Predicted sunset 17:41, observed sunset 17:41

I watched the sun set from my rooftop today and just had to take a picture. The direction is pretty much due south, and the sun is about to set over the mountain called Løvstakken (“the stack of leaves”, so called due to its shape, I guess).

The top picture shows the horizon as seen from my rooftop just before sunset today. The graph is a zoomed view of the computed horizon at suncurves.com.

The clear weather also enabled me to do some on-the-spot verification of the suncurves.com computations. My colleague Paul and I have made a program that computes the apparent horizon from any location worldwide. This horizon is then combined with data for the sun’s path across the sky. The intersections between the two define the times for sunrise and sunset for any day of the year. Our data is obviously a lot more accurate than the standard sunrise/sunset times that you find elsewhere on the web.

But just how accurate are our calculations? Today our program said that the sun would set at 17:41 (see the table in the picture), and that was spot-on for today. We’ve seen that our times are usually with a 5-minute margin of error. When you accumulate that over a full year, which we do to compute what we call a sun index, the results are very very reliable.

If you’d like, you can find your own sunset and sunrise times for places that you care about. The site is free to use as long as you register. Go on, give it a try in our location finder. Or click here to find a list of our demo pages for sites around the world.

And tell your friends about it if you like it – we think a lot of people out there would think that this is cool.

Advertisement

Sun info for house buyers

We believe that prospective house buyers care about the sunniness of the property they’re considering. For instance, they would probably like to know when the latest sunset of the year occurs. And the earliest sunrise?

Sunrise and sunset times can be found on many web sites, but they don’t take shading from nearby hills and mountains into account. And in mountainous regions that matters a lot. So with our background in meteorology, we thought: why don’t we just compute it?

Almost a year later, we’ve now set up a free web site where you can enter any address worldwide, and we’ll compute the actual horizon in a second or two. Here’s what it looks like for the best hotel in the world (according to TripAdvisor):

The picture is taken from the web page that we’ve created specifically for the Grand Hotel Kronenhof in Pontresina, Switzerland, and it shows the 360-degrees horizon as it would look like from the hotel. The path that the sun follows on 21 June 2014 is also shown, along with a table with the key “sun facts” for that day.

You can get a similar page for your own house, cabin, hut, favorite lookout spot or anywhere in the world. Click here to search for it!

You get all the key facts (latest sunrise, average number of sun hours, the number of sun hours that are “lost” due to terrain shading etc.), and we also compute your sun index. This is simply the percentage of sun that you get compared to what you would get if the horizon was completely flat. If the sun index is 50 %, the terrain “steals” half your potential sunlight. We also break down the sun index into monthly values and we compute it separately for the morning and the afternoon.

Here’s what (the top part of) our “location views” look like:

All this for free. We plan to sell PDF modules for agents to use in their brochures, but for personal users, such as house owners or house buyers, our web site is completely free to use. Why, you may ask. It took us a loooong time to compute all this, but for now we just want as many people as possible to know about this. So go ahead and share this on Facebook or Twitter if you like what we’re doing. Thanks!

Sun Maps for Bergen, Norway

We’ve developed a program that computes the horizon at any location worldwide. This enables us to compute the actual sunrise and sunset times for each day of the year. Here’s a map that shows the local time of sunset in Bergen on 21 June, normally one of the longest day of the year:

The sunset times for 21 June in Bergen, Noway

And here’s the number of hours with sunlight on the same day:

The number of sun hours per day in midsummer