APOD: Welcome to Perihelion (2025 Jan 04)

[APOD Robot]

Welcome to Perihelion

Explanation: Earth's orbit around the Sun is not a circle, it's an ellipse. The point along its elliptical orbit where our fair planet is closest to the Sun is called perihelion. This year perihelion is today, January 4, at 13:28 UTC, with the Earth about 147 million kilometers from the Sun. For comparison, at aphelion on last July 3 Earth was at its farthest distance from the Sun, some 152 million kilometers away. But distance from the Sun doesn't determine Earth's seasons. It's only by coincidence that the beginning of southern summer (northern winter) on the December solstice - when this H-alpha picture of the active Sun was taken - is within 14 days of Earth's perihelion date. And it's only by coincidence that Earth's perihelion date is within 11 days of the historic perihelion of NASA's Parker Solar Probe. Launched in 2018, the Parker Solar Probe flew within 6.2 million kilometers of the Sun's surface on 2024 December 24, breaking its own record for closest perihelion for a spacecraft from planet Earth.

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[Ann]

We are lucky on the northern hemisphere. When our hemisphere tilts toward the Sun in the summer, the Earth is at its greatest distance from the Sun (in July). And when our hemisphere tilts away from the Sun in the winter, the Earth is at its smallest distance from the Sun (in January).

This should make our seasons milder, or at least it seems so to me.

Ann

[Christian G.]

And to think that this:

20242112SolNeg1024.jpg

...fits 600 million times inside this!

Betelgeuse .jpg

(Betelgeuse - Xavier Hautbois, observatoire de Paris)

[Chris Peterson]

If only we could put it across, and cancel the “climate change” insanity - The SUN drives the weather!

The Sun is the energy source that powers the Earth's climate system. How that system actually operates is determined by a very large number of other, interacting features. The weather on Venus, Earth, and Mars are all driven by the Sun. Not exactly the same results! Your comment is like saying, "if only we could cancel this nonsense about semiconductors - a battery drives my computer".

[johnnydeep]

If only we could put it across, and cancel the “climate change” insanity - The SUN drives the weather!

The Sun is the energy source that powers the Earth's climate system. How that system actually operates is determined by a very large number of other, interacting features. The weather on Venus, Earth, and Mars are all driven by the Sun. Not exactly the same results! Your comment is like saying, "if only we could cancel this nonsense about semiconductors - a battery drives my computer".

Excellent analogy!

[Chris Peterson]

We are lucky on the northern hemisphere. When our hemisphere tilts toward the Sun in the summer, the Earth is at its greatest distance from the Sun (in July). And when our hemisphere tilts away from the Sun in the winter, the Earth is at its smallest distance from the Sun (in January).

This should make our seasons milder, or at least it seems so to me.

Ann

If anything, seasons in the south are milder because there's vastly more ocean in the south to moderate things. It's all very complex... the different distribution of land and water on each side of the equator, the fact that at perihelion the Earth is not just closer to the Sun, resulting in more energy hitting us, but also moving faster, resulting in a slightly shorter winter in the north and a slightly longer summer in the south. And, from a climate (as opposed to weather) standpoint, our varying distance from the Sun modulates major ocean currents, which are major drivers of regional climate and weather patterns.

[johnnydeep]

And to think that this:
20242112SolNeg1024.jpg
...fits 600 million times inside this!
Betelgeuse .jpg
(Betelgeuse - Xavier Hautbois, observatoire de Paris)

And to think that 109 Earths are needed to span the Sun! (And 1,300,000 are needed to fill its volume.)

Click to view full size image

[Christian G.]

And to think that this:
20242112SolNeg1024.jpg
...fits 600 million times inside this!
Betelgeuse .jpg
(Betelgeuse - Xavier Hautbois, observatoire de Paris)

And to think that 109 Earths are needed to span the Sun! (And 1,300,000 are needed to fill its volume.)

Click to view full size image

Crazy! This means Betelgeuse could take in over 600 trillion Earths!

[johnnydeep]

And to think that this:
20242112SolNeg1024.jpg
...fits 600 million times inside this!
Betelgeuse .jpg
(Betelgeuse - Xavier Hautbois, observatoire de Paris)

And to think that 109 Earths are needed to span the Sun! (And 1,300,000 are needed to fill its volume.)

Click to view full size image

Crazy! This means Betelgeuse could take in over 600 trillion Earths!

Of course, the larger and less dense these spheres of star stuff get, the harder it is to define where their "surfaces" end and interstellar space begins.

[florid_snow]

I've been reading about tides after some interesting comments from Chris the other day. So the squishing of Earth that causes the tides is stronger when we are closer to the Sun, because the tidal squish is about the gradient of the gravity field. That's why it's stronger at Full and New Moon when the Moon's gravity squishes us along the same axis as the Sun. Apparently many people call it "King" tides during the strongest tides of the year, in early January, whenever the moon is full or new. Similarly strong king tides can also occur any time of year if the moon's closest approach is aligned with the New or Full time of the month.

But I wonder if there is also a 12 year cycle with Jupiter's orbit, because it causes the solar system barycenter to be close to the edge of the Sun? This would put the sun maybe a full solar diameter closer to us during perihelion? Putting together the numbers we've been discussing about this APOD, the distance change from July to January is 152 - 147 million kilometers, or a total change of 5 million km (5 gigameters). And the diameter of the Sun is 109 Earths, which is equal to about 1.39 million kilometers, or 1.4 gigameters. So the 12 year cycle of the Jupiter-Sun orbit could potentially affect the Earth-Sun perihelion distance by 1.4/5 = 28%? I don't know the dimensionality of the tidal effect wrt distance change, but it seems like a significant fraction of the distance change to me. What do you think?

tides02.jpg

[Christian G.]

Of course, the larger and less dense these spheres of star stuff get, the harder it is to define where their "surfaces" end and interstellar space begins.

Indeed. For instance in this image we see Antares stuff extending a huge 12 times further out than its "official" radius! Which itself can vary by as much as 20%. Not easy to keep up with these humongous unstable stars!

A.jpg

Credit: NRAO/AUI/NSF, S. Dagnello

[Ann]

The ginormous red supergiants are very far from perfectly spherical:

Snapshots from a simulation of Betelgeuse showing how convection dominates its surface. At right, blue patches show regions of Betelgeuse moving away from Earth, red regions are areas moving toward Earth. (Image credit: MPA/Ma, Jing-Ze et al)

---

I found a great simulation of the boiling surface of Betelgeuse. I can't copy it, but I really recommend that you watch it:

https://www.livescience.com/space/astro ... ng-surface

Ann

[Christian G.]

The ginormous red supergiants are very far from perfectly spherical:

Snapshots from a simulation of Betelgeuse showing how convection dominates its surface. At right, blue patches show regions of Betelgeuse moving away from Earth, red regions are areas moving toward Earth. (Image credit: MPA/Ma, Jing-Ze et al)

---

I found a great simulation of the boiling surface of Betelgeuse. I can't copy it, but I really recommend that you watch it:

https://www.livescience.com/space/astro ... ng-surface

Ann

Great recommendation! The simulation looks like Betelgeuse's final hour! Talk about a tumultuous surface… And apparently, whereas the Sun's bubbles or granules are about the size of Texas, those of Betelgeuse are the size of Earth's orbit! And move up and down at some 30 km/sec!

[Christian G.]

The ginormous red supergiants are very far from perfectly spherical:

Snapshots from a simulation of Betelgeuse showing how convection dominates its surface. At right, blue patches show regions of Betelgeuse moving away from Earth, red regions are areas moving toward Earth. (Image credit: MPA/Ma, Jing-Ze et al)

---

I found a great simulation of the boiling surface of Betelgeuse. I can't copy it, but I really recommend that you watch it:

https://www.livescience.com/space/astro ... ng-surface

Ann

Here you can find the complete simulation video and it's fascinating! (the last one on the list, "video summary for general audience")
https://zenodo.org/records/10824649

[Ann]

The ginormous red supergiants are very far from perfectly spherical:

Snapshots from a simulation of Betelgeuse showing how convection dominates its surface. At right, blue patches show regions of Betelgeuse moving away from Earth, red regions are areas moving toward Earth. (Image credit: MPA/Ma, Jing-Ze et al)

---

I found a great simulation of the boiling surface of Betelgeuse. I can't copy it, but I really recommend that you watch it:

https://www.livescience.com/space/astro ... ng-surface

Ann

Here you can find the complete simulation video and it's fascinating! (the last one on the list, "video summary for general audience")
https://zenodo.org/records/10824649

Really fascinating, Christian! Thanks!

So they don't know if Betelgeuse is rotating? My amateur gut reaction is that the core of Betelgeuse "should" be rotating. But does that mean that the swollen outer layers are also rotating? The core of Betelgeuse is extremely small and hot, much, much smaller and hotter than the core of the Sun, but the outer layers are incredibly puffed up, tenuous and swollen. Do the outer layers really have to rotate just because the tiny core, so far away, does?

Ann

[Chris Peterson]

The ginormous red supergiants are very far from perfectly spherical:

Snapshots from a simulation of Betelgeuse showing how convection dominates its surface. At right, blue patches show regions of Betelgeuse moving away from Earth, red regions are areas moving toward Earth. (Image credit: MPA/Ma, Jing-Ze et al)

---

I found a great simulation of the boiling surface of Betelgeuse. I can't copy it, but I really recommend that you watch it:

https://www.livescience.com/space/astro ... ng-surface

Ann

Here you can find the complete simulation video and it's fascinating! (the last one on the list, "video summary for general audience")
https://zenodo.org/records/10824649

Really fascinating, Christian! Thanks!

So they don't know if Betelgeuse is rotating? My amateur gut reaction is that the core of Betelgeuse "should" be rotating. But does that mean that the swollen outer layers are also rotating? The core of Betelgeuse is extremely small and hot, much, much smaller and hotter than the core of the Sun, but the outer layers are incredibly puffed up, tenuous and swollen. Do the outer layers really have to rotate just because the tiny core, so far away, does?

Ann

Ann

Betelgeuse is most certainly rotating. There is no way it couldn't be. The suggestion is that a kind of illusion is making it appear to be rotating faster than it actually is.