APOD: The Solar Corona Unwrapped (2024 Apr 05)

[APOD Robot]

The Solar Corona Unwrapped

Explanation: Changes in the alluring solar corona are detailed in this creative composite image mapping the dynamic outer atmosphere of the Sun during two separate total solar eclipses. Unwrapped from the complete circle of the eclipsed Sun's edge to a rectangle and mirrored, the entire solar corona is shown during the 2017 eclipse (bottom) seen from Jackson Hole, Wyoming, and the 2023 eclipse from Exmouth, Western Australia. While the 2017 eclipse was near a minimum in the Sun's 11 year activity cycle, the 2023 eclipse was closer to solar maximum. The 2023 solar corona hints at the dramatically different character of the active Sun, with many streamers and pinkish prominences arising along the solar limb. Of course, the solar corona is only easily visible to the eye while standing in the shadow of the Moon.

<< Previous APOD

This Day in APOD

Next APOD >>

[AVAO]

The Solar Corona Unwrapped

Explanation: Changes in the alluring solar corona are detailed in this creative composite image mapping the dynamic outer atmosphere of the Sun during two separate total solar eclipses. Unwrapped from the complete circle of the eclipsed Sun's edge to a rectangle and mirrored, the entire solar corona is shown during the 2017 eclipse (bottom) seen from Jackson Hole, Wyoming, and the 2023 eclipse from Exmouth, Western Australia. While the 2017 eclipse was near a minimum in the Sun's 11 year activity cycle, the 2023 eclipse was closer to solar maximum. The 2023 solar corona hints at the dramatically different character of the active Sun, with many streamers and pinkish prominences arising along the solar limb. Of course, the solar corona is only easily visible to the eye while standing in the shadow of the Moon.

<< Previous APOD

This Day in APOD

Next APOD >>

Very cool idea with this type of representation!

...I was just wondering whether it would make sense for the rotation- or polar-axes to be in the same place. The polar axis is very easy to identify in 2017. Interestingly, for me this is no longer really that clear in the 2023 image. Does anyone know a solution for this?

Click to view full size image 1 or image 2

Click to view full size image

Image Credit & Copyright: Peter Ward (Barden Ridge Observatory)
http://www.atscope.com.au/BRO/bardenridgeobs.html

[Ann]

It looks gorgeous!

The Solar Corona Unwrapped. Image Credit & Copyright: Peter Ward (Barden Ridge Observatory)

---

It is such a beautiful, otherworldly (that's right!!!) image. Thanks to Peter Ward for producing it.

I can tell from the picture that, indeed, the solar corona behaves differently during solar minimums and solar maximums. There is definitely more turbulence "at the bottom of the corona" and more pink flares of Hα when the Sun is more active than when it is not. But since I really have so little to say about solar eclipses in general (or the solar corona), I'm just going to shut up now and stand in for Orin Stepanek and post a solar eclipse-appropriate picture of a cat!

Cat preparing for the eclipse. Credit: Hernán Seoane

---

Oh, and... Orin, I miss you.

Ann

[Roy]

Can ths be done with a coronagraph image over time, so as to highlight changes in direction and latitude of emissions?

[Christian G.]

The corona is the Sun's hidden glory! An eclipse is not just the Sun being eclipsed, it’s the corona being revealed!

[Chris Peterson]

Can ths be done with a coronagraph image over time, so as to highlight changes in direction and latitude of emissions?

To some extent, but no ground-based coronagraph can approach the dynamic range accessible during an eclipse.

One tricky point is that what we're seeing here is transient. The Sun is rotating, so we will see this entire pattern change radically over time. Over a solar cycle we would see the strength of activity change, but the actual positions of streaming material wouldn't compare much. Some statistical information could certainly be gleaned from such imagery.

[Fred the Cat]

Can ths be done with a coronagraph image over time, so as to highlight changes in direction and latitude of emissions?

To some extent, but no ground-based coronagraph can approach the dynamic range accessible during an eclipse.

One tricky point is that what we're seeing here is transient. The Sun is rotating, so we will see this entire pattern change radically over time. Over a solar cycle we would see the strength of activity change, but the actual positions of streaming material wouldn't compare much. Some statistical information could certainly be gleaned from such imagery.

To get an idea of new attempts to use ground-based coronagraphs, check out 35 minutes into the Nova that just aired.

[johnnydeep]

I suppose the Sun has no meaningfully permanent longitude map that would allow these two coronal un-wrappings to be matched up. Which makes sense since the Sun is just a ball of plasma! But I gather that the rotational north-south pole line should remain the same long term. Or does it? I know the rotational speed varies with latitude, from 24 days at the equator to 38 days at the poles

[Chris Peterson]

I suppose the Sun has no meaningfully permanent longitude map that would allow these two coronal un-wrappings to be matched up. Which makes sense since the Sun is just a ball of plasma! But I gather that the rotational north-south pole line should remain the same long term. Or does it? I know the rotational speed varies with latitude, from 24 days at the equator to 38 days at the poles

The rotational axis is fixed. But yeah... the differential rotation makes any comparison based on "longitude" meaningless. Sunspot maps and other activity metrics are all based on latitude.

[Ann]

I suppose the Sun has no meaningfully permanent longitude map that would allow these two coronal un-wrappings to be matched up. Which makes sense since the Sun is just a ball of plasma! But I gather that the rotational north-south pole line should remain the same long term. Or does it? I know the rotational speed varies with latitude, from 24 days at the equator to 38 days at the poles

The rotational axis is fixed. But yeah... the differential rotation makes any comparison based on "longitude" meaningless. Sunspot maps and other activity metrics are all based on latitude.

Solar latitudes exist. For sure.

Sunspots locations follow latitudes on the Sun. Credit: NASA's Solar Dynamics Observatory/Şenol Şanlı)

---

Ann

[Christian G.]

So, in addition to being gorgeous, requiring unique conditions to be contemplated, having a mysteriously very high temperature, a wind carrying its material that shapes the tail of our comets, gives us auroras, shields us to some extent against interstellar radiation, - what else do we owe this wonderful corona?

[johnnydeep]

I suppose the Sun has no meaningfully permanent longitude map that would allow these two coronal un-wrappings to be matched up. Which makes sense since the Sun is just a ball of plasma! But I gather that the rotational north-south pole line should remain the same long term. Or does it? I know the rotational speed varies with latitude, from 24 days at the equator to 38 days at the poles

The rotational axis is fixed. But yeah... the differential rotation makes any comparison based on "longitude" meaningless. Sunspot maps and other activity metrics are all based on latitude.

Solar latitudes exist. For sure.

Sunspots locations follow latitudes on the Sun. Credit: NASA's Solar Dynamics Observatory/Şenol Şanlı)

---

Ann

Another question about the upcoming eclipse. I know a big deal is made of how the remarkably coincidental almost exact same apparent size of the Moon and Sun allows for viewing the Sun's entire corona at once and provides the best opportunity for science to study it, but wouldn't any total eclipse where the apparent size of the Moon was greater than that of the Sun allow for just as precise a study of at least that part of the eclipse closest to the last visible portion of the Sun?

[Chris Peterson]

Another question about the upcoming eclipse. I know a big deal is made of how the remarkably coincidental almost exact same apparent size of the Moon and Sun allows for viewing the Sun's entire corona at once and provides the best opportunity for science to study it, but wouldn't any total eclipse where the apparent size of the Moon was greater than that of the Sun allow for just as precise a study of at least that part of the eclipse closest to the last visible portion of the Sun?

Sure. And as you move off the centerline you also get closer to the Sun's surface along on axis. The Moon is closer to us now than it usually is during eclipses, so appears larger than the Sun... the consequence being a very long period of totality (about 5 minutes).

[johnnydeep]

Another question about the upcoming eclipse. I know a big deal is made of how the remarkably coincidental almost exact same apparent size of the Moon and Sun allows for viewing the Sun's entire corona at once and provides the best opportunity for science to study it, but wouldn't any total eclipse where the apparent size of the Moon was greater than that of the Sun allow for just as precise a study of at least that part of the eclipse closest to the last visible portion of the Sun?

Sure. And as you move off the centerline you also get closer to the Sun's surface along on axis. The Moon is closer to us now than it usually is during eclipses, so appears larger than the Sun... the consequence being a very long period of totality (about 5 minutes).

Thanks. Are these "greater than total Solar eclipses" less common than annular ones?

[Chris Peterson]

Another question about the upcoming eclipse. I know a big deal is made of how the remarkably coincidental almost exact same apparent size of the Moon and Sun allows for viewing the Sun's entire corona at once and provides the best opportunity for science to study it, but wouldn't any total eclipse where the apparent size of the Moon was greater than that of the Sun allow for just as precise a study of at least that part of the eclipse closest to the last visible portion of the Sun?

Sure. And as you move off the centerline you also get closer to the Sun's surface along on axis. The Moon is closer to us now than it usually is during eclipses, so appears larger than the Sun... the consequence being a very long period of totality (about 5 minutes).

Thanks. Are these "greater than total Solar eclipses" less common than annular ones?

I don't know. I guess you'd have to look at all the average distances involved (Earth to Sun, Earth to Moon) and figure out whether the angular size of the Moon- on average- is larger or smaller than the Sun. Which should suggest which might be more common. FWIW, I've personally seen three annular eclipses and three total eclipses. Four if I have good conditions on Monday (which doesn't look very promising).

[alter-ego]

Sure. And as you move off the centerline you also get closer to the Sun's surface along on axis. The Moon is closer to us now than it usually is during eclipses, so appears larger than the Sun... the consequence being a very long period of totality (about 5 minutes).

Thanks. Are these "greater than total Solar eclipses" less common than annular ones?

I don't know. I guess you'd have to look at all the average distances involved (Earth to Sun, Earth to Moon) and figure out whether the angular size of the Moon- on average- is larger or smaller than the Sun. Which should suggest which might be more common. FWIW, I've personally seen three annular eclipses and three total eclipses. Four if I have good conditions on Monday (which doesn't look very promising).

Six Millenium Catalog of Solar Eclipses
 

[Chris Peterson]

Thanks. Are these "greater than total Solar eclipses" less common than annular ones?

I don't know. I guess you'd have to look at all the average distances involved (Earth to Sun, Earth to Moon) and figure out whether the angular size of the Moon- on average- is larger or smaller than the Sun. Which should suggest which might be more common. FWIW, I've personally seen three annular eclipses and three total eclipses. Four if I have good conditions on Monday (which doesn't look very promising).

Six Millenium Catalog of Solar Eclipses
 
6 Millenium Solar Eclipse Summary.jpg

Which suggests that the Moon is, on average, just a bit smaller than the Sun, slightly boosting the number of annular eclipses over total ones.

[johnnydeep]

I don't know. I guess you'd have to look at all the average distances involved (Earth to Sun, Earth to Moon) and figure out whether the angular size of the Moon- on average- is larger or smaller than the Sun. Which should suggest which might be more common. FWIW, I've personally seen three annular eclipses and three total eclipses. Four if I have good conditions on Monday (which doesn't look very promising).

Six Millenium Catalog of Solar Eclipses
 
6 Millenium Solar Eclipse Summary.jpg

Which suggests that the Moon is, on average, just a bit smaller than the Sun, slightly boosting the number of annular eclipses over total ones.

Thanks, guys!

[VictorBorun]

I suppose the Sun has no meaningfully permanent longitude map that would allow these two coronal un-wrappings to be matched up. Which makes sense since the Sun is just a ball of plasma! But I gather that the rotational north-south pole line should remain the same long term. Or does it? I know the rotational speed varies with latitude, from 24 days at the equator to 38 days at the poles

Sun's flattening is 0.00005 = 1/20,000
If we stitch a 20k pixels × 20k pixels panorama of Sun, we will know the equatorial diameter by being a pixel wider than the pole-to-pole one.

[johnnydeep]

I suppose the Sun has no meaningfully permanent longitude map that would allow these two coronal un-wrappings to be matched up. Which makes sense since the Sun is just a ball of plasma! But I gather that the rotational north-south pole line should remain the same long term. Or does it? I know the rotational speed varies with latitude, from 24 days at the equator to 38 days at the poles

Sun's flattening is 0.00005 = 1/20,000
If we stitch a 20k pixels × 20k pixels panorama of Sun, we will know the equatorial diameter by being a pixel wider than the pole-to-pole one.

Ok, but it would still not be possible to determine a fixed longitudinal coordinate since there isn't one. And this would apply to any ball of rotating gas/plasma in the center of which we are unable to find - and map - a solid core.

[VictorBorun]

I suppose the Sun has no meaningfully permanent longitude map that would allow these two coronal un-wrappings to be matched up. Which makes sense since the Sun is just a ball of plasma! But I gather that the rotational north-south pole line should remain the same long term. Or does it? I know the rotational speed varies with latitude, from 24 days at the equator to 38 days at the poles

Sun's flattening is 0.00005 = 1/20,000
If we stitch a 20k pixels × 20k pixels panorama of Sun, we will know the equatorial diameter by being a pixel wider than the pole-to-pole one.

Ok, but it would still not be possible to determine a fixed longitudinal coordinate since there isn't one. And this would apply to any ball of rotating gas/plasma in the center of which we are unable to find - and map - a solid core.

to trace a map with longitudes we must record a continuous video.
There is a clock choice problem, similar to the one for a time zone for Moon:
• more rotations counted for Sun's equator than Sun's poles
• more clock pulses counted by an atomic clock on Moon than on Earth

We will have to create a currency basket with some weights for two counts or discard one count altogether in favour of the other one.

[johnnydeep]

Sun's flattening is 0.00005 = 1/20,000
If we stitch a 20k pixels × 20k pixels panorama of Sun, we will know the equatorial diameter by being a pixel wider than the pole-to-pole one.

Ok, but it would still not be possible to determine a fixed longitudinal coordinate since there isn't one. And this would apply to any ball of rotating gas/plasma in the center of which we are unable to find - and map - a solid core.

to trace a map with longitudes we must record a continuous video.
There is a clock choice problem, similar to the one for a time zone for Moon:
• more rotations counted for Sun's equator than Sun's poles
• more clock pulses counted by an atomic clock on Moon than on Earth

We will have to create a currency basket with some weights for two counts or discard one count altogether in favour of the other one.

Hmm, I suppose that could actually work? Start recording the Sun's rotation nonstop from time T₀, and then use it to keep track. Would only be useful from that time on though.