Wednesday, March 28, 2012

13 h

Length of day is now 13 hours, which is rather nice: sunlight in the morning and quite long daylight time during the evening.

Today I forgot to take a spare battery for the camera, and I couldn't take many photographs while commuting. Typically the battery lasts for about 1200 photographs, but I usually remember to check the charge each day.

Anyway, after work I went for a 1 1/2 hour walk with the daughters, and took some photographs. We have had it warm, and snow is now disappearing fast. The official depth of snow figure at the Vantaa airport is 28 cm, but in many places there is almost no snow on the ground left.

PS. By the way, one of the Finnish weather forecast sites says that the length of day is 13 h, and the other 12 h 59 min. I always wondered why it is the weather forecast sites which show this info, and why there are differences.

But then I read that in fact the length of day is also forecast, namely it depends on how the light bends in the atmosphere, and the air pressure plays a factor there. The daylight time is the time between the moment when the upper edge of the sun crosses the horizon to the moment the upper edge disappears below.


Christophe said...

Well, if you want another value, you can look at the sun calculator at
It is so much accurate that the length of the day is 12:58:30 in Helsinki, 12:58:35 in Espoo and you lucky guy so much more north of us got 12:58:47 today in Vantaa!

Juha Haataja said...

@Christophe: The precision of seconds is a bit overkill, as the weather conditions affect the sunset and sunrise times by quite a lot, so a precision of more than a minute is meaningless. But still it is nice to not that the day is longer here in Vantaa.

FMI is making predictions each day, and that is why their estimate for the length of day differs from the "standard" calculations, sometimes it is less and sometimes more.

Today Foreca gives 13 h and 5 min and FMI 13 h and 4 min as the length, yesterday Foreca gave 12 h 59 min and FMI 13 h 0 min.

The biggest factor is the water vapor content in the atmosphere, not air pressure as I originally wrote.