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Comment by pphysch | Hacker News Reader

Article says the image is from a 503 day exposure--it doesn't say how, if at all, the nighttime data is decoupled from the daytime data. Perhaps it is something like "technically 0.0001% of this image might be from nighttime readings".

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This article is quite old but a more recent measurement from the same experiment (Super-K) used a 1600 day dataset. Of that 1600 days of exposure 860 "days" were nights. So it's pretty close to half and half. (Cite: Section V-B, bottom left of page 22, of https://arxiv.org/pdf/1606.07538.pdf )

The daytime data and night time data are decoupled quite easily. Whenever an event is recorded by the detector you just make sure a timestamp is associated with the event. Then you use that timestamp to determine the location of the sun at the time of the event. If the sun is below the horizon it's "night" and if it's above the horizon it's day.

Looks like Figure 17 is the updated analog of the original HN article-figure.

The detector is deep underground (1000m) so it always goes through a bit of the earth. But they can easily select only the parts of the raw data which correspond to neutrinos going through the whole earth by only using detections which happened at night, local time. I guess they didn't mention this because it's obvious?

For neutrinos there is no nighttime. The neutrinos are captured when they need to travel the maximum distance through the earth. That way, there are fewer other particles that need to be distinguished from neutrinos.

There is no nighttime, nutrinos go straight through stars and planets.

There is in principle a day-night effect which may be measured. The electron flavor component of the neutrino can be enhanced or diminished by the presence of matter.

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