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rfmcdonaldThe most recent book put out by a certain prominent Canadian science-fiction writer ends with an entity transmitting its goodbyes from an Earth soon to be engulfed by red giant Sol five billion years in the future to Earth's nearest neighbours, Alpha Centauri and Sirius.
I'll note, briefly and firstly, that Sirius won't be around in five billion years, save as a binary pair of white dwarfs long run out of fuel--Sirius A, like white dwarf Sirius B, is much too massive to last longer than a few hundred million years. I suppose it's possible that an advanced civilization somehow altered Sirius' mass, drawing off entire solar masses worth of material via some godtech method, but this isn't supported by the text: why, if Sirius could be engineered in such a way, wasn't Sol transformed?
The more important point that needs to be made is that stars do not move at the same speed and in the same directions. Quite the contrary, as this source, incidentally concerned with Alpha Centauri, notes in its description of the movement of stars.
Wikipedia observes that Alpha Centauri possesses high proper motion relative to Sol. While the precise figures differ, the general trend remains the same.
Alpha Centauri isn’t the only star that can change place radically. The bright star Algol--now 93 light years away was as close as 9.8 light years 7.3 million years ago, while the orange dwarf Gliese 208 was calculated to have passed within five light years of Sol only a half-million years ago, but is now about 37 light years away. Barnard’s Star, too, famous for the debunked claims of a planetary system and its high velocity relative Sol, will come to a point 3.8 light years from Sol around 11700 CE before moving away. In the more distant future, meanwhile, it’s been observed that the orange-red dwarf Gliese 710--now 63 light years away--will come within 1.1 light years of Sol in less than 1.4 million years, one Russian astronomer determining that there's a very high probability that Gliese 710 will penetrate the Oort cometary cloud and toss comets about.
What does this mean for people considering our planetary system’s location relative to other stars in the past, whether in astronomy or in science fiction? It means that the distances between stars, hence the relative influences of stars upon each other, change hugely over time. Was there a compact group of stars, product of the same celestrial nursery, a billion or so years ago? Those stars will now be scattered across the galaxy. Did a past civilization establish colonies and outposts in thousands of different planetary systems even a million years ago? These planetary systems will be rather scattered, some systems that were neighbours at that civilization’s height being far separated now, some high proper motion stars escaping the sphere entirely.
In brief, over time space changes. This should never be forgotten, by anyone interested in the great beyond.
I'll note, briefly and firstly, that Sirius won't be around in five billion years, save as a binary pair of white dwarfs long run out of fuel--Sirius A, like white dwarf Sirius B, is much too massive to last longer than a few hundred million years. I suppose it's possible that an advanced civilization somehow altered Sirius' mass, drawing off entire solar masses worth of material via some godtech method, but this isn't supported by the text: why, if Sirius could be engineered in such a way, wasn't Sol transformed?
The more important point that needs to be made is that stars do not move at the same speed and in the same directions. Quite the contrary, as this source, incidentally concerned with Alpha Centauri, notes in its description of the movement of stars.
Compared with our Sun’s own motion, the distribution of stellar velocities can vary significantly. Most stars are either receding or approaching us at tens of kilometres per second. A few travel at nearly 250 kms-1, and are often referred to as high velocity stars or runaway stars. and are believed to be ejections from past violent cataclysmic events within the Milky Way. Three examples include, Mu Columbae, AE Aurigae and 53 Arietis each having velocities exceeding 200 kms-1, and whose point of origin seems to be the Great Nebula in Orion. The highest velocities are sometimes caused by stars having galactic rotations opposing the Galaxy’s clockwise motion.
Astronomers have measured such motions using transit telescopes, by measuring stellar motion across the line of sight - the common proper motion (c.p.m.) or simply proper motion. For most stars, proper motion amounts to small movements that seldom exceed 0.1 arcsec per year. Proper motion is also dependent on stellar distance. For example, the angle made by two stars that have the same velocity through space. but one being twice as far as the other, will show haft the proper motion. Another measured motion is the stellar velocity relative to the Sun - obtained using spectroscopes or spectrographs. Such instruments observe certain spectral lines produced by stellar atmospheres, whose relative motion is detected by the so-called Doppler shift - similar in principle to the radar used by the police in catching speeding motorists. Called the radial velocity, it is measured from the positional differences between spectral lines observed on Earth and from the star. A negative value indicates movement towards us, positive is movement away. Using positional data from the last two centuries with the radial velocity, the true direction of motion relative to the Sun can be determined. This true speed of motion is called the transverse velocity. Applying this to the nearby stars, it is possible to use the information to calculate the true space motion relative to the Sun and resultant changes in distance and brightness.
Average values for α Centauri AB measure -22.7 kms-1 for radial velocity and about 9’ arcsec. per year for proper motion. This information combined with the parallax from the Hipparcos satellite finds the closest approach occurring in the year 31,240±1320 AD. at 2.970’0.012 ly. from the Sun. Then it will be -1.28 magnitude. slightly fainter than Sirius. and will appear in the constellation of Hydra.
Wikipedia observes that Alpha Centauri possesses high proper motion relative to Sol. While the precise figures differ, the general trend remains the same.
Based on these observed proper motions and radial velocities, Alpha Centauri will continue to slowly brighten, passing just north of the Southern Cross or Crux, before moving northwest and up towards the celestial equator and away from the galactic plane. By about 29,700 AD, in the present-day constellation of Hydra, Alpha Centauri will be 1.00 pc or 3.26 ly away. Then it will reach the stationary radial velocity (RVel) of 0.0 km/s and the maximum apparent magnitude of −0.86V — similar to present day Canopus. Soon after this close approach, the system will begin to move away from us, showing a positive radial velocity.
Due to visual perspective, about 100,000 years from now, these stars will reach a final vanishing point and slowly disappear among the countless stars of the Milky Way. Here this once bright yellow star will fall below naked-eye visibility somewhere in the faint present day southern constellation of Telescopium. This unusual location results from Alpha Centauri's orbit around the galactic centre being highly tilted with respect to the plane of our Milky Way galaxy.
Alpha Centauri isn’t the only star that can change place radically. The bright star Algol--now 93 light years away was as close as 9.8 light years 7.3 million years ago, while the orange dwarf Gliese 208 was calculated to have passed within five light years of Sol only a half-million years ago, but is now about 37 light years away. Barnard’s Star, too, famous for the debunked claims of a planetary system and its high velocity relative Sol, will come to a point 3.8 light years from Sol around 11700 CE before moving away. In the more distant future, meanwhile, it’s been observed that the orange-red dwarf Gliese 710--now 63 light years away--will come within 1.1 light years of Sol in less than 1.4 million years, one Russian astronomer determining that there's a very high probability that Gliese 710 will penetrate the Oort cometary cloud and toss comets about.
What does this mean for people considering our planetary system’s location relative to other stars in the past, whether in astronomy or in science fiction? It means that the distances between stars, hence the relative influences of stars upon each other, change hugely over time. Was there a compact group of stars, product of the same celestrial nursery, a billion or so years ago? Those stars will now be scattered across the galaxy. Did a past civilization establish colonies and outposts in thousands of different planetary systems even a million years ago? These planetary systems will be rather scattered, some systems that were neighbours at that civilization’s height being far separated now, some high proper motion stars escaping the sphere entirely.
In brief, over time space changes. This should never be forgotten, by anyone interested in the great beyond.
