APOD: Milky Way Behind Three Merlons (2024 Aug 07)

[APOD Robot]

Milky Way Behind Three Merlons

Explanation: To some, they look like battlements, here protecting us against the center of the Milky Way. The Three Merlons, also called the Three Peaks of Lavaredo, stand tall today because they are made of dense dolomite rock which has better resisted erosion than surrounding softer rock. They formed about 250 million years ago and so are comparable in age with one of the great extinctions of life on Earth. A leading hypothesis is that this great extinction was triggered by an asteroid about 10-km across, larger in size than Mount Everest, impacting the Earth. Humans have gazed up at the stars in the Milky Way and beyond for centuries, making these battlefield-like formations, based in the Sexten Dolomites, a popular place for current and ancient astronomers.

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[Ann]

Yes, I like it!

Milky Way Behind Three Merlons. Image Credit & Copyright: Donato Lioce

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What I like best about it is that you could almost imagine that this image is not a composite image at all (it is, of course), because the faint light of the Milky Way could almost have illuminated the mountainscape on its own.

But you can actually tell from the color of the image that the foreground has not been photographed by the light of the Milky Way:

As you can see, the dominant light of the Milky Way is yellowish, but the (probably neutral-colored) slopes behind the Three Merlons are seen to be a mostly non-yellow shade of gray.


Anyway. The idea of the Milky Way as a light source on the Earth reminds me of the scarab beetles which roll their dung balls in straight lines at night by navigating by the stars. But because these little critters can't tell one star or constellation from another, they navigate by the light of the Milky Way.

The scarab beetle uses the light of the Milky Way to keep it on a straight course. Credit: Jacqueline MoenImage via Current Biology, Dacke et. al.

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Smithsonian Magazine wrote:

Science has shown us that a number of organisms use the stars for navigation: songbirds, harbor seals and, of course, humans. But a new study by a team of Swedish and South African researchers published today in the journal Current Biology indicates that a rather unexpected creature can be added to this list—the lowly dung beetle.

So I suppose that the Arctic Tern, the wold's longest-flying migrating bird, does the same during its incredible journey from pole to pole every year. Navigate by the light of the Milky Way, I mean.

This bird over the Milky Way is not an Arctic Tern, but I was the best I could do.

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Unless they are born knowing how to find Polaris in the sky, of course!

Polaris. It's not nearly as bright as this, of course. Credit: Possibly Ian Lauer Astro

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Ann

[Eric]

Thank you for posting this nice image, Otto.
Copyediting note: The asteroid diameter should read "10 km", not "10-km". Hyphenation would be used for the adjectival form, e.g. "One day, the Vogons sent a 10-km asteroid to the Earth, and thereby saved the cetaceans from the humans".

[Roy]

Following the link to the Permian extinction, we are given asteroid “as big as Everest” estimates from 6 to 12 km diameter. This ( V = 4/3 x pi x r*2 ) which calculates from 112.8 to 902.5 cubic kilometers, a wide range. Supposing it to be of granite, density ~ 2.7 grams per cc, the mass ranges from 3.05 x 10*11 to 2.44 x 10*11 tonnes.
Asteroids striking the earth move from 13.5 to 17 km/sec. Kinetic energy is e = mv*2. So low mass x low velocity estimate is 5,56 x10*13 ; high mass x high velocity is 7.05 x 10*14. Units are tonne x km*2 / sec*2, and I don’t know what that is, much less what 7 million billion of them are. Megatons, based on the force of detonating a ton of TNT is a totally inadequate comparison.

However, there is a 500 km wide crater in Wilkes Land thought to be contemporaneous with the Permian extinction, ICMYI.

[Roy]

SB 3.05 x 10*11 to 2.44 x 10*12 tonnes.

[johnnydeep]

Yes, I like it!

Milky Way Behind Three Merlons. Image Credit & Copyright: Donato Lioce

---

What I like best about it is that you could almost imagine that this image is not a composite image at all (it is, of course), because the faint light of the Milky Way could almost have illuminated the mountainscape on its own.

But you can actually tell from the color of the image that the foreground has not been photographed by the light of the Milky Way:


APOD 8 July 2024 detail.png


As you can see, the dominant light of the Milky Way is yellowish, but the (probably neutral-colored) slopes behind the Three Merlons are seen to be a mostly non-yellow shade of gray.


Anyway. The idea of the Milky Way as a light source on the Earth reminds me of the scarab beetles which roll their dung balls in straight lines at night by navigating by the stars. But because these little critters can't tell one star or constellation from another, they navigate by the light of the Milky Way.

...

Ann

But the light of the MW is behind those visible slopes! I suppose you're considering that the arc of the MW extends overhead and eventually does illuminate those slopes?

[Christian G.]

Beautiful image. All the realms are present, the biologic, the geologic, the cosmic…

As in this painting by Caspar David Friedrich, which somehow came to mind:

[Chris Peterson]

Following the link to the Permian extinction, we are given asteroid “as big as Everest” estimates from 6 to 12 km diameter. This ( V = 4/3 x pi x r*2 ) which calculates from 112.8 to 902.5 cubic kilometers, a wide range. Supposing it to be of granite, density ~ 2.7 grams per cc, the mass ranges from 3.05 x 10*11 to 2.44 x 10*11 tonnes.
Asteroids striking the earth move from 13.5 to 17 km/sec. Kinetic energy is e = mv*2. So low mass x low velocity estimate is 5,56 x10*13 ; high mass x high velocity is 7.05 x 10*14. Units are tonne x km*2 / sec*2, and I don’t know what that is, much less what 7 million billion of them are. Megatons, based on the force of detonating a ton of TNT is a totally inadequate comparison.

However, there is a 500 km wide crater in Wilkes Land thought to be contemporaneous with the Permian extinction, ICMYI.

The formula for volume is with the radius cubed, which you clearly used but didn't write above. A more realistic mass for an asteroid is probably around 1 gm/cm³, but the much bigger factor with kinetic energy is the speed, of course. In this case it can range from a low of 11 km/s to a high of 72 km/s (much higher than the number you used). Taking the worst case situation for both speed and mass, we get a collision energy of around 10²⁵ J, or 2 billion megatons of TNT. Not a good day to be around.

[Ann]

Yes, I like it!

Milky Way Behind Three Merlons. Image Credit & Copyright: Donato Lioce

---

What I like best about it is that you could almost imagine that this image is not a composite image at all (it is, of course), because the faint light of the Milky Way could almost have illuminated the mountainscape on its own.

But you can actually tell from the color of the image that the foreground has not been photographed by the light of the Milky Way:


APOD 8 July 2024 detail.png


As you can see, the dominant light of the Milky Way is yellowish, but the (probably neutral-colored) slopes behind the Three Merlons are seen to be a mostly non-yellow shade of gray.


Anyway. The idea of the Milky Way as a light source on the Earth reminds me of the scarab beetles which roll their dung balls in straight lines at night by navigating by the stars. But because these little critters can't tell one star or constellation from another, they navigate by the light of the Milky Way.

...

Ann

But the light of the MW is behind those visible slopes! I suppose you're considering that the arc of the MW extends overhead and eventually does illuminate those slopes?

Well, I was thinking that the yellow light of the Milky Way should illuminate some parts of the foreground and make it yellower in color than the parts that are in shadow. But it doesn't.

Ann