News Briefs: Astronomy, Astophysics & Space Exploration

A well known polymath whose published works range far and wide, including (but not limited to) Archaeology, Paleontology, Astronomy, Space Propulsion systems, and Science Fiction.

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Voyager 2 discovers solar system is bent

Postby Paladin » Tue Dec 11, 2007 12:29 pm

Voyager 2 discovers solar system is bent

http://www.cnn.com/2007/TECH/space/12/1 ... index.html
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Postby Mr. Titanic » Wed Dec 12, 2007 12:47 pm

Well, not the solar system itself (the planets and asteroid belt etc) but the Sun's influence, right? The Voyagers are past even Pluto now, so surely they mean radiation from the sun as opposed to the planets orbiting on a bent axis?
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Postby wolfspirit » Wed Dec 12, 2007 2:16 pm

Physics 225 Final - Scott Morschbacher
Problem 8:
If an Earth-hating deviant were to somehow suddenly stop Earth in its orbit, how long would real Earth-lovers (as opposed to the fake Earth lovers(Al Gore)) have to figure out a way to stop the Earth from reaching its fiery demise on the surface of the Sun? Express your answer in days. The radius of Earth's orbit is 1.498 x 10^8 km, the radius of the Sun is 6.96 x 10^8 m, and the mass of the Sun is 1.98 x 10^30 kg. How fast would it be moving when it arrived, assuming it was not burnt up along on the way? Burnt up by the Sun, that is; not by global warming.


For some amusement, this is one of the questions from my final exam this semester (note, this problem is stupid easy, but amusing).

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Postby Darb » Wed Dec 12, 2007 3:15 pm

Trick question. The earth lovers would have ZERO TIME to find a solution, because instantaneously stopping the Earth's orbital motion (i.e., sudden deceleration from Mach 90 to zero) would cause such incredible g-forces that it'd shatter the planet, and destroy all life ... and the sudden gravimetric disruption would likely cause massive quakes on the moon as well, which would go shooting off on it's own, at an angle dependant on it's orbital position relative to the Earth (and if it were trailing us, it might even run into us, like a giant lunar enema).

If you really want to do some mathematical marturbation, you could figure out the disruption to the sun's motion (relative to both the solar system center and to the center of the galaxy) caused by the Earth suddenly slamming to a halt, like a dog hitting the end of it's chain. ;)
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Postby voralfred » Wed Dec 12, 2007 4:02 pm

Brad is right, of course.
However, taking the question at face value, to find how long they have, you don't need the radius of the sun, nor its mass, nor the radius of the Earth orbit.
All you need is the length of the year, and Kepler's third law.
For a circular trajectory, of great axis twice the Earth-Sun distance, the period is one year.
The trajectory considered is a "collapsed" ellipse, the great axis is just once the Earth-Sun distance, thus half that of the present orbit. The full period would this be one year of 365 days divided by 2 square root of 2, or about 130 days. But the Earth hits the Sun in half a period, thus 65 days.
This is the time to hit the Sun if it were of zero radius. However the Sun's radius is very small compared to the Earth-Sun distance and morover by that time the Earth is at its fastest so yu can ignore that correction.

Edit:
On the other hand, you do need all these data to know how fast it would move upon impact. Only the time to reach the Sun is easy to compute. I did not read carefully the full question before posting, just the first line
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Postby Darb » Fri Dec 14, 2007 3:33 pm

I missed the meteor display ... it was overcast early in the evening, and after 3 consecutive nights of little or no sleep, I finally managed to crash for a good 6 hrs last night.
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Postby Charlie P. » Sun Apr 13, 2008 3:00 pm

I still fail to understand why there is so much interest in a return to the moon, rather than to one of the smaller (two football field diameter) Earth co-orbital asteroids. They're usually only three or four times farther away, require a simple mission involving a mere docking - and when you get there, and look at the horizon, you'll really know you've gone somewhere new: Earth and moon are together in the sky. To say nothing of the practicality of continuing to learn what asteroids and comets are made of.

The smaller, office block sized pieces of solar driftwood are the most common ones that approach us - and they can certainly bring the sorts of meteor showers no one in his or her right mind really wants to see.

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Postby voralfred » Sun Apr 13, 2008 5:43 pm

Charlie P. wrote:...Earth co-orbital asteroids. They're usually only three or four times farther away



I am not sure what you mean here.
Earth co-orbital asteroids in horseshoe orbit spend a large fraction of their time at distance from Earth of the order of the Earth-Sun distance (between twice that distance and, say, half of it, or 700 to 200 Moon-Earth distance). Of course, they spend some amount of time closer than that, but the closest approach, as far as I found out on the web, looks like of the order of tens of Moon-Earth distances, rather than three or four, and anyway that is for only a small fraction of their trajectory. Which asteroid did you mean, exactly? 2002 AA29? It has already left its closest approach of 2003, and will be getting farther and farther for the next 50 years or so. Granted, occasionally it goes from a horseshoe orbit to a quasi-satellite one, but that won't happen before 2600 or so...
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Postby tollbaby » Sun Apr 13, 2008 11:39 pm

Last edited by tollbaby on Mon Apr 14, 2008 1:40 pm, edited 1 time in total.
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Postby voralfred » Mon Apr 14, 2008 1:05 am

According to that article, 2003 YH107 was indeed in quasi-satellite orbit ("corkscew") between 1996 and 2006 but has gone back to horseshoe about two years ago. By the time we do anything about it it will be rather far. Granted, it'll come back in about 60 years, but neither of us is likely to be around then... well, you, maybe, but possibly not in good enough condition to be interested in what's happening on an asteroid...
2004 GU9 is more interesting, as its corkscrew orbit has lasted for centuries and is likely to stay so for some time. But its closest approach, according to
http://www.space-mining.com/2004GU9.html is .17 AU or more than sixty Moon-Earth distance.
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Postby Charlie P. » Mon Apr 14, 2008 10:08 am

There are a few tiny ones that come close - and it is possible to believe that we have a chance about every decade or so (as more are charted). Even outward between 4 and ten Earth-moon diameters, with the rockets currently available, the travel time can be kept down to about 20 days, each way. It certainly beats the current Mars plan - and would be orders of magnitude less expensive than building a new, three-crew member Lunar Module (which just strikes me as being analogous to saying that, 4 decades after Kittyhawk, you someone was planning to build the Wright Brothers' plane bigger, to carry three people - and to carry them twice as far - when they're already entering the jet age).

Now, Titan has methane-ethane rivers, lakes, air pressure negating the need for pressure suits (50% greater than sea-level air on Earth), plenty of water-ice, oceans under the ice (the volcanoes are erupting water), and unlike Mars, the radiation environment does not make the most nuclear devastated Earth we can create look like a church picnic by comparison. With the propulsion systems we should have on hand in 40 years (Vasmir Marc III, Valkyrie Marc 1), we can actually carry on with a smaller version of the Oregon Trail to Titan, with inflatable habitats and travel times of less than two months. (And when all is said and done, for those of us who tune in to the Mars Rovers every morning, the one thing I am learning is that martian landscapes are - well... boring. I wouldn't want to live there and even Phobos seems infinitely more interesting - so, I'd be content to just keep sending robots and wait for better rockets that don't require more than six months of travel time, each way)

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Postby Echus Cthulhu Mythos » Fri Jun 27, 2008 12:16 am

The penis mighter than the sword.
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Postby Mr. Titanic » Fri Jun 27, 2008 11:30 pm



Fascinating! I'll be sure to mention that in my class starting Monday concerning the possibility of life in the universe beyond of Earth.
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Titan for the weekend?

Postby qraal » Thu Jan 01, 2009 5:31 pm

Hi Charlie

Titan definitely has a lot of pluses but 1.4 billion kilometres is a long way even with a 1 gee drive - 9 days one-way. Of course I'd be happy with a couple of month journey time. Even a couple of years! Ultimately we want wormhole shortcuts to all the planets, so transit times are no longer than trips on Earth.

Charlie P. wrote:Now, Titan has methane-ethane rivers, lakes, air pressure negating the need for pressure suits (50% greater than sea-level air on Earth), plenty of water-ice, oceans under the ice (the volcanoes are erupting water), and unlike Mars, the radiation environment does not make the most nuclear devastated Earth we can create look like a church picnic by comparison.


Amazes me how many people think Titan has a radiation problem because it doesn't have a magnetic field. With 10 times Earth's column mass overhead? Don't be daft! Mars is definitely nastier by comparison. However will there be enough radiation? We need some background rads to maintain health, as studies on radiation hormesis have shown.

With the propulsion systems we should have on hand in 40 years (Vasmir Marc III, Valkyrie Marc 1), we can actually carry on with a smaller version of the Oregon Trail to Titan, with inflatable habitats and travel times of less than two months. (And when all is said and done, for those of us who tune in to the Mars Rovers every morning, the one thing I am learning is that martian landscapes are - well... boring. I wouldn't want to live there and even Phobos seems infinitely more interesting - so, I'd be content to just keep sending robots and wait for better rockets that don't require more than six months of travel time, each way)


One 'cool' idea IMHO is that settlers tap into the liquid water in fresh craters and use it to warm their habitats. Or even piping water from cryovolcanic outflows. Throw in a couple of additives and you can turn it into structures - fill up a double-walled inflatable with the stuff.

Bussard fusors would be a good low mass way to power a souped up VASIMR for the long haul to Titan. Otherwise we'll need gas-core reactors with MHD converters to do the job.
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Re: News Briefs: Astronomy, Astophysics & Space Exploration

Postby Darb » Sun Jan 10, 2010 9:11 am

Have people been keeping up with Cassini ?

Sample
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Re: News Briefs: Astronomy, Astophysics & Space Exploration

Postby voralfred » Sun Jan 10, 2010 1:24 pm

:clap: :clap: :clap:
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Re: News Briefs: Astronomy, Astophysics & Space Exploration

Postby Darb » Tue Jan 12, 2010 4:06 pm

Refurbished Hubble re-scans part of the Ultra Deep Field of 2004, and finds oldest galaxies yet:

http://www.nytimes.com/2010/01/12/scien ... y.html?hpw
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Re: News Briefs: Astronomy, Astophysics & Space Exploration

Postby Darb » Sat Jan 16, 2010 11:09 am

I'm sure some of you have already seen this elsewhere, but I figured I'd repost it here ...

Chart of comparative star sizes ...

http://kilo.nncdn.com/nn/0/162/165/353424.jpg (1.5 mb)

Very impressive ... esp (to me) "Binar Star VV Cephei". I had no idea that blue supergiants could get that big, much less be part of a binary system ... and with an expanding red supergiant no less. I'm sure there's a good chance that one of the pair has probably long since exploded (forming a black hole that subsequently devoured the companion) and that the flash simply hasn't reached us yet.
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Re: News Briefs: Astronomy, Astophysics & Space Exploration

Postby Mr. Titanic » Sat Jan 16, 2010 8:02 pm

Darb wrote:I'm sure some of you have already seen this elsewhere, but I figured I'd repost it here ...

Chart of comparative star sizes ...

http://kilo.nncdn.com/nn/0/162/165/353424.jpg (1.5 mb)

Very impressive ... esp (to me) "Binar Star VV Cephei". I had no idea that blue supergiants could get that big, much less be part of a binary system ... and with an expanding red supergiant no less. I'm sure there's a good chance that one of the pair has probably long since exploded (forming a black hole that subsequently devoured the companion) and that the flash simply hasn't reached us yet.


There is also a video for that as well, which can be found here.

I prefer the image myself, although the way that video pans out is interesting and breathtaking. A very creative effect, although I notice some exaggeration between one or the other on at least the Sun-Sirius size difference.
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Re: News Briefs: Astronomy, Astophysics & Space Exploration

Postby Charlie P. » Sun Jan 17, 2010 12:34 pm

Another ultimate argument-ender: If someone at your school or workplace develops an ego that would make any normal person's skull explode, and is making you really sick with it, just print out the above chart and ask, after a good looking-over, "Now, who do you really think you are?" - - Charlie P.
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Re: News Briefs: Astronomy, Astophysics & Space Exploration

Postby Darb » Sun Jan 17, 2010 11:20 pm

Space Shuttles for sale !

As seen on TV ... operators are standing by ... call now.

Buy within the next 3 mins and get a free Ab Lounge !
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Postby voralfred » Mon Jan 18, 2010 1:59 am

Darb wrote:(...)
Very impressive ... esp (to me) "Binar Star VV Cephei". I had no idea that blue supergiants could get that big, (...)


Indeed! They cannot! This is a mistake in the chart. Look at Wikipedia: the companion is a blue giant, sure, but a main sequence blue giant, with "barely" ten times the radius of the sun.
Were it about the same radius as the hypergiant red, or 160 times bigger, its luminosity would be about 25000 times larger than what is is, ten thousand times larger than the red supergiant (which would be invisible in the glare...) or 2.5 billions that of the sun. It would eat up one sun's mass of hydrogen per year or so, and however massive it would be (hundreds of solar masses? thousands?) its expected lifetime would be in centuries or millenia only... It would also be, by far, the brightest "point-like" object in the sky, hundreds of times brighter than even Venus or Jupiter at their brightest.
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Re: News Briefs: Astronomy, Astophysics & Space Exploration

Postby Charlie P. » Mon Jan 18, 2010 9:13 pm

Yes, there is a color error in the chart. Blue stars of several solar masses do not last very long, and can start swelling to red giantism in less than 50 million years - probably (if they start out massive enough) in as few as 50,000 years. This was part of Francis Crick's hypothesis for Prompt Initial Enrichment of the galagy with heavy elements (which he called P.I.E. in the sky). Never mind, it's a long story involving setting the specific "instant" at which it was first possible, then likely, for earth-like planets to become massive enough to hold onto their hydrogen (ie water) within a star's habitable zone. At a rough estimate, Earth and Alpha Centauri A and B seem to have formed at about the right time - near the starting line. (But Dark Energy and Dark Matter in the early, denser universe might be changing the ratios, possibly leaning toward Crick's PIE). If that's the case, we're back again to Fermi's Dilemma, because it could turn out that the rest of the galaxy had a 1byr headstart after all, for all we know. (Then again, for all we know, it's great to know that there's still so much more we don't know) - - Charlie P.
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Re: News Briefs: Astronomy, Astophysics & Space Exploration

Postby voralfred » Mon Jan 18, 2010 9:53 pm

Charlie P. wrote:Yes, there is a color error in the chart. Blue stars of several solar masses do not last very long, and can start swelling to red giantism in less than 50 million years - probably (if they start out massive enough) in as few as 50,000 years. (...)


Color error? From different sources, I found confirmation that the companion is indeed a blue giant, but an "ordinary", main sequence blue giant, with luminosity just a few times less than the hypergiant red, but a much smaller radius. So it is a radius error, rather than a color error. It will indeed swell to red giantism in a 'short' time measured in millions of years, or even less (though with all the material it is accreting from the hypergiant its evolution will probably be atypical). Since its companion has already reached the red giant stage, it must have started even heavier, and lasted even less. But if the radius of a blue star were comparable with that of the red hypergiant (1600 or so times the solar radius), it would last just a few thousand years or less.
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Re: News Briefs: Astronomy, Astophysics & Space Exploration

Postby clong » Sat Feb 13, 2010 8:18 am

Not exactly a news brief, but a very cool photo:

http://www.nasa.gov/multimedia/imagegal ... _1592.html
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