1030pm, June in Reykjavik |
Woke up really early at my sister-in-law's place. After brushing my teeth and washing my face, it was only 6 am, might as well do some research on daylight in Reykjavik that I promised.
Back to the day we arrived in Reykjavik, we were intrigued still by the daylight hours and found out that there is 24-hour daylight there. Of course, we have to venture out to experience it. Went out after the second seating dinner and walked around the dock area. We got to see the sun still. It was around 1030pm or so. A few minutes later, someone observed that the sun was a little higher, also with photographic evidence. I have to admit that the sun looked a little higher at that later time. That brought on the debate about whether the sun was rising or setting. Traditional wisdom would say that it was setting. Ship brochure said that the sun was going to set around midnight that day in early June. Another question arose in my mind that if the sunset is around midnight and sunrise around 3am, why is there 24-hour sunlight.
You can find anything on the internet nowadays. It took less than an hour.
First of all, the daylight that we see after the official sunset time was the twilight, There are different levels of twilight, the civil twilight when the sun is 0 to 6 degrees below the horizon, the nautical twilight when the sun is 6 to 12 degrees below the horizon and the astronomical twilight when the sun is 12 to 18 degrees below the horizon. Civil twilight is brighter than nautical twilight which is brighter than the astronomical twilight. You can still have daylight when the sun has set (gone below the horizon) because the light from the sun is deflected and scattered by particles in the lower atmosphere and there is different degree of brightness depending how far the sun is below the horizon. In Reykjavik in early June, and even later in June, the sun never goes 6 degrees below the horizon and you can see the civil twilight between the official sunset and the official sunrise.
![]() |
Phases of twilight |
Of course, the principal reason that there are different amount of daylight and darkness is because the tilting of the earth. It takes one year for the earth to go around the sun, tilting the same way. When the earth is tilting towards the sun in the summer, the rotation of the earth for the day will still have one end of the axis always seeing the sun. And Reykjavik is close to the north end of the axis. For lower latitudes, the summer daylight hours are longer. At the same time, the other hemisphere, Australia for example, is tilting away so they are in the winter season with less daylight.
Tried to figure out whether the sun was rising or setting in my head. Could not do it. There is too much geometry to come up with small quantity differences. Internet to the rescue. Found the site www.timeanddate.com which gives the sun and moon location when they are at their zenith (directly overhead). Not too useful for me because I was not there at those locations and I kind of know where to look from Reykjavik but again, hard to figure out the height of the sun from ground. Found another site www.suncalc.org which gives me exactly what I need. Got there by searching 'direction and height of the sun'. It gave me the direction of the sun, for Reykjavik in early June, a little west of north and the height of the sun, 3.3 deg at 1030pm and 2.6 deg at 1040pm. So the sun was setting when we were there! Why did we not see that? My guess is the different scattering of light near the horizon making the sun appeared to be closer to the dark patch underneath but that is not a proof.
![]() |
wk |
![]() |
wk |
![]() |
Jimmy |