@astrosnapper's answer to the question Could stellar occultations be used to survey Kuiper belt objects? mentions the TAOS-II project and asteroid occultation measurements (which occur on the timescale of seconds) and that got me thinking about the term Time Domain Astronomy.

A quick search led me to an Astrobites post with a catchy title A Big Step Backward for Time Domain Astronomy that (among other things) describes the DASCH project (Digital Access to a Sky Century @ Harvard).

The post is dated 2012 and says:

The project is working to (1) digitally scan all of the plates, (2) detect sources on the plates, (3) assign physical coordinates to the plates, and (4) measure/calibrate the magnitudes of all sources. The end product will be a publicly available database which can be queried to produce the 100 year light curve for individual objects. As a part of the project the team had to develop a specialized scanner, as commercially available units would have been too slow to finish the project in anything resembling a reasonable amount of time. As it is, when operating at full efficiency, the project can now scan and analyze 400 plates a day. As of the writing of this article, 38,346 plates have been scanned (~8% completion; see Figure 2 for a map of their current coverage) and over 2.7 billion magnitudes have already been measured.

The article ends with:

...Given that we’re only 8% of the way through analyzing the plates, we can look forward to further interesting discoveries from this survey in the next few years.

It is now six years later. Presumably the scan rate has accelerated a bit and a much larger fraction of the plates have been scanned, and techniques for reducing and analyzing the huge amounts of data have improved as well.

Since 2012, what new discoveries have been made from this effort? There may be too many to list, so a few highlights and a link to a summary might be the best way to answer.


The most notable one I'm aware of is the detection of the secular dimming of Boyajian's Star (KIC 8462852), as described in Schaefer (2016). Follow-up by Schaefer et al. (2018) suggest that the ratios of the dimming across the BVRI bands are consistent with dust, though the reason for the lack of detectable infrared excess remains unknown.

DASCH data has also been used to constrain the orbital period of the ringed object transiting J1407, see Mentel et al. (2018). The DASCH plates did not show any previous transit in the data, ruling out a large fraction of orbital periods and opening the possibility that the ringed object J1407b may not be gravitationally bound to J1407.

  • $\begingroup$ Thank you for your quick reply! Can you add some of the information in your links back into your answer? Right now this is almost a link-only answer. If and when the links rot and break the value of a link-only answer disappears. Both of those are available in ArXiv (1, 2) so it shouldn't take long. $\endgroup$
    – uhoh
    Jan 5 '19 at 12:13
  • $\begingroup$ @uhoh - if ADS breaks their links or goes offline there will be substantial problems anyway... so far they've been running since 1992 so hopefully they will remain stable for a fairly long time to come. Nevertheless I've added a bit of detail, hope that helps! $\endgroup$
    – user24157
    Jan 5 '19 at 12:28
  • $\begingroup$ I'm just explaining best practice for writing a Stack Exchange answer. Thanks for the edits! $\endgroup$
    – uhoh
    Jan 5 '19 at 12:32

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