Posted on 10/15/2018 9:07:07 AM PDT by ETL
Lol! Good one!
I guess the same goes for seeing “double stars”!
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In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes.
This occurs because the pair either forms a binary star (i.e. a binary system of stars in mutual orbit, gravitationally bound to each other) or is an optical double, a chance line-of-sight alignment of two stars at different distances from the observer.[1][2]
Binary stars are important to stellar astronomers as knowledge of their motions allows direct calculation of stellar mass and other stellar parameters.
Since the beginning of the 1780s, both professional and amateur double star observers have telescopically measured the distances and angles between double stars to determine the relative motions of the pairs.[3]
If the relative motion of a pair determines a curved arc of an orbit, or if the relative motion is small compared to the common proper motion of both stars, it may be concluded that the pair is in mutual orbit as a binary star.
Otherwise, the pair is optical.[2] Multiple stars are also studied in this way, although the dynamics of multiple stellar systems are more complex than those of binary stars.
The following are three types of paired stars:
Optical doubles are unrelated stars that appear close together through chance alignment with Earth.
Visual binaries are gravitationally-bound stars that are separately visible with a telescope.
Non-visual binaries are 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).
Improvements in telescopes can shift previously non-visual binaries into visual binaries, as happened with Polaris A in 2006.[4] It is only the inability to telescopically observe two separate stars that distinguish non-visual and visual binaries.
??? By that are you implying that they will move away beyond our ability to detect them? Its just a matter of integrating light over longer exposure time to reach further.
Just like a black hole has an event horizon, beyond which no light can return to the outside universe, so the universe has an expansion horizon beyond which any galaxy slipping over the edge becomes invisible.
Alien intelligences that don’t develop until the distant future, will see a single galaxy (or cluster of galaxies) and nothing more. They will know nothing of an expanding universe or a big bang.
https://www.space.com/11380-big-bang-evidence-universe-trillion-years.html
All theoretical. If the expanding universe ever starts to contract on itself as one theory goes then there really is no horizon, One just has to be able to see as far as time since the big bang has allowed. I only took a single graduate class in cosmology physics and that was a long time ago, but I don’t think the gravity well of a black hole is a proper analogy to the ‘edge’ of the expanding universe, if one subscribes to the big bang that is.
Contraction is off the table. Dark energy is confirmed. The expansion is accelerated and only an act of god can stop it now.
Maybe, I have not heard but I don't track things in this area like I once did. Theories change as we learn more. Yesterday the universe was an expanding spring, someday to collapse. Today it expands forever. Tomorrow who knows. I think I will be gone before the final answer is found.
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