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Barnard's Star (Astrophysics)
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Hatty
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This dim star is the second closest to Sol after Alpha Centauri 3. It is located about 6.0 light-years away in the northernmost part of Constellation Ophiuchus.... the star has the largest known proper motion of all known stars (10.3 arcseconds per year). This high apparent speed is the result of its proximity to Sol as well as actual speed of travel through interstellar space. In fact, Barnard's Star is approaching Sol rapidly at 140 kilometers per second (87 miles/second) and will get as close as 3.8 light-years (ly) around 11,800 CE. Like other red dwarfs, however, it is not visible to the naked eye.


Its position has been tracked over the past 20 years, every five years, enabling astronomers to measure the speed at which it is travelling and estimate its position in 10,000 years' time.

Physicists claim it is still burning hydrogen, despite its estimated age of 11 to 12 billion years, quite a broad gap even by astrophysicists' standards. Does anyone know what a 'red dwarf' is (not the Craig Charles' version)? Its luminosity is very low but it flared up dramatically a few years ago.

A very cool and dim, main sequence red dwarf (M3.8 Ve), Barnard's Star has less than 17 percent of Sol's mass (RECONS estimate), 15 to 20 percent of its diameter

According to wiki, "were Barnard's Star to replace the Sun, it would only appear 100 times brighter than a full moon". This apparently bland statement is in fact extraordinary: where is Barnard's Star going, is it reckoned to be on a collision course with the sun?
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Brian Ambrose



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If our Sun is part of a binary pair of suns, and therefore our entire solar system is in orbit (which is the true cause of 'precession'), is it possible that Barnard's apparent speed is due largely to our own movement? That is, in 11,000 years it will be rushing away from us?
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Hatty
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Is it possible that Barnard's apparent speed is due largely to our own movement? That is, in 11,000 years it will be rushing away from us?

Barnard's speed was confirmed by measurements taken outside earth's atmosphere by Hubble.

Why would a star travelling at an incredibly fast rate towards us change direction? If its trajectory brought it close(r) to another body with a mass greater than that of the sun, the gravitational tug might deflect its course. Is there such a body?
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Mick Harper
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The phrase "Barnard's speed was confirmed by...... Hubble" is a dead giveaway that there's something of interest here to Applied Epistemologists. It's a bit like saying, "The accused's speed as registered by the speed camera was confirmed by his later statement under extreme interrogation."
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Brian Ambrose



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Barnard's speed was confirmed by measurements taken outside earth's atmosphere by Hubble

Doesn't matter. If our whole solar system is currently rushing towards Barnard, so is Hubble - Barnard's apparent speed towards us may be just our actual speed toward it.

Incidentally, if this apparent movement really is due to our orbit around a binary star, then I would expect the closing speed to vary due to the curve of the orbital path of the solar system - but it may be too fine a difference.
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Mick Harper
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Speaking of too fine a difference, if it really is "coming towards us" then I don't see why the photos should differ...which they do for five year intervals. The star background must remain the same and Barnard's Star itself merely infinitessimally bigger.

What's the red shift position when viewing very nearby stars rushing towards us? And would it be different if, pace Brian, it was us rushing towards it?

My point about Hubble, Brian, was that when viewing Barnard's Star parallax observation must be decisive. And if it isn't for our very closest neighbour what does that say about all parallax observations?
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Ishmael


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Mick Harper wrote:
My point about Hubble, Brian, was that when viewing Barnard's Star parallax observation must be decisive. And if it isn't for our very closest neighbour what does that say about all parallax observations?

Very interesting Mick. But I suspect it's more like Hubble enthusiasm on the part of scientists, Hubble-boosters, and the general public, simply seeping into an article where the subject does not belong.
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Mick Harper
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I don't think so. It may of course be that "Hubble says..." has become a kind of all-purpose truth validifier (and therefore a very interesting source of bogosity for us) but let's take it a little further, in an AE spirit.

Assuming the statement is true it must mean that at some point in Hubble's brief and very busy existence, somebody put up a proposal to use this valuable resource to measure Barnard's Star's progress. If, as one would ordinarily assume, parallax fits the bill, how was the proposal justified? "Please, Sir, we know Barnard's Star is travelling at 18.7 miles per second but we need to get it to two decimal places."

But just a mo...surely Hubble must use parallax too...or is there some other method of determining velocity that depends on particularly exact observation?
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Brian Ambrose



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I assumed that it was the frequency of the light (in this case blue-shifted) from the star which indicates its speed towards us.
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Mick Harper
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On a matter of information, is colour-shifting so accurate as to get kilometres-per-second down to a decimal place?

But now a second point which has not been raised here. What exactly does "coming towards us" actually mean. According to my sources, this means that it will 'merely' be our nearest star in about 9000 AD before 'finishing up' (huh?) in the constellation of Draco by 11000.
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Brian Ambrose



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I'd guess that 'coming towards us' is in the sense that an aeroplane is coming towards us (as we're looking up at the sky). But if they know it isn't coming directly at us, they must indeed be using some positional references as well. And yes, if it ain't coming directly at us, the background will be constantly changing.

I'm sure the accuracy of measurement of Barnard's speed from colour shift (if that is what they used) could be quite high (stated as 140km/s, dunno where you got 18.7 mps from).
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Hatty
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Maybe the view from Broadmoor is different, but most people agree its speed is 87 miles per second.

Astronomers estimate that the sun is 4.6 billion years old and will go on for another 5 billion years, yet Barnard is considered to be 11 or 12 billion years old and may continue for another 40 billion years. Where do they get these figures from?
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Mick Harper
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Not, certainly, from Harper's Constant which states that all stars last exactly the same length of time. [18.7 was a misprint. I actually use eight-seven miles per second in the DVD as a mnemonic for 186,000 miles per second.]
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DPCrisp


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Lies, damn lies and statistics.

87 miles per second is 140 kilometres per second.

140 is clearly a nominal figure. It's hard to say whether it means "closer to 140 than 130 or 150" or "closer to 140 than 139 or 141"... but for all we know it means "140 plus or minus 40" or "somewhere between 0 and 280".

87 on the other hand, creates the distinct impression that it's not 86 or 88.
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Mick Harper
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Of course it makes not a damn bit of difference so far as Barnard's Star is concerned but Dan makes a good general point. An amusing local application are road signs saying "T-junction 133 yards ahead" when clearly a metric measure had been translated.

but for all we know it means "140 plus or minus 40" or "somewhere between 0 and 280".

I'd really like to know what limits are being applied. In the video I claim that Barnards Star is due to join us in the Solar System in 12,000 years time. Obviously in the scheme of things it doesn't matter whether it's 6000 or 24,000. But now I'm told it's not going anywhere near us (except it will replace Alpha Centauri as our nearest star (does this mean a formal renaming ceremony for Alpha Centauri Proxima?) but will end up in the Polaris constellation (or something). Is this to be relied on, or is it a case of "somewhere over there". And does this include the possibility of "somewhere over here".

I ask because it appears to call Newton into question if it passes so close to us yet ends up somewhere else. What has Polaris got gravitationally-speaking that Sol hasn't?
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