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Couldn't it be just a relatively large object, anywhere in the interstellar space between the star and Earth? I mean, look out the window at a far away car or a tree, then stretch out your hand and you can block it entirely with your thumb. What if the thumb is that object (a planet, a star, a comet, some space debris, etc.) that's between Earth and the star, and it's just the right size to only block that star, and no other stars. Why has this very simple explanation been ruled out (if it has been)?

I know that the debris next to the star explanation has been ruled out because of the lack of IR that would come from that debris being heated up if it was close to the star. But this is not a problem here, if the blocking object is far away from the star.

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  • $\begingroup$ The problem is that the dimming is repeated. It would require a swarm of objects in our Oort cloud passing by this star, but no object passing by any of the other 150,000+ stars which Kepler has observed for years. And I hope someone will explain what effect such a passage would have. Maybe brightening due to gravitational microlensing instead of dimming? I know that they try to find Oort cloud objects with microlensing in Gaia data. $\endgroup$
    – LocalFluff
    Oct 21, 2015 at 7:13
  • $\begingroup$ Why only by the Oort cloud... why not anywhere at all between Earth and KIC 8462852? $\endgroup$
    – sfdglksdfg
    Oct 21, 2015 at 7:17
  • $\begingroup$ Why repeatedly over years and why only this star? (I think it is something wrong in the electronics, a bad pixel on the CCD.) $\endgroup$
    – LocalFluff
    Oct 21, 2015 at 7:38
  • $\begingroup$ The Wikipedia site on the star gives some explanation en.wikipedia.org/wiki/KIC_8462852 but I think it's safe to say there's still a good deal that's not known. I think, objects close to the star, perhaps falling into the star are more likely than more distant objects blocking the star. I think the "intelligent life" argument is pretty weak, personally, but it's worth taking a closer look. Small stars in general are much more variable than large ones. $\endgroup$
    – userLTK
    Oct 21, 2015 at 9:58
  • $\begingroup$ LocalFluff -- I think the authors looked pretty carefully into the question of instrumental effects (Section 4.1 of their paper summarizes this). $\endgroup$
    – Peter Erwin
    Oct 28, 2015 at 17:27

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The simplest reason why your proposed explanation is not really that obvious, and thus was not considered is that the dimming of KIC 8462852 was not an isolated event. The dimming is a pattern that has been observed over years. There is no known phenomenon in interstellar space that would cause a repeated obstruction of that star, so it doesn't make any sense to consider that possibility when there are other phenomena (such as those captured in Boyajian's paper) that are more likely to be the source of the dimming.

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As others have said, there is repeated dimming of the star, that suggests something in orbit around the star. But in addition to that, you are having the perfectly reasonable and common failure to comprehend the vastness and emptiness of space.

Now, comets, planets and the like are quite common going around stars, but in interstellar space they are very rare and to line up exactly with a distant star is incredibly unlikely. To get an idea of the scale, think of the shadow cast by a flea in London, from a light bulb in Beijing, being seen in New York. It just doesn't happen. Because the distances are too vast (even this example is wrong, by a factor of about 1000). Space is just too big and too empty for random debris to exactly line up with a star.

Now if the debris is near the Sun, as is passes in front of a star, the light from that star is abruptly cut out. This is called an occulation, and they happen very often. The conclusion is that whatever is causing the dimming of this star must be close to it. Probably a cloud of dust in orbit around the star, but this doesn't explain how that dust got there, and why it doesn't appear in the infrared.

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    $\begingroup$ I can see where you are going with this view, but does the "to line up exactly with a distant star is incredibly unlikely" argument not work both ways in the sense that whatever the explanation it has not been seen before (unless its the multi-star system idea such as KIC 4110611), so all candidate explanations must be for some phenomenon that would be rare to observe. $\endgroup$
    – Puffin
    Feb 4, 2016 at 17:28
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The OP's "simple (and obvious) explanation for the dimming of KIC 8462852?" is unlikely to work as there very likely is no single simple explanation.

The May 2017 Scientific American (pp. 30-35) has an article on KIC 8462852 (also known as Boyajian's Star or Tabby's Star). which reviews recent thinking on a variety of explanations.

While the article concludes that more information is required, I wonder why we should expect a complex phenomenon to have one explanation.

In my view: the simplest, and to me most obvious explanation, is that it's a combination of a number of mechanisms, some, like the stars dimming, may be intrinsic, others may rely on some inhomogeneous materials (at possibly more than one intervening distance) to be irregularly occluding light from the star.

UPDATE: Looking at the other entry in StackExchange on this topic post 19136 it appears that there's an arXiv post from 2016, not referenced in the Scientific American article, by Jason T. Wright, Steinn Sigurdsson "Families of Plausible Solutions to the Puzzle of Boyajian's Star", which appears to have anticipated the (admittedly obvious but perhaps understated) idea of multiple solutions.

Another useful summary is Wikipedia

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