Hengefinder: Finding when the sun aligns with your street | Hacker News Reader

Hengefinder: Finding when the sun aligns with your street

victoriaritvo.com

201 pointsevakhoury45 comments

It would be nice to be able to access the website on a smartphone (even if the experience is suboptimal), instead of denying access.

Thanks! This is updated now, and you should be able to access the website https://hengefinder.rcdis.co/ on mobile. You can also download the app with more features at https://hengefinder.com/

Smartphones have the huge advantage of direction sensors (3D magnetometer and gyro). I remember using apps like Google sky map (or something like that) way back in 2011 to look at satellites and planets.

Not sure if this is the app you were referring to, But Stellarium does exactly what you're describing.

There's a mobile app that supposedly works worldwide (but isn't available in my country).

Really wish mobile browsers were better liars when it comes to "desktop mode"

Seriously. Plus, what is the problem that some websites are 'fixing' by denying me a choice in how the website loads?

That they’ve chosen gaps between components that are larger than your device screen,

and they either functionally can’t,

or simply don’t want to,

adapt their poorly-designed webapp frontend to.

I need the inverse of that - an app that predicts how badly a given street will be baked by the sun at current or near-future time, will there be any shadow zone from the buildings, how far will the usable extent of it reach (e.g. not much use of shadow if my head or body stick up beyond the shaded volume). Ideally available on a smartphone. Bonus points for being able to route navigation paths to minimize direct sun exposure.

Motivation: I hate it when it's hot, but my kid has actual issues with heat/sun exposure, and e.g. I had to navigate our way around the city through shaded zones today, just so she doesn't get exhausted in under 30 minutes.

Plenty similar apps are made to sell people photovoltaics, but I'd love to see something to help humans avoid sun.

There’s a few sites that do what I think you’re asking for, not navigation though. This is one I’ve used recently: https://shademap.app/

This is exactly what I am working on for my city (Berlin). Right now it gives you sun/shade times for outside areas of cafes and restaurants as well as heatmaps for public parks and playgrounds.

The idea is to eventually offer a sun or shadow mode and the app will then surface areas, squares, and streets with more sun or shade and eventually offer walking and biking routes with more or less sun.

This could also be a legitimate lifesaver in places like India where extreme heat is common but delivery and gig workers have to travel outdoors.

Update: I just vibe coded myself one, gave me an excuse to play with Antigravity (and then cleaned up/improved with Claude Code). Not posting a link yet because it serves 12MB worth of geo JSON up to the client on first page load, and I'm not eager to wake up tomorrow with a bill for upload traffic spike. But it pretty much does its job as well as it could given quality of available data (OSM), so now I'm looking at improving the data itself.

It currently runs A* for routing between two points on map (no address lookups yet), using either local A* or an OSMR endpoint for base path, and then A* for shadow-aware routing, and shows both, + stats (total time exposed, how much it saves in sunlight exposure and loses in time relative to base), plus has a bunch of debugging overlays so I can validate and diagnose pathfinding and data quality. But I tested it live today, and it mostly checks out with reality (big gap: no data on trees).

If you hadn't already, I would have suggested vibe coding this.

I've done a different thing also with OSM data (isochrone rather than point-to-point routing) and put it on github to avoid needing to care about bandwidth on my domain, because also around ten megabytes for Berlin's data, despite having a step to convert JSON to a much more compact form with only the data I needed:

https://github.com/BenWheatley/Isochrone

https://benwheatley.github.io/Isochrone/web/?region=berlin&n...

It uses the Python lib Astral, which uses "equations from Astronomical Algorithms, by Jean Meeus", to find location of the Sun in the sky. That method assuming earth motion without gravitational pull from other planets or the Moon, and has accuracy of 0.01 arc degree. Meeus is a rock star in these kinds of calculations. He also gave a truncted version of VSOP87 that has error less than 1 arc second in finding Sun's location.

The method Astral uses for calculate Moon's location has precision of 1 arc minute. For higher precision, LEA-406 [1] can be used.

[1] https://www.aanda.org/articles/aa/full/2007/33/aa7568-07/aa7...

Interesting, I've planned similar shots before and used different tools that serve a similar purpose. The Photographer’s Ephemeris has nice visualizations: https://photoephemeris.com/

NASA's Horizons ephemeris is also pretty good at preparing data for this. I've used it with a little script to check when the sun/moon will be in a given box. This hengefinder looks neat and really streamlined for its purpose though.

I lived a long time in a city near the equator with a prominent east-west street. Commuting west to east in the morning and east to west in the evening meant frequent hengings. The roads don't feel particularly safe when you can't see anything. The town planners might have considered this.

Any angle within 23º of east-west will have henging at some time of year. You'd have to have the entire street grid be aligned diagonal rather than cardinal.

Living in the US Midwest, there are lots of towns that are laid out on north-south grids, including portions of mine. As a cyclist, I take note of the days when the sun is coming up over east-west streets, because the car drivers can barely see where they're going. I once saw a multi-car crash on my own street (fortunately at very low speed) that I attributed to this effect.

Additionally I have visited Stonehenge and it's sterilised and disappointing being unable to walk amongst the stones. Thank you for your attention to this matter.

It would be good to also have the option for alignment with sunrises in addition to sunsets.

For instance in Houston the sunrise aligns with Texas Avenue around the June solstice.

Consequently, there are no sunset alignments for the downtown skyscrapers.

Hello, thank you! That option already exists: On the website version, it's available in the "Henge Near Me" tab. You can toggle between Sunrise and Sunset.

There are more features on the mobile version, and it also includes Sunrise and Sunset. Just hit the gear icon on the top right, and toggle between Sunrise and Sunset. Hope that helps!

This looks good and now I think my memory was about 180 degrees off, in Houston it must have been the winter solstice when I saw this one morning.

Your app gets very close but not quite there on the 22 DEC inflection point, I would think the date is correct but the angle is a couple degrees short when the limit is approached. At this latitude it looks like the effect is visible for a day or two before & after the closest alignment.

I'll be checking when the time comes but I was hoping it was only going to be a month from now :\

Various apps for (primarily) photographers offer views of the sun's (and moon's) path, even with live view through the camera.

For example https://www.sunsurveyor.com/ or https://www.photopills.com/ best among others

Very interesting, but sounds like an extra complication to use binary search on time to find the right position of the sun, when you can just directly calculate this, eg. using the formulas in here: https://gml.noaa.gov/grad/solcalc/solareqns.PDF

On a similar note, for this August's total solar eclipse (in Europe), I 3D modelled the sun's position in the sky from the viewpoint that I am planning to go to. The eclipse will happen late in the day when the sun will be low, so I wanted to make sure that nothing will obstruct my view!

I've been meaning to post about it.

Stonehenge of course, famously not a henge.

Apparently the word "henge" comes from the name Stonehenge but Stonehenge has the ditch on the wrong side of the bank to technically be a henge.

For any other curious people: https://www.english-heritage.org.uk/visit/inspire-me/what-is...

Ye - also the henge is the circular ditch, not the stone circle or whatever in the centre

Mobile app not available in your country. :(

then use a stick™

hint, watch the sticks shadow

other hint, can use almost anything that casts a shadow, as a stick substitute.

* even more hints availible with stick™ pro

I’d like to subscribe to stick™ pro! I tried a piece of string and it waved around in the wind and didn’t work, so I think I may need a paid service for this.

your in luck due to a need to redirect our efforts we are opensourcing, stick™ and stick pro, under the historic source code "anelemma" which is stick™ plus rocks™

instruction manual:place stick verticaly on planet. observe shadow™ and place rock™ at point of of maximum shadow length, each day continue untill the pattern starts to repeat. reverse engineer orbital dynamics and gravitational atraction from resulting pattern. scratch head. build civilisation.

Thanks for flagging! This should be fixed now.

It doesn't work with curved streets.

Any sufficiently small section of the street is indistinguishable from a straight street.

Tell that to all the buildings blocking the light

Yep, if I use street name it attaches to wrong part of the street, if I use a place next to the street it attaches to the place, not the street. Couldn't figure out how to drag the origin point of the arrow

The sun?

Nice, and awesome that it works internationally. One little feature request: provide an .ics download, so that I can add a calendar event, add a link to the original calculation to the the calendar entry.

Hi, thank you! The feature to add to your calendar exists!

In the mobile app: long tap on map to drop the pin + alignment arrow. Move the arrow to the line of the road. The "Henge Information" panel slides up from the bottom and has an option to export the henge date to the calendar.

If you're using the website version: it's in the "find a henge" tab. Once the henge is found, you hit "Add to Calendar"

Manhattanhenge is cool but people standing in the middle of street for it is pretty nuts.

it’s nuts that more streets in manhattan aren’t pedestrianized

this is true

older, better alternative: https://suncalc.net/

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