Well, 1st things 1st - Tin foil hat on:Are we overthinking the puzzle of the Rift? Obviously. Once we've cracked the Rift open and revealed its secrets most of our theories will seem silly. Until then... every theory... no matter how far fetched... is worth investigating. Think it has something to do with Alice in Wonderland? Please chase down that rabbit hole! Convinced the answer lies in Greek mythology? Investigate it and see where it leads. Believe that the answer actually lies on the opposite side of the Galaxy heading toward the galactic core? Chase that path!
We can work together trying to prove or disprove each other's theories.
That said... I'd like to introduce my own tin foil hat for the evening:
A lot of talk about the "Heart Nebula" has really got me thinking and, while I'm still out in the center of the galaxy hunting neutron stars in order to afford my rift-ready starship, I can still contribute to the conversation through researching the subject.
Several internet sources state that the Heart Nebula's color comes from an open cluster of stars called Melotte 15. What I find really interesting though is that these sources also state that, about a million years ago, this cluster contained a microquasar that has since been expelled from the cluster.
Where did this microquasar go? Can we find it in game now? I'm very, very curious about this and, while it may have absolutely nothing to do with the puzzle before us, I'm still interested in pursuing this particular lead.
IMHO, the rift is not at/in the H&S Nebula. These nebulas are located at the Perseus arm and doesn't look like a hard place to reach. While a very interesting region in the sky, I have my doubts.
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I think its either more towards 140 deg between the outer arm and the Perseus arm, out 15kly. There is a massive gap.
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If we look for an island or isolated place the spot in the outer arm, a ~140 deg would do.
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Another option is to face the core, than watch your six and one ends up with a view along 180 deg. There is a nice gap in the outer arm. Also at 120 deg, which might match with R-R line.
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To the point on the Greek mythology, I searched for tales around "rift, gap, crack, ..., sky, heaven" and the interweb came up with Khaos.
Greek χάος means "emptiness, vast void, chasm, abyss", from the verb χαίνω, "gape, be wide open, etc.", from Proto-Indo-European *ǵ[SIZE=2]h[/SIZE]eh[SUB]2[/SUB]n,[URL="https://en.wikipedia.org/wiki/Chaos_(cosmogony)#cite_note-2"][SIZE=2][2][/SIZE][/URL] cognate to Old English geanian, "to gape", whence English yawn.[URL="https://en.wikipedia.org/wiki/Chaos_(cosmogony)#cite_note-OnEtD-3"][SIZE=2][3][/SIZE][/URL] It may also mean space, the expanse of air, and the nether abyss, infinite darkness.[URL="https://en.wikipedia.org/wiki/Chaos_(cosmogony)#cite_note-chaos-4"][SIZE=2][4][/SIZE][/URL] (Wikipedia)
No location is linked to this dude
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Tin foil hat off.

galaxy.org
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ps: maybe its this ... and we shouldn't look?
[video=youtube;M7YKWmPV-8c]https://www.youtube.com/watch?v=M7YKWmPV-8c[/video]