Astronomy Picture of the Day

MikeDYur

This had caught my eye as quite an achievement, a mosaic photo of the far side of our moon.



http://antwrp.gsfc.nasa.gov/apod/ap161230.html

rjo__

Looks like a massive asteroid embedded itself on the surface... at about 10 o'clock position.

Clock Loop

Back and .,...... front.









Commence discussion.

MikeDYur

It may be our prospective but, it looks like impact creators are more numerous, and more pronounced at the polar regions.

One thing is for sure, I'm glad our moon is out there fielding for us.

localroger

If you look at a polar projection the cratering at the poles is about the same as that across Farside. These projections just make it look worse. The difference in cratering between Nearside and Farside has to do with the Late Heavy Bombardment, the period when the planets were sweeping up the last of the debris that had coalesced to form them.

The Moon was much closer to the Earth when it formed; it has been being lifted ever higher by tidal forces (and the Earth's day getting longer, which is where the energy for the lifting comes from). When the surface of the Moon was cooling it was still close enough that the Earth's sucked up or deflected a significant amount of stuff that would have gone on to hit Nearside if the Earth hadn't been there. But Farside wasn't shielded and soaked up everything coming at it. The bombardment consisted of stuff that got smaller over time, as the big stuff was more likely to be drawn in, so the shielding had the effect of protecting the Nearside maria, which were themselves the results of very heavy early impacts, from being obscured and covered up.

If nothing interfered the tidal thing would eventually end up with the moon about 1.5x as far from us as it is, and the Earth's rotation tidally locked. However, long before that happens the Sun will become a red giant and most likely swallow both the Earth and the Moon.

Heater.

I'm trying to figure out why "picture of the day" dates from 2011 ?

Love it anyway.

Dave Hein

I think another reason the polar regions look more heavily cratered is because of the direction of the lighting. At the polar regions the sunlight is coming in almost horizontally, which produces longer shadows. I think this makes the craters stand out more in the picture. I'm not sure what the sun angle was near the equator, but the shadows are less pronounced.

As far as cratering on the near side versus the far side, it looks very similar to me in areas where the maria don't exist.

localroger

Yep Dave, now that you mention it the lighting is probably the problem with the polar regions. The farside shots were taken by robots when the farside was in direct sunlight, but that never happens with the poles.

MikeDYur

Great explanation localroger.

Another thing that is interesting about our moon is, the lack of any rotation. It would be hard to keep any small mass at one point in space, an object the size of the moon must have specific forces keeping it facing in one direction to us.

Publison

MikeDYur wrote: »

Great explanation localroger.

Another thing that is interesting about our moon is, the lack of any rotation. It would be hard to keep any small mass at one point in space, an object the size of the moon must have specific forces keeping it facing in one direction to us.

That is one thing I could never understand.

kwinn

MikeDYur wrote: »

Great explanation localroger.

Another thing that is interesting about our moon is, the lack of any rotation. It would be hard to keep any small mass at one point in space, an object the size of the moon must have specific forces keeping it facing in one direction to us.

The tidal force from earth's gravity has locked the moon's rotation to it's orbital rotation. Same is true of Mercury with respect to it's orbit around the sun. Both still rotate relative to the rest of the universe. The rotation is just locked in step with their orbital rotation period.

pmrobert

https://en.wikipedia.org/wiki/Tidal_locking is an excellent read on the subject. Pluto and Charon are tidally locked to each other! Cool stuff.

-Mike R...

Heater.

As far as I understand the "tidal locking" idea it goes like this:

1) The strength of gravity decreases with the square of distance.

2) Therefore a sizable object, planet, moon, etc orbiting something else, experiences a higher gravitational force on the side nearest its partner than the far side.

3) This force difference results in a stretching of the object. What was a sphere is not exactly a sphere anymore.

4) But as our object is rotating it is being stretched out of spherical in different directions all the time. As we see with the way the actual ocean tides rise and fall, thus making the Earth not exactly spherical in different ways everyday.

5) The resulting friction as things stretch and squeeze around sucks energy out of the rotation. Thus slowing it down.

6) Until, the object no longer rotates with respect its partner.

MikeDYur

Good stuff guy's.
In the scale the size of planets, it is a delicate balancing act.

kwinn

Heater. wrote: »

As far as I understand the "tidal locking" idea it goes like this:

1) The strength of gravity decreases with the square of distance.

2) Therefore a sizable object, planet, moon, etc orbiting something else, experiences a higher gravitational force on the side nearest its partner than the far side.

3) This force difference results in a stretching of the object. What was a sphere is not exactly a sphere anymore.

4) But as our object is rotating it is being stretched out of spherical in different directions all the time. As we see with the way the actual ocean tides rise and fall, thus making the Earth not exactly spherical in different ways everyday.

5) The resulting friction as things stretch and squeeze around sucks energy out of the rotation. Thus slowing it down.

6) Until, the object no longer rotates with respect its partner.

Exactly. Wish I could express my thoughts/knowledge as well as your explanations.

Tor

Another way of looking at what Heater describes is imagining that stretched sphere (the moon) pointing at earth, then, as the moon tries to rotate, the stretched part needs to move, like a wave, across the moon's surface, so that it still points to earth. But it resists.. it's rock and hard stuff. So the moon's rotation slows down until it's locked to its rotation around the earth, and that oblong shape never has to deform the moon to move across its surface anymore.

The closer the small sphere is to the big sphere the worse it gets, so all planets very close to their sun are quickly tidally locked, with the same side facing the sun all the time.

MikeDYur

I wonder how mankind would have evolved on earth, if this planet was tidally locked, and had one side facing the sun all of the time. We may have had that one world government to this day. It would certainly be a nightmare for tourism. Not many people want to plan a vacation to some frozen dark place where nobody else wants to be either.

We live on a well designed spaceship, with all the billions upon billions of possible places for life out there, the probability of something like we have may not exist elsewhere.

Heater.

As far as I understand, if the Earth were tidally locked there would never have been any life here. Too hot on the hot side and too cold on the cold side. And, in order to be tidally locked the Earth would be much closer to the Sun. Much, much too hot.

Sometimes I speculate that with a couple of billion stars per galaxy and a couple of billion galaxies in the observable universe, then surely there is some complex "life" out there somewhere. That's a lot of stars and a lot of planets. Some of them must work.

Other times I find myself reading about what freak situations had to happen to make it possible that we are here. It's vanishingly probable.

MikeDYur

Heater, thats another good reason to keep on Spinning.


I had tried to get a download of the image that Clock Loop had posted, so far all I can get is a screenshot 1920 x 1080. Did anyone have luck in getting better quality? Makes a nice computer background.

https://astrobites.org/wp-content/uploads/2014/06/NearAndFarMoonWiki.png


EDIT: maybe the best quality images come directly from the source:
https://www.nasa.gov/mission_pages/LRO/
main/index.html


Here is some vids to investigate:
http://lroc.sese.asu.edu/images/videos


This one is downloadable:
http://lroc.sese.asu.edu/videos/wac_moon_643nm.mp4

IMHO, AWESOME

localroger

There are actually theories that suggest a tidally locked world with an atmosphere might not be molten metal hot on nearside and liquid air on the farside, because the atmosphere would become a great big conveyor belt transporting heat from the nearside to the far. Of course you would also have the problem of the solar wind stripping away the atmosphere over geologic time (what we are pretty sure happened to Mars, which probably had a dense atmosphere and oceans billions of years ago, at least according to Curiosity). Red dwarf stars are far more numerous than stars like the Sun, and more stable, but the "goldilocks zone" where liquid water is possible is also in the "quickly tidally locked" zone near the star. It would be rather amusing to find that complex life is more common in such star systems and that the Earth and Solar System are a freakish exception.

Tor

Yeah, a slightly popular Science Fiction concept in the past (at least) was about people living at the "terminator" of such planets - that part just between the too hot day side and the too cold night side.

MikeDYur

rjo__ wrote: »

Looks like a massive asteroid embedded itself on the surface... at about 10 o'clock position.

Did you happen to notice this crater, around the 3:30 position on the backside photo. Looks like a very large very fast object caused that. Something hitting the earth on that scale could be very bad for our environment. I think we dodged a game changer.

MikeDYur

We may never know when.



"Rerun" asteroid buzzes Earth in second close shave of 2017


http://www.cbsnews.com/news/asteroid-seen-buzzing-earth-second-close-shave-of-2017/

MikeDYur

I thought this was so strange, that it could be from some other world.

Is this an alien? Probably not, but of all the animals on Earth, the tardigrade might be the best candidate. That's because tardigrades are known to be able to go for decades without food or water, to survive temperatures from near absolute zero to well above the boiling point of water, to survive pressures from near zero to well above that on ocean floors, and to survive direct exposure to dangerous radiations. The far-ranging survivability of these extremophiles was tested in 2011 outside an orbiting space shuttle. Tardigrades are so durable partly because they can repair their own DNA and reduce their body water content to a few percent. Some of these miniature water-bears almost became extraterrestrials recently when they were launched toward to the Martian moon Phobos on board the Russian mission Fobos-Grunt, but stayed terrestrial when a rocket failed and the capsule remained in Earth orbit. Tardigrades are more common than humans across most of the Earth. Pictured here in a color-enhanced electron micrograph, a millimeter-long tardigrade crawls on moss.
Image Credit & Copyright: Nicole Ottawa & Oliver Meckes / Eye of Science / Science Source Images

http://antwrp.gsfc.nasa.gov/apod/ap170326.html

Alexander (Sandy) Hapgood

Heater. wrote: »

Sometimes I speculate that with a couple of billion stars per galaxy and a couple of billion galaxies in the observable universe, then surely there is some complex "life" out there somewhere. That's a lot of stars and a lot of planets. Some of them must work.

It's possible that earth is the first instance of life. Someone has to be first.

Sandy

Heater.

True.

Given the numbers involved the odds of us being first seem pretty slim.

MikeDYur

Alexander (Sandy) Hapgood wrote: »

It's possible that earth is the first instance of life. Someone has to be first.

Sandy

Just what is our place in the universe? Are we on the outer edge somewhere, in one of the farthest galaxies from a perceived center.
If this creature was on this planet since it was formed, it would need some pretty extreme capabilities to have survived. Everything on this rock had to have those capabilities, if you weren't born with them, you evolve into something that can survive or die out like the dinosaurs.

This creature could have led to the idea behind the aerosol straw.

Heater.

There is no "center". There is no "edge".

If you listen to cosmologists they will tell you about the "Cosmological Principle". Which basically is the assumption that the universe looks pretty much the same no matter what direction you look in. And that it looks pretty much the same no mater where you are in it.

As opposed to living in some crystal lattice where different directions would look very different.

So, while it looks to us as if the "big bang" started the universe from a point. It is not so.

Why? Because if you were a being living a billion or so times further away than the size of our observable universe you would make the same observation.

And also because, if the thing started from a point somewhere then the universe would look somewhat different when we look back in the direction of that point to looking the other way to the direction we are expanding into.

My take away from all this is that the original "point" of the big bang was not a point at all. It was infinitely dense but also infinitely big. Now it is less dense but even more infinitely big.

As for those tardigrades. I was wondering....

It seems almost impossible to kill them. They can survive almost absolute zero temperature. They can survive boiling. And the huge pressure of the depths of the ocean. Or the vacuum of space. They can do without food and water for ages. They don't care about radiation.

As such, I start to think, they are at an evolutionary dead end. If they can survive anywhere, there is no pressure to evolve differently.

Clock Loop

MikeDYur wrote: »

Just what is our place in the universe?

Terence had a pretty good idea...



If you consider that the universe is not only infinitely BIG, but also infinitely small, you are left with only possibilities.


Carl, help a dude out..

MikeDYur

Clock Loop wrote: »

If you consider that the universe is not only infinitely BIG, but also infinitely small, you are left with only possibilities.


Carl, help a dude out..

Sure do miss Carl. Remember him all the way back to the Tonight Show. An extremely friendly sort of Astro Physicist who could get the point across at a basic level even a kid could understand.(which I was). The way he said "Billions and Billions" of stars, is indelible in my mind. He was a major influence in piquing my interest in space science.

https://en.m.wikipedia.org/wiki/Carl_Sagan

Thanks Heater for the spell check.

Heater.

peek, peak or pique?

https://www.vocabulary.com/articles/chooseyourwords/peak-peek-pique/