APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
Re: APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
I suppose the list of brightest stars is based on what is resolvable by the unaided eye. So, Alpha Cen is considered brighter than Arcturus.
Re: APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
True dat, Chris, but I worked out the space dust erosion factor years ago. Briefly, the craft's outermost skin would be made of regenerative ice. With erosion recovery, filtration & re-application, a closed system reducing initial load needs, possibly even bolstered by living payload energy emissions would be possible.Chris Peterson wrote:It would probably be beyond our current capability. It would not be small, and it would cost more than any other public project ever funded. We don't know how to shield a craft at 0.1c from the kinetic impact of space dust. We don't even know how to make electronics that can reliably survive for 100 years (solid state chips grow internal shorts and fail in decades).rstevenson wrote:With our current knowledge we just might be able to make a small vehicle that could reach something like 10% of the speed of light over that sort of distance, and assuming constant acceleration and no braking at the other end (kind of like the recent Pluto mission), that makes for an average speed of 5%, or 1/20th of light speed. So for such a vehicle to reach Proxima Centauri, at 4.24 ly distance, it would take about 20 x 4.24 = 84.8 years. It would then take a further 4.24 years for the pictures to get back here, for a total of about 89 years from launch. Note that the above is wildly optimistic. Although the theory of how such a ship would operate is understood, no one has ever tried to build one.
Realistically, this is beyond our means.
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Re: APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
The explanation referred specifically to “the brightest star in the Alpha Centauri system.”Nitpicker wrote:I suppose the list of brightest stars is based on what is resolvable by the unaided eye. So, Alpha Cen is considered brighter than Arcturus.
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Re: APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
Cousin Ricky wrote:The explanation referred specifically to “the brightest star in the Alpha Centauri system.”Nitpicker wrote:
I suppose the list of brightest stars is based on what is resolvable by the unaided eye.
So, Alpha Cen is considered brighter than Arcturus.
https://en.wikipedia.org/wiki/List_of_brightest_stars wrote:
This is a list of the brightest naked eye stars, as determined by their maximum, total or combined apparent visual magnitudes as seen from Earth. Although several of the brightest stars are also known close binary or multiple star systems, they do appear to the naked eye as single stars.
*The name Regor ("Roger" spelled in reverse) was invented as a practical joke by the Apollo 1 astronaut Gus Grissom for his fellow astronaut Roger Chaffee.Code: Select all
Bayer Proper name V Mag.class ------------------------------------------------------------------ α CMa Sirius −1.46 α Car Canopus −0.74 α Cen AB Rigil Kent −0.27 : (0.01 [+] 1.33) α Boo Arcturus −0.05 α Lyr Vega 0.03 ............................................................ ε Ori Alnilam 1.69 γ Vel Suhail, Regor* 1.72 : (1.84 [+] 4.27) α Gru Alnair 1.74 ε UMa Alioth 1.77 ζ Ori Alnitak 1.77 α UMa Dubhe 1.79 α Per Mirfak 1.80 δ CMa Wezen 1.82 θ Sco Sargas 1.84
https://en.wikipedia.org/wiki/Double_star wrote:
<<In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope.
There are three types of paired stars:
Conceptually, there is no difference between the latter two categories, and improvements in telescopes can shift previously non-visual binaries into the visual class, as happened with Polaris in 2006. Thus it is only the inability to observe the third group telescopically that makes the difference.
- optical doubles—unrelated stars that appear close together through chance alignment with Earth
visual binaries—gravitationally-bound stars that are separately visible with a telescope
non-visual binaries—stars whose binary status was deduced through more esoteric means such as occultation (eclipsing binaries), spectroscopy (spectroscopic binaries), or anomalies in proper motion (astrometric binaries).
Art Neuendorffer
Re: APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
Good point, Ron!Ron-Astro Pharmacist wrote:If a star gives good evidence for close-up investigation, journeying there will need to be planned exquisitely with respect to where it will be. (As Art pointed out)![]()
Michael J. Fox, if you had a time machine that sent you back in time without sending you to the exact right point in space in the direction of Carina quite far away from "here", you would end up in empty space and freeze all the body parts off your body.
Ann
Last edited by Ann on Wed Jan 20, 2016 1:11 am, edited 1 time in total.
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Re: APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
Ann wrote:Good point, Ron!Ron-Astro Pharmacist wrote:If a star gives good evidence for close-up investigation, journeying there will need to be planned exquisitely with respect to where it will be. (As Art pointed out)
Michael J. Fox, if you had a time machine that sent you back in time without sending you to the exact right point in space in the direction of Carina quite far away from "here", you would end up in empty space and freeze all the body parts off your body.
Ann
![Freezing Cold :brr:](./images/smilies/asterisk_brr.gif)
![Freezing Cold :brr:](./images/smilies/asterisk_brr.gif)
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Re: APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
Well, yes and no ... the explanation is perhaps not worded as well as it could be:Cousin Ricky wrote:The explanation referred specifically to “the brightest star in the Alpha Centauri system.”Nitpicker wrote:I suppose the list of brightest stars is based on what is resolvable by the unaided eye. So, Alpha Cen is considered brighter than Arcturus.
Alpha Cen AB was first observed as a binary in 1689 (obviously well into the period of recorded history). So, while it is true that Alpha Cen A is similar to our Sun, it is Alpha Cen AB (considered as single source) that has been known since pre-historic times, and which is considered to be the third brightest star in the night sky.APOD Robot wrote:The brightest star in the Alpha Centauri system is quite similar to our Sun, has been known as long as recorded history, and is the third brightest star in the night sky.
Re: APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
Actually, I think that Proxima Centauri really is quite faint even as M-type dwarfs go. According to this page, the average mass of M-type dwarfs is 0.3 solar masses. But according to Wikipedia, the mass of Proxima Centauri is only 0.123 ± 0.006 solar masses. Mass is strongly correlated with luminosity in main sequence stars, like the Sun and Proxima, so that the more massive a star is, the brighter it is. Correspondingly, the less massive the star is, the fainter it is.jisles wrote:Pace today's APOD, Proxima Centauri is not unusually faint. Its apparent magnitude is 11 and it can be seen in a small telescope. What was discovered in 1915 was its closeness to us rather than its existence.
John
So we have reason to think that Proxima might be on the faint side even for red dwarf stars. It is reasonably bright to us - magnitude 11 - only because it is so close to us. Its absolute magnitude is 15.4, which is really quite faint.
Ann
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Re: APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
And John clearly was talking about its reasonably bright apparent magnitude of 11 (and not its absolute magnitude of 15.4). What is not clear, however, is whether the APOD explanation was, in fact, referring to its dim absolute magnitude... in which case John probably doesn't have much of an argument.Ann wrote:It is reasonably bright to us - magnitude 11 - only because it is so close to us. Its absolute magnitude is 15.4, which is really quite faint.jisles wrote:
Pace today's APOD, Proxima Centauri is not unusually faint. Its apparent magnitude is 11 and it can be seen in a small telescope. What was discovered in 1915 was its closeness to us rather than its existence.
Art Neuendorffer
Re: APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
Good point, Art. John, I wasn't trying to criticize your observation that Proxima is well visible in many amateur telescopes.And John clearly was talking about its reasonably bright apparent magnitude of 11 (and not its absolute magnitude of 15.4).
But I do find it fascinating that the nearest star outside our solar system really is so faint, even as small red dwarfs go. It is of course another fascinating coincidence that the brightest component of the Alpha Centauri system really is so Sun-like. Stars like the Sun actually aren't all that common. When Wikipedia lists the nearest 56 stars and brown dwarfs, there are only two early G-type stars among them. One is the Sun, the other is Alpha Centauri Aa.
Ann
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Re: APOD: Proxima Centauri: The Closest Star (2016 Jan 18)
APOD Robot wrote:Proxima Centauri: The Closest Star
Explanation: Does the closest star to our Sun have planets?
https://en.wikipedia.org/wiki/Unobtainium wrote:
Unobtanium
<<James Cameron's Avatar is set in the mid-22nd century, when humans are colonizing Pandora, a lush habitable moon of a gas giant in the Alpha Centauri star system, in order to mine the mineral unobtanium, a room-temperature superconductor. Unobtainium is any fictional, extremely rare, costly, or impossible material, or (less commonly) device needed to fulfill a given design for a given application. The properties of any particular unobtainium depend on the intended use. For example, a pulley made of unobtainium might be massless and frictionless; however, if used in a nuclear rocket, unobtainium would be light, strong at high temperatures, and resistant to radiation damage. The concept of unobtainium is often applied flippantly or humorously. For instance, unobtainium is described as being stronger than helium, and lighter than air.>>
https://en.wikipedia.org/wiki/Upsidaisium_%28story_arc%29 wrote: Upsidaisium
<<Bullwinkle receives a letter informing him that his uncle Dewlap has passed on, leaving him a mine located on Mt. Flatten. Captain Peter "Wrong Way" Peachfuzz has been sent to make sure Rocky and Bullwinkle find Mt. Flatten, as its ore, the anti-gravity metal Upsidaisium, is much sought after by the U.S. government. While under the guise of a pair of prospectors, Boris and Natasha manage to help Rocky and Bullwinkle locate Mt. Flatten, which floats high in the air due to the high amount of Upsidaisium within it. Once they reach the mountain, Boris and Natasha are joined by their intimidating superior, Mr. Big, who tells them that Pottsylvania also seeks Upsidaisium as a means to eliminate a traffic problem (by building cars with the anti-gravity ore). Eventually, thanks to Rocky's ingenuity, Mt. Flatten is transported to Washington D.C., and the Upsidaisium is put under lock and key by the government.>>
https://en.wikipedia.org/wiki/Ununpentium wrote:Ununpentium: Uup
<<Ununpentium (Uup) is the name of a synthetic superheavy element in the periodic table that has the atomic number 115. Ununpentium is calculated to have some similar properties to its lighter homologues, nitrogen, phosphorus, arsenic, antimony, and bismuth.
Ununpentium is expected to be in the middle of an island of stability centered around copernicium (element 112) and flerovium (element 114): the reasons for the presence of this island are however still not well understood. Due to the expected high fission barriers, any nucleus within this island of stability exclusively decays by alpha decay and perhaps some electron capture and beta decay. Although the known isotopes of ununpentium do not actually have enough neutrons to be on the island of stability, they can be seen to approach the island as in general, the heavier isotopes are the longer-lived ones. Its most stable known isotope, 289Uup, has a half-life of 220 milliseconds.>>
Art Neuendorffer