Scandinavium #1: Sunlight, moonlight, and starlight
{800 words, 4 figures, 5 minutes}
"Scandinavium" is a regular column where I write about the elements of daily life in Norway and broader Scandinavia.
The sky at 8:41 PM on August 5th, 7 minutes after sunset.
Of course, the first thing you notice when you spend a night in Norway during the summer is the light. The daylight is so long that it's 9 or 10 PM and you can still see things very well outside. It's not until 11 PM that you get a familiar darkness but it's short-lived. If you're (un)lucky enough to be up at 4 AM or so, you'll notice it starting to get light outside again and by 5 AM, you'd be able to walk and drive without lights on.
To better illustrate the extremeness of this phenomenon, let's look at some technical data. Here's the astronomical data for August 13th in Kjeller, Norway (CEST stands for Central European Summer Time).
First, a few definitions.
- Actual time means sunrise and sunset.
- Civil twilight is when the sun is between the horizon and 6 degrees below the horizon. In your daily life, this is dusk (and a beautiful time for photography). It means that between these times, you can be outside, do normal things, and see without difficulty even though the sun has technically already set. For astronomical purposes, it means that only the brightest stars can be seen, excluding other factors like moonlight and light pollution.
- Nautical twilight is when the sun is between 6 and 12 degrees below the horizon. In your daily life, this is time to go inside (or when early birds start to go to work). You can still see the horizon and you can sort of make out the outline of things in the dark, but if someone throws a frisbee at you, you're likely to have a hard time seeing it and catching it.
- Astronomical twilight is when the sun is between 12 and 18 degrees below the horizon. In your daily life, this is the dark, sacred night that we like to sleep in. For astronomical purposes, this is prime time for seeing stars since the Sun will no longer have any effect. A telescope has the best chance of seeing the faintest stars during this time.
Not sure how big a degree is in the sky? Stick your arm straight out at the horizon and make a fist like you're holding a ski pole. The amount of sky that your fist covers is about 10 degrees. The horizon is zero degrees and straight above your head is 90 degrees. Since your fist is about 10 degrees, sticking two fingers out marks 5 degrees.
The "Rise" and "Set" times might seem odd because they take the perspective of "twilight" for astronomy, meaning you can't see the faintest stars starting at 1:53 AM until 12:48 AM the next day. In case "Rise" and "Set" times are confusing you as they do sometimes me, just switch them around. Astronomical twilight (the dark of night) starts at 12:48 AM and ends at 1:53 AM. Not very long in Kjeller, Norway!
There are two more things to notice in that figure. The obvious one is that the length of visible light is incredibly long: 17 hours and 31 minutes. Secondly, the length of day will be 5 minutes and 11 seconds shorter. Why? This is because we've passed the summer solstice in June and are headed toward the winter solstice in December. Each day gets slightly shorter but we generally don't notice it until we get jolted by the end of Daylight Saving Time in November. Once we hit the winter solstice, this statistic will change and each day with get a few minutes longer.
Actually, we only recently got astronomical twilight here. A few days ago when I checked the astronomical data, Kjeller looked something like Tromsø, a large city in northern Norway, above the Arctic Circle (albeit we still had nautical twilight):
Courtesy of www.wunderground.com. If you're an astronomy nut like me, seeing the words "Sun does not set" is kind of spooky when you're used to seeing a time there.
Also note that Tromsø's length of day is a whopping 10 minutes and 26 seconds shorter. This was later a "duh" moment for me. If the polar ends of the Earth are known for extreme lengths of day and night, but have the same number of days in between solstices as everyone else, each day has to change a lot more. For comparison, look at Atlanta, GA:
After years of checking the weather and astronomy data in Atlanta, I was very used to seeing 1 or 2 minutes of change in length of day. Five minutes is a shock to me and I can't imagine what 10 minutes would be like in Tromsø. In one week, the length of day would change an entire hour! But if the sun shines all day, perhaps it is also hard to tell until one is jolted by Daylight Saving Time.
Well, that's all for now. I hope you learned something interesting. I didn't get to talk about the Moon much so maybe I'll save that for another time. Thanks for reading and see you next time.
