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The Astronomy Thread 
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Post Re: The Astronomy Thread
Absalom wrote:
Mjolnir wrote:
As far as I'm aware, the star itself being the cause has been ruled out. A star can only change brightness by changing size (which is far too slow) or by changing temperature (which is too slow and doesn't match spectral observations). A star that rapidly dims without major changes in its spectrum is being blocked by something in front of it.
How would my flare or black hole suggestions compare?


There is a distinct maximum brightness with only minor variations, with irregular but sharply defined dips. Small stars with strong magnetic fields can be highly variable, but it's hard to see how such activity would just intermittently dim the star, and do so by such large amounts. A black hole would cause a very smooth and uniform variation, and a large amount of material orbiting the black hole would form an accretion disk with its own obvious emissions.

It seems pretty certain that this is mundane matter of some form occluding the star, it's just the specific form of that matter that is rather baffling. Too cold for a dust disk, too irregular for planets, far too much of it for it to be comets...


Tue Aug 15, 2017 8:40 pm
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Post Re: The Astronomy Thread
Mjolnir wrote:
Absalom wrote:
Mjolnir wrote:
As far as I'm aware, the star itself being the cause has been ruled out. A star can only change brightness by changing size (which is far too slow) or by changing temperature (which is too slow and doesn't match spectral observations). A star that rapidly dims without major changes in its spectrum is being blocked by something in front of it.
How would my flare or black hole suggestions compare?


There is a distinct maximum brightness with only minor variations, with irregular but sharply defined dips. Small stars with strong magnetic fields can be highly variable, but it's hard to see how such activity would just intermittently dim the star, and do so by such large amounts. A black hole would cause a very smooth and uniform variation, and a large amount of material orbiting the black hole would form an accretion disk with its own obvious emissions.

It seems pretty certain that this is mundane matter of some form occluding the star, it's just the specific form of that matter that is rather baffling. Too cold for a dust disk, too irregular for planets, far too much of it for it to be comets...
If "far too much" is the best argument against comets, then I'd say the continuum between that and your "orbital snowstorm" is the best contender... at least in this thread. Haven't looked into it elsewhere, after all.


Sat Aug 19, 2017 8:22 pm
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Post Re: The Astronomy Thread
hi hi

In other interesting news. Radio telescopes have detected a repeating Fast Radio Burst source.
Galaxy sends out 15 high energy radio bursts


Wed Aug 30, 2017 6:03 pm
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Post Re: The Astronomy Thread
hi hi

This one's been big news in the science community: Colliding Neutron Stars Detected, Support Predictions as Source of Heavy Metals


Tue Oct 17, 2017 11:05 am
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Post Re: The Astronomy Thread
Haumea appears to have a ring.


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Tue Oct 17, 2017 11:37 am
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Post Re: The Astronomy Thread
hi hi

Ross 128 has a planet in the habitable zone.

The nice thing about Ross 128 is that, while it is a red dwarf, it doesn't have all the awful flares.


Wed Nov 15, 2017 3:43 pm
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Post Re: The Astronomy Thread
The viability of habitable plants around red dwarfs is a huge question, since red dwarfs make up such a huge majority of stars in our galaxy.


Thu Nov 16, 2017 8:00 am
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Post Re: The Astronomy Thread
hi hi

Mars Reconnaissance Orbiter finds buried water ice on Mars.


Thu Jan 11, 2018 4:23 pm
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Post Re: The Astronomy Thread
This isn't new, but I found it interesting. Kip Thorne and the scientific team who worked on the black hole visualization for the movie Interstellar published a paper describing how they came up with it.

http://iopscience.iop.org/article/10.10 ... 2/6/065001

The summary of the paper is this: the visualization of the black hole "Gargantua" in Interstellar is about as accurate as modern theory allows, with one exception: the spin of the black hole would produce noticeable doppler color shift and brightness difference between the left and right sides of the disc (as one is moving at a very high velocity towards the observer, and the other away), which director Nolan thought would be confusing to the viewer. A more accurate version would look something like this:

Image

The top curve over the black hole is the top of the accretion disk (on the far side from the viewer) warped around the event horizon; the small lower curve is the bottom of the disc from the far side warped around it.

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Thu Jan 11, 2018 7:43 pm
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Post Re: The Astronomy Thread
Ahoy, this is an old thing but it's very cool. The Curiosity probe took a bunch of hi-res photos on its way down to the planet Mars. Some unsung genius took them and merged them into a video.



Thu Feb 08, 2018 11:04 am
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Post Re: The Astronomy Thread
hi hi

Here's an interesting one for all the futurists out there: Subglacial liquid water detected on Mars via radar


Wed Jul 25, 2018 9:37 am
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Post Re: The Astronomy Thread
An excellent visualization of the various meteor showers, clearly showing how each is debris from a spent comet:

https://www.meteorshowers.org/view/all

Select individual groups to more clearly view each orbit.

It's also just a nice demonstration of the orientation of our solar system relative to the galaxy: the plane of our solar system is tilted almost 90 degrees on an axis pointed almost directly at the center of the galaxy.

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Wed Aug 08, 2018 12:40 pm
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Post Re: The Astronomy Thread
Arioch wrote:
An excellent visualization of the various meteor showers, clearly showing how each is debris from a spent comet:

https://www.meteorshowers.org/view/all

Select individual groups to more clearly view each orbit.

It's also just a nice demonstration of the orientation of our solar system relative to the galaxy: the plane of our solar system is tilted almost 90 degrees on an axis pointed almost directly at the center of the galaxy.


I thought it was 60 degrees or so, so I looked around a bit and found this among some other sites that described the same or similar.

https://www.physicsforums.com/threads/o ... ay.888643/

But in any case, that's an awesome simulator, Arioch. Thanks for posting it.

CJSF


Wed Aug 08, 2018 2:16 pm
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Post Re: The Astronomy Thread
Last month this South African MeerKAT radio telescope image was released. It shows our galaxy’s central region at ~26,000 lightyears. MeerKAT will be part of a larger international Square Kilometre Array (SKA) in the Karoo (“thirsty land”) region of Northern Cape province.

Image

The bright x-ray feature in the middle outshines Sagittarius A*, which can only be imaged in the radio spectrum. The core region is a kind of gateway to hell: it packs a supermassive black hole with over 4 million times more mass than the sun, which is itself orbited by at least one other black hole with ~1300 solar masses.

http://www.ska.ac.za/media-releases/mee ... milky-way/


Sun Aug 12, 2018 12:45 pm
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Post Re: The Astronomy Thread
Those "radio filament" structures are very curious, especially that they are nearly all oriented vertically, from galactic north to south.

Sagittarius A* is theorized to have potentially thousands of black holes within about a parsec of it, as a sort of hellish black hole Oort Cloud. At least a dozen of these have been recently identified by a Chandra X-Ray survey.

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