/h (139 m/s). It became supersonic (1100 km/h, 305 m/s) when it reached an altitude of 8 km.

So even if the rocket was not supersonic yet, would the fact that the sound waves are more compressed at the top than the bottom explain the lack of ripples at the top of the sun?

https://www.youtube.com/watch?v=RtzG-l7lEfk
Is a lengthy old film on the sound barrier. Mainly, it shows the effect that I guessed might have been happening in the APOD -- the sound waves not being able to get much ahead of the rocket's nozzle.

And similarly, from LIVESCIENCE.COM:

https://www.livescience.com/63030-rocke ... n-dog.html
Despite what the video's title says, the rocket here is not quite traveling at supersonic speeds; if it was, the vehicle's sound waves would be falling behind the rocket in a cone shape, not blasting out in front of it like a ripple.

Here's a great photo that is similar to the APOD in a way:

https://petapixel.com/2022/05/16/navy-f ... -of-sound/

Chris determined that the rocket was only moving at about mach 0.5 at the time of the photograph.

When I re-examine the image of this APOD, I would say that the waves (seen as refraction of the edge of the solar disk) are larger and more pronounced below the rocket's nozzle, but they do appear somewhat above it, diminishing in wavelength and in amplitude, nearly to the top of the Sun.

An alternative thought (perhaps this is what you were thinking) is that it's more like the wake of a boat and is something spreading more slowly than the speed of sound.
https://www.youtube.com/watch?v=95sQcSulRFM
As the narration for the above indicates, the waves in a boat's wake are much slower than the speed of sound in water. But they're also not compression waves.

The wake of a submarine would be a better match, since the rocket is surrounded in 3D by the air. Surely the rocket is producing a wake of some sort. But in the air, any such waves are surely compression waves, so I think that once moving on their own, they always travel at the speed of sound. As this little article seems to imply:
https://howthingsfly.si.edu/aerodynamics/waves-air

Two notes that I think are correct, but that I also don't know much about: (1) The molecules in the air that are passing the compression waves on are not moving the same as the wave itself. (2) A wavefront can progress at a different speed than the speed of the wave itself, depending on how it is measured.

[johnnydeep]

My first thought, as well. But no. The photographer was about 20 km from the launch, and the Sun was 5° above the horizon. So the vehicle altitude was 1.7 km, at which point its speed was 500 km/h (139 m/s). It became supersonic (1100 km/h, 305 m/s) when it reached an altitude of 8 km.

So even if the rocket was not supersonic yet, would the fact that the sound waves are more compressed at the top than the bottom explain the lack of ripples at the top of the sun?

https://www.youtube.com/watch?v=RtzG-l7lEfk
Is a lengthy old film on the sound barrier. Mainly, it shows the effect that I guessed might have been happening in the APOD -- the sound waves not being able to get much ahead of the rocket's nozzle.

And similarly, from LIVESCIENCE.COM:

https://www.livescience.com/63030-rocke ... n-dog.html
Despite what the video's title says, the rocket here is not quite traveling at supersonic speeds; if it was, the vehicle's sound waves would be falling behind the rocket in a cone shape, not blasting out in front of it like a ripple.

Here's a great photo that is similar to the APOD in a way:

Capture2.png

https://petapixel.com/2022/05/16/navy-f ... -of-sound/

Chris determined that the rocket was only moving at about mach 0.5 at the time of the photograph.

When I re-examine the image of this APOD, I would say that the waves (seen as refraction of the edge of the solar disk) are larger and more pronounced below the rocket's nozzle, but they do appear somewhat above it, diminishing in wavelength and in amplitude, nearly to the top of the Sun.

An alternative thought (perhaps this is what you were thinking) is that it's more like the wake of a boat and is something spreading more slowly than the speed of sound.
https://www.youtube.com/watch?v=95sQcSulRFM
As the narration for the above indicates, the waves in a boat's wake are much slower than the speed of sound in water. But they're also not compression waves.

The wake of a submarine would be a better match, since the rocket is surrounded in 3D by the air. Surely the rocket is producing a wake of some sort. But in the air, any such waves are surely compression waves, so I think that once moving on their own, they always travel at the speed of sound. As this little article seems to imply:
https://howthingsfly.si.edu/aerodynamics/waves-air

Two notes that I think are correct, but that I also don't know much about: (1) The molecules in the air that are passing the compression waves on are not moving the same as the wave itself. (2) A wavefront can progress at a different speed than the speed of the wave itself, depending on how it is measured.

Thanks, Mark.