What causes the cyclical nature of the hashrate?

[soy]

There's a periodicity to the hashrate (https://blockchain.info/charts/hash-rate?timespan=30days&showDataPoints=false&daysAverageString=1&show_header=true&scale=0&address=).  I wonder what causes it.  The tides and moon?  Or has higher math found periods of greater block discovery that effectively have those in the know shutting down and restarting their miners to better profit?  The experimental method could prove it true or not if one had the math to calculate the points of inflection then just piggyback on their effect to the hashrate.  Two equal clusters of miners, half on the upper half of the cycle and half on the lower would show if one or the other turned more profit. If so I doubt they'd tell us.

[philipma1957]

There's a periodicity to the hashrate (https://blockchain.info/charts/hash-rate?timespan=30days&showDataPoints=false&daysAverageString=1&show_header=true&scale=0&address=).  I wonder what causes it.  The tides and moon?  Or has higher math found periods of greater block discovery that effectively have those in the know shutting down and restarting their miners to better profit?  The experimental method could prove it true or not if one had the math to calculate the points of inflection then just piggyback on their effect to the hashrate.  Two equal clusters of miners, half on the upper half of the cycle and half on the lower would show if one or the other turned more profit. If so I doubt they'd tell us.

I tell you what  I have avalon6's  and when I reboot they have a very big spike on the onset. Say 14th vs 8th it actually lasts for a minute or two.

  It does show up at the pool I mine at.

Soooo  I do 1 reboot a day sometimes 2.

[soy]

I see.  Thanks.  A large farm may do something similar is a guess.  I myself have an S3 that has a falling hashrate that settles out at 398 GH/s.  I had written a short script, mostly copied from another user who posted his some years ago, to have it reboot at a hashrate of my choosing but eventually thought it a bother and stopped it running on crontab.  A 6TH spike.  That's something.

[xhomerx10]

It's simply variability.  Hash rate is estimated based on the number of blocks found in a given time period.