Diet Darkness

[Mark Wagner]

I was just checking this.  Tonight astronomical twilight begins at 22:00 and ends at 22:52(!!!!).

Darkness will have reduced to 4 hours 34 minus.  Where I am.  Further you go north, the less you get.

Ironically this tends to be most reliable weather for astronomy, now.

Who thought this up?  What a counterintuitive hobby!

[Francesco Meschia]

Astro twilight ends when the Sun id 18 degrees below the horizon, right? That’s more like 22:30 for the Bay Area.

A related cool observation: last Friday I was at LSA, and sunset calculated for that location was 20:21. On the same evening in Mountain View it was 20:30. 9 minutes of difference. 4.8 of those can be attributed to the difference in longitude between the two locations, but the rest is due to the shape of the terminator at the two different latitudes.

I wonder how flat-earthers explain that.

Francesco

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[John Pierce]

On Tue, Jun 16, 2026 at 12:48 PM Mark Wagner <itsmar...@gmail.com> wrote:

I was just checking this.  Tonight astronomical twilight begins at 22:00 and ends at 22:52(!!!!).

Darkness will have reduced to 4 hours 34 minus.  Where I am.  Further you go north, the less you get.

Here in Santa Cruz, at 37N, 122W, I show sunset as 8:29pm, astro dusk at 10:22pm, and astro dawn at 3:55am tomorrow, by my calculations that's 5.5 hours of dark 

[Mark Wagner]

I'm using the astro phone app Daff Moon - I assume its using my location Los Gatos.

For June 16 (with my phone's location) it shows Astro Twilight begin 22:00.  Dark (night) 22:52.  That's 1 hour 8 minutes dark by midnight.  Change to June 17.  Astronomical twilight 03:26. That's 3 hours 26 minutes dark from midnight.  That's how I came up with 4 hours 34 minutes.  I'm not counting from the beginning of evening astro twilight to end of morning morning astro twilight.

Unless the app is wrong, somehow.

Point is still, crazy short.  But best conditions.

And we repeat the crazy every year.

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Mark

[Francesco Meschia]

I think the app may be wrong. If you use your favorite planetarium app, what’s the elevation of the Sun at 22:52?

Sent from my iPhone

On Jun 16, 2026, at 13:16, Mark Wagner <itsmar...@gmail.com> wrote:



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[John Pierce]

On Tue, Jun 16, 2026 at 1:16 PM Mark Wagner <itsmar...@gmail.com> wrote:

I'm using the astro phone app Daff Moon - I assume its using my location Los Gatos.

For June 16 (with my phone's location) it shows Astro Twilight begin 22:00.  Dark (night) 22:52.  That's 1 hour 8 minutes dark by midnight.  Change to June 17.  Astronomical twilight 03:26. That's 3 hours 26 minutes dark from midnight.  That's how I came up with 4 hours 34 minutes.  I'm not counting from the beginning of evening astro twilight to end of morning morning astro twilight.

at 10:52pm tonight, the sun is 21.5 degrees below the horizon here in Santa Cruz.  At 10:22pm, its 18 degrees below the horizon.    I thought Astronomical Dush is -18 degrees. (and astronomical twilight is -12 to -18)

[Mark]

Ah, I see the app is set for 41'14"N.  Thanks guys.

[Peter Natscher]

This whole thing about observing during the longer-day summer months is a circadian rhythm issue with me at 76.  During June and July, most of the astronomy window extends after midnight.  This is getting more and more difficult for me to feel comfortable with in staying up that long at night after a full day, rather exausting doing multiple night's at a star party. Not natural or healthy.

[Mark]

It's one of the primary reasons I stopped doing multi day events Peter.  And the partying to compound things.  I finally realized fun was no fun.  Two nights seems right, now.  I know some folks are looking at ten nights.  Recovery from that might take a few weeks!

[Peter Natscher]

You're right, two days back-to-back is my max for observing. Two days at Calstar is enjoyable.  Would two nights at GSSP work for me?  The driving distance to shortened observing time ratio doesn't work with this. It's a lot of driving from Monterey but I like road trips and I get to see people I haven't seen since my last GSSP in 1019. It all depends on the weather. Temperature forecasts into the 90's and I'm not going. 25 years of Monterey living has made me more adverse to hot weather.

[Alex]

I think that is commonly known as "jet lag"? I believe the inner rhythm just needs a gentle kick after the prolonged "travel" in a different circadian phase to get back on track. I'm simply taking a good walk then a good nap in the middle of the day at GSSP (eyeshades, earplugs,...; and surely unless you are jogging every day already!). The brain is actually quite easy to fool around with that problem because it does not actually have a sense of Time. :) Surely, I can't vouch for a 76 years old brain, I recall people might have severe insomnia by then getting in the way of this method? I'm 57 and still sleeping like a baby any time of the day/night if tired.

[Mark Wagner]

On 6/16/2026 14:22, Alex wrote:

I think that is commonly known as "jet lag"?

I don't think its jet-lag.  I've had that.  This phenomenon is quite normally associated with aging.  My sleep over the years has changed from solid 8 hour to 6 and now often under 5.  I wonder if it is headed to Insomnia Plague, and worry about the potential for amnesia.

Anyway, the inability to sleep would seem a benefit to amateur astronomers.  Other than fatigue.

[Peter Natscher]

Sleeping at home in routine bedding/environment and sleeping in a 90-degree+ field at 4,000 ft. elevation inside a hot tent or vehicle is not the same. More physical adjustment is needed.

[Peter Natscher]

Dehydration is a primary concern regarding how you physically feel in a star party environment. It causes a lot of symptoms.

[Jay Freeman]

Changing the subject briefly: The thing to do with flat-earthers is to dial up a webcam view of (e.g.) Sydney Harbor Bridge ...

-- Jay Reynolds Freeman
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[Akarsh Simha]

Yep, I ain’t gonna meet Kingsley criterion after 4 clear nights!

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