Reddit user sigbjoernwilderness's idea is pretty wild... can it be easily ruled out?
> Is this the last remaining explanation after Montet/Simon?
> The dimming comes from the shadow of a spaceship traveling on an (almost) straight line from KIC8462852 to Earth. The slow continuous dimming results from the increase of the apparent size of the approaching ship while Earth/Kepler is in the penumbra. The irregular dips happen when Kepler accidentally passes the antumbra. A rough estimation by simple geometry would suggest that the alien spaceship is quite big (> 100 km diameter), significantly slower than light velocity (< 0.05 c) and has now almost reached its goal (< 2 ly away), arriving at Earth within the next 100 years after a journey of several 10,000 years. (cf. http://archimedes.soup.io/post/632873371/) The c200 days of "rapid decreased flux" between Kepler-day 1100 and 1300 (first half of 2012) which Monet/Simon reported, followed by a series of large dips after day 1500, would suggest a course correction with the space ship now on its final homing trajectory. -- Comments?
Yes: parallax breaks it. If something's colinear with a star today (and occults it), it won't be colinear 6 months later, when the Earth's on the other side of the sun.
At 2 light years for instance, that spacecraft would trace an apparent ellipse 3.3" in diameter, while Tabby's star (1,480 ly) would be stationary (0.004" parallax). In comparison, the star's apparent disk is just 30 μas wide (0.00003").
If I'm doing that math right, it works out that to not be ruled out by parallax, the object would have to be almost 2 AU in diameter if it was within a few light years of Earth. That seems pretty ridiculous--now we have them not only building a megastructure, but flying it to Earth!
However, I wonder if there is a way to save the idea without requiring a ridiculously large spacecraft? Suppose instead of one ginormous ship, it is a fleet of big ships each big enough to cause irregular dimming if that ship happens to get between Earth and KIC8462852. If the fleet is spread out, it could then be that one ship or another ends up between Earth and KIC8462852 at several times during one Earth orbit around the Sun.
That would give us the irregular dimming throughout the year.
For the slow continuous dimming, perhaps that is something going on with the star itself. That could be what made the inhabitants of the system decide to build a fleet of big ships and leave their weirdly behaving and very scary star.
Maybe the visible size of the ship is bigger, as it's unfolding / building a solar sail to brake using our sun's radiation? (like a parachute on a drag racer). Ah, but 2au is probably still way too big?
There's a comment [1] in the other reddit thread that somewhat rules this out.
> That doesn't even make sense when you're flying within the Solar System. Stuff moves, so you have to fly towards where it's going to be, not where it is.
> The star is far enough away to be treated as a point source, with its light forming an apparent cone with the Earth's diameter. It doesn't intuitively make sense, at least to me, that the ship would stay within that cone as it corrects for the motion of our Solar System (and its own) within our galaxy. Remember that this dimming effect has been observable for several decades.
Then again, aliens don't have any obligation to make sense to us.
A while back I had a plan for a science fiction setting: an intergalactic ship is approach Earth. The people who sent it thought big, and as a result the ship has at its core an enclosed star (a miniature Dyson Sphere) as a gravitational anchor and power source, and round it is orbiting a vast swarm of asteroids and habitats with a few million times the living space of Earth, inside which civilisations endlessly rise and fall.
The plot centred around this thing going to make a class pass by Sol in a few years at 0.01c, with the gravitational effects pretty much dooming the Earth; so the current lead civilisation sends some ships on ahead to evacuate the Earth. (Big ships. I did the maths.)
The story never gelled, but I think it's plausible that my ship would produce these effects.
Terre en fuite (Fleeing Earth) (1960) by François Bordes (pen name Francis Carsac), though, there is still no translation in english of that gem, where Earth and Venus was converted to spaceships for running away from exploding Sun!
Unless military tactics dictate that they try to "hide" in the cone since they first picked up our radio signals... Even If they're on a "civilian" mission, they might have navigators/a captain with military training...
a) Tabby's Star is roughly 1500 light years away from us; we only began emitting radio signals ~150 years ago (at most -- assuming propagation from early telegraph wires; not actually very likely) and it'd take ~3000 years for our signals to reach the vicinity of Tabby's Star and indications of a reaction getting back to us,
b) "Military" is a category error on this scale; the energy budget required to generate the sort of luminosity changes we're seeing around Tabby's Star by deliberately occulting it are mind-blowing compared to anything we've ever achieved. Might as well speculate about an ant-hill (us) wondering about the military intentions of an M1 Abrams tank driving across the Iraqi desert (hypothetical alien actors at Tabby's star) -- either they aren't going to drive over us, or we just encountered an Outside Context Problem.
Do spaceships travel in a straight line? I thought their trajectories are heavily curved in really weird ways due to the garvities of stars and planets around them. Please enlighten me!
It depends on the frame of reference, which can be somewhat arbitrary.
A ship can sail a straight line from Falmouth to Boston, but that motion can be described as an arc because of the curvature of the Earth. Add in the motion of Earth's orbit, and the shape of that motion changes again. Add in the Solar System's motion relative to the Galactic Centre, and it's yet another shape.
The straight line from Falmouth to Boston is only straight on a 2d map, because of particular transformation from 3d surface to 2d plane. Nothing to do with reference frame.
You indeed can change a curve into a straight line by manipulating the frame of reference, but it would need to be very contrived - basically you follow the object movement and add constant translation and some linear movement on top of that (one example - camera is in on a kite tied to the ship, and the rope is progressively loosened).
I think you overestimate the density of stars in the universe. If I remember correctly there are typically a few lightyears between each star (on average).
There would still be a curved orbit around the center of the galaxy. That is a bit like arguing that a mission from Earth to Mars would travel in a straight line because there isn't anything in between them.
How can a ship 100 km in diameter cause any significant dimming of a star, which is 21,980,000 km in diameter? It would have to be pretty close to here and lined up just so perfectly.
Why even assume it's a spaceship and not an asteroid or a rogue planet?
The moon is smaller than the sun, and yet still we have eclipses. It's just a matter of perspective.
The object[s] would have to be lined up. That's why an artificial object intentionally traveling to Earth is in some sense more plausible than an asteroid, which could be headed in any direction.
https://www.reddit.com/r/Astronomy/comments/4waozn/new_paper...
https://www.reddit.com/r/KIC8462852/comments/4w7qfi/ben_mont...
They also contain links to the resulting paper itself