That is, the positions and brightnesses of stars as seen from viewpoints other than our own. We found, for instance, that though the southerly star Alpha Centauri is our neighbor it sees our Sun as less bright than several others.
I’ve now managed to torture my already tortuous program for charting the stars into showing allocentric positions.
Here are the two halves of the celestial sphere, oriented in our normal way, with north at the top.
A small selection of stars is shown: to apparent magnitude 1.6 (as seen by us). They are plotted not only in the positions that we see (white) but also (orange) in their positions, and with their brightness, as seen from our nearest star, Proxima Centauri.
These two positions – heliocentric and allocentric – differ very little for very distant stars. The orange symbol for the remote supergiant Deneb is exactly hidden under the white symbol.
The difference is great for stars near to the allocenter (Proxima). For us, the Alpha Centauri A and B binary pair is deep south, at declination -62°; but for Proxima it is in the northern hemisphere.
The Sun appears as a second-magnitude star, 62° north in the sky (since Proxima is 62° south in our sky).
I am assuming (for ease of description) that our viewpoint is a planet of Proxima that happens to have a spin axis exactly parallel to that of Earth, so that “north” and “declination” mean the same for Proximans as they do for Earthlings.
Moreover, Proximans draw the same constellation boundaries on the sky as we do, even though their bright stars are in different positions! I’ve marked the boundaries of three constellations: Canis Minor, Canis Major, and Centaurus.
Sirius and Procyon are among the near stars for Proxima as they are for us, so their Proxima-centric positions jump quite widely. In fact Procyon is no longer within the boundary of constellation Canis Minor. Sirius has jumped even father north, out of Canis Major – and is, from Proxima, almost in line with distant Betelgeuse.
For not-so-near stars, such as Arcturus or Regulus, the two positions are a few degrees apaart.
It’s like parallax, the technique by which stars’ distances from us are calculated. Holding a finger up before you, you see it in different directions from your two eyes, the displacement greater if it is nearer to you. Indeed the difference between heliocentric and allocentric positions is parallax on a vast scale. It’s like those pictures in which the images from two positions are printed in red and green so that, looking through special spectacles, you see three dimensions. You have one eye here in the solar system and the other eye four light-years away at Proxima Centauri, so that looking at Altair, Vega, and Deneb you sense the steps of distance.
Supergiants get super-headaches.
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As Mr Spock 🖖 might raise his eyebrow “most fascinating!”I like to see what the lowest stars I can see from my latitude which worked fairly well from my previous home as the southern horizon was quite dark but from here and now there’s various big towns and chemical plants to my south.
This is fascinating. Thanks Guy for the concept.
This is fascinating! Thank you.
Spectacular, Guy!
Wow. Those Proximans have an incredible permanent conjunction on their celestial equator – Sirius and Betelgeuse.
I wonder what they call it.
Cat’s Eyes?
Or what passes for a cat on Proxima!
Allocentrics…..wow I just learned a new term! How I would love to verify your article by taking a trip to Proxima Centauri and looking up at our sun and other stars in the night sky. I love this stuff you write, Guy! Keep it coming, it is all great food for our star-loving community!
Thanks very much for this exercise; it adds a new dimension to Mark Haney’s CircumSpace (from 30 years ago?). btw, the concept of allocentric contemplation is one that I try to apply to matters here on earth – especially amongst humans. I do not like to express opinions until I at least understand positions other than my own – to have seen how they are valid from another perspective (temporally, culturally, politically). Makes for small company though.
I think the meaning of “allocentric” in psychology may be taking more interest in others than in oneself, whereas empathy – which I think you are describing – is understanding things from other people’s point of view.