A new paper on prior observations of KIC 8462852 deepen the mystery surrounding this star. Also known as “Tabby’s Star”, this F3-type star is brighter, hotter, and more massive than our sun. The mystery lay in the sudden dips of luminosity seen by the Kepler Space Observatory. Kepler’s mission is to detect earthlike planets transiting distant stars.
Speculation about this object captures our imagination, with Jason Wright suggesting it could be evidence of an alien megastructure in his paper The Ĝ Search for Extraterrestrial Civilizations with Large Energy Supplies , while others claim it’s just comets.  The basis for arguing this is artificial stems from the lack of flux when it dims. If the cause was natural, like a cloud of cometary dust, the dimming should be gradual rather than abrupt.
Recent attempts to detect the extraterrestrial intelligences behind this anomaly have fallen flat. No radio signals were detected by the Allen Telescope Array between the 15th and 30th of October 2015.  Between the 29th of October and the 28th of November, weather permitting, the Boquete Optical SETI Observatory joined the fun. But astronomers didn’t detect any periodic optical signals one could ascribe to alien communications.  Barely two months of observations of an anomaly possibly a thousand years old is merely a drop in the bucket. Yet the absence of evidence from this dataset only emboldens those pushing their comet agenda. Which reminds me of a soundbite from Jill Tarter’s 2009 TED Talk on the search for extraterrestrial intelligences:
All of the concerted SETI efforts, over the last 40-some years, are equivalent to scooping a single glass of water from the oceans. And no one would decide that the ocean was without fish on the basis of one glass of water. 
While SETI may only have forty years of observations, traditional astronomers are sitting atop a mountain of photographic evidence collected since the 19th century. Tabetha Boyajian, author of the original paper KIC 8462852 – Where’s the flux?, knew this and took advantage of the archives at the Digital Access to a Sky Century @ Harvard (DASCH) for past data on KIC 8462852. DASCH is a treasure trove of digitized astronomical photographic plates from previous sky surveys from the late 19th century to the present. Upon review, her conclusion was summed up as “the star did not do anything spectacular over the past 100 years” 
Bradley Schaefer disagrees with her conclusion, having pored over the plates himself. His findings are outlined in his new paper at arXiv.
The KIC8462852 light curve from 1890 to 1989 shows a highly signifcant secular trend in fading over 100 years, with this being completely unprecedented for any F-type main sequence star. Such stars should be very stable in brightness, with evolution making for changes only on time scales of many millions of years. So the Harvard data alone prove that KIC8462852 has unique and large-amplitude photometric variations. 
Dumbing it down a bit more, the anomaly’s been gradually dimming the star over the past 125 years. For the extraterrestrial faithful, it supports the hypothesis of little green men engaged in one of the universe’s largest public works projects this side of the Death Star. Just as Jason Wright, et al., riffed on Boyajian’s discovery, Chris Lintott and Brooke Simmons let their imagination run wild with Schaefer’s evidence at the Journal of Brief Ideas.
We assume our observations cover a typical period in a constant construction rate. Given the current B magnitude of 12.262 and a decrease in flux of 0.165 mag (or 14.099% of total observed flux) per century, an alien civilisation requires at least 7.09 centuries to occlude 100% of the observable surface of its star. Thus, if this time is typical, an alien civilisation capable of constructing such a structure requires a minimum of 1400 Earth years to do so. 
Regardless of what’s behind this, whether aliens, comets or something completely different, the mystery behind KIC 8462852 isn’t going away anytime soon.