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Show HN: A live map of sunlight on earth (sunlight.live)
74 points by tpaschalis on June 26, 2019 | hide | past | favorite | 52 comments

You'll find this sort of visualization on a lot of ham radio websites, since skywave propagation between two points varies based on the amount of sunlight among other things. For instance, https://www.pskreporter.info/pskmap.html

The Geochron (https://www.geochron.com/about/what-is-it/) is a mechanical map+clock created in 1965 that shows it.

Does more sunlight help or hurt skywave propagation?

It's not quite as simple as that, because there are multiple ionospheric layers with different physical properties that affect RF propagation.

An over-simplified explanation is that the outer layers of the atmosphere persist continuously, and can be used for very long distance communication, but only reflect radio waves at relatively low frequencies (<10MHz). The lower layers that become ionized during the day absorb some of the radio waves, reducing overall efficiency and range, but also allow operation at higher frequencies which would be unusable at night.

And you can get very efficient long-distance propagation along the terminator at dawn and dusk: https://www.qsl.net/w2vtm/grayline.html

"Because the lower-altitude layers (the E-layer in particular) of the ionosphere largely disappear at night, the refractive layer of the ionosphere is much higher above the surface of the Earth at night. This leads to an increase in the "skip" or "hop" distance of the skywave at night."


It's complicated. There are various "layers" of the ionosphere that "bounce back" radio waves in different bands of frequencies depending on the time of day. It's a fun topic to learn about.

This is a really useful visual if one has contacts or meetings in other world cities. The left edge of the light hump is roughly 6am, the center is noon, and the right edge is roughly 6pm. The center of the dark hump is midnight, give or take DST.

Gnome2 had a map like this in its calendar/time drop-down when you add cities to it: https://help.gnome.org/misc/release-notes/2.22/figures/rnuse...

It's one of the main reasons I still use Mate. No other desktop environment keeps it handy like this. I try them for a bit, then always go back to Mate.

It is another cool feature I didn't think about, thanks!

To arrange meetings and sync with remote teams, I'm looking up timetables on a small Go utility.[1]. You can check it in action in the Go Playground [2].

[1] https://github.com/tpaschalis/Golang-practice/blob/master/ti...

[2] https://play.golang.org/p/vYSmZ3oeOLE

Offtopic but MATE is also literally the only Linux desktop that gets multi-head right, especially when it comes to hot-adding and hot-removing displays. All others do weird things to the window layout or crash when you add or remove a monitor while the machine was asleep.

Interesting. Perhaps because it was one of the only ones to stick around long enough to mature, until it was abandoned CADT style.

I always use this tool if I want to check local times: http://www.worldchatclock.com/

Cool, I've used a similar flattened version of this when I had simultaneously global meetings more often. Now my needs are less demanding however.

Interesting that these maps are always binary: light or dark, when the intensity of light varies based on how high the sun is in the sky. Is there a version of this map that takes that into account?

As smackay mentions, there are different 'definitions' of twilight [1], I went with the 'civil' one, which is the most widespread.

The page could be modified to present a gradient, since it only requires calculating the sun's altitude and solar time, which is not that complicated.

[1] https://en.wikipedia.org/wiki/Twilight

Human vision has two logarithmic-response mechanisms in a row: the expanding/contracting iris, and the rods/cones (and many other nerve cells') logarithmic response.

Meaning: you get full visual acuity with just a little light. Further increases often don't even register.

In numbers: typical overcast daylight is around 1,000 lux. Full sunlight is above 100,000 lux.

You would need to have the data of how high the sun is in the sky, plus to be accurate you would need to have cloud data as well.

I'm thinking more of an Irradiance map where the value is the current W/m^2 at a specific location, which would take into account latitude and time of year (to get the angle of the Earth relative to the sun), along with other factors like clouds, altitude.

e.g. https://www.nrel.gov/gis/images/solar/solar_ghi_2018_usa_sca... but on the daily.

As a start, it will be nice to just show the relative intensity of the light ignoring clouds and stuffs ... for example, people should know early morning, mid day and evening from the map which helps which part of the globe is going to get active/inactive

Tangentially related plug for a small site I built to tell you when golden hour is at your location https://whenisgoldenhour.com/ [1]

Would love to figure out how to incorporate a world dot map like this, but showing the two current golden hours (morning and evening) instead.

[1] https://github.com/ksho/whenisgoldenhour.com/

Out of interest - how are you getting location? I didn't get a consent warning for client side geolocation and it seems accurate so it doesn't appear to be IP based (my public IP appears to be a few hundred miles south of my actual location).

I'm using the google geolocation API https://developers.google.com/maps/documentation/geolocation... at https://github.com/ksho/whenisgoldenhour.com/blob/master/pag...

I've gone back and forth on replacing this with a browser-based location request so the user is aware what's going on -- the tradeoff being the friction of clicking the allow button.

Appears to be using google's geocoder [0]

My location resolved a province over, so I suspect it is at least somewhat IP-based (or IP + some other magic)

[0] https://github.com/ksho/whenisgoldenhour.com/blob/3c0d7f0acf...

Looks like it's using Google's geolocation API: https://developers.google.com/maps/documentation/geolocation...

I get 10:26pm until NaN:NaNpm Probably because I am in Northern Norway (Midnight Sun).

Whoa yeah, that bug makes sense. Thanks!

Somewhat related- not quite live, but NASA's DSCOVR is a satellite that is always on the sunlit side of the earth:


Here is another take at the same: http://www.fourmilab.ch/cgi-bin/Earth

I was expecting a map showing the clouds!

I like the one that has the sunlight map plus the live cloud cover feeds - Interestingly enough, this is the site that holds all the linux manpages.


You can actually just link the image to your desktop and depending on settings will auto update throughout the day. Sometimes you need to write a script


Huh, I wanted to draw something exactly like this to put as hero image of my company page, except with ISS orbit instead of the terminator. I really like this "world map out of dots" style.

Thanks! I was inspired by the world map that appears on my android's Clock application, and it was an opportunity to write some structured matplotlib code and learn about new stuff.

You might want to take a look at the Natural Earth [1] datasets and GeoPandas [2], they're great if you're dealing with any kind of geographical data.

[1] https://www.naturalearthdata.com/

[2] http://geopandas.org/

Can't you use a static image on the server and compute the terminator on the client side? That way it would always be up-to-date even without a reload.

This reminded me of a moving city on Mercury called Terminator from Kim Stanley Robinson‘s novel 2312. The city slides along metal tracks propelled by the expansion and contraction of the metal as the terminator of the sunlight shifts. There’s even a sun cult that chases perpetual dawn. It’s a pretty good science novel.

Nice work.

Want another challenge? Try one with the azimuthal equidistant projection. Would be quite interesting to watch the comparison.

In the old days I used use xearth (https://xearth.org/) to set my X background to a view of our planet with the sunlight correctly applied.

There used to be a page that showed the view from a webcam located wherever the sun was currently rising as you viewed the page.

Can't find it any more though - probably been removed.

You can get a live map of where the sun is shining from Google maps. Just switch to satellite view and zoom out until you see the whole earth, then a bit more.

I'd love to use this as a clock pane in my window manager. If you added the local time and removed some of the large text, it would be a great background.

Very nice. It would also be cool to be able to input what datetime you want it to display sunlight for.

Modifying the Python code for this would be trivial. I need to think about how to best serve each 'session' though, or transfer the image generation to the client-side. Nice plan for a weekend!

Poor Antarctica right now.

I don't know off hand what this cliche wave is called(shown in like all SciFi space launch movies) the wider top part of the wave that's the Earth tilted in that direction? eg. northern part is exposed towards the sun more. At this time for me in US.

As cosmic_quanta mentioned it's called the terminator, and it's generally the dividing line between the 'illuminated' and 'unilluminated' part of a celestial body.

You're right, the weird shape is due to the projection of "earth" in the X-Y plane, if you chose a different projection it would appear differently. The calculations make sure that the result is ±1 accurate all year long.

The truth is that even the definition of 'daylight' and 'night-time' is not straightforward. The most common definitions include the Civil, Nautical and Astronomical Twilights [1], depending on the sun's position, so it should actually be a gradient.

[1] https://en.wikipedia.org/wiki/Twilight

thanks for the info, I just see that squiggly line all over that 'sine wave' looking thing on space-related scenes on a big screen.

It is described in the page's About section (https://sunlight.live/about.html). It is called a terminator.

great name haha, I was not aware of this

This would be pretty slick as a new tab chrome extension.

related, and also useful: https://xkcd.com/now/

simple and sweet - quite interesting and useful !

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