Hacker News Reader

Comment by computator | Hacker News Reader

> On June 21 or so every year, Earth’s North Pole reaches its greatest tilt toward the sun. When that happens, the sun’s path across the sky takes it the highest above the horizon all year, making for the longest days of the year and giving the sun maximal time to heat the ground. We associate this time of year with warmth and sunshine.

The duration of daylight can't be the complete explanation for why summers are warmer because otherwise the North Pole and Scandinavia, having super long days, should be hot during summer. He forgot to mention that the angle of the suns rays, depending on where you are, is also a factor for the warmth, right?

Now that I'm thinking about it, which is really the bigger factor in having a warmer climate: your angle to the sun (your latitude) or the duration of the day? (I realize that they are connected, but I'm trying to imagine separating them.)

View on HN

> otherwise the North Pole and Scandinavia, having super long days, should be hot during summer

They are hot during the summer, relative to winter. You’re assuming a particular definition of warmth/heat, but these places do have a summer that is much warmer, the average annual temperature swing of ~25C is similar to many cities in the US and Europe. (Which doesn’t answer your question directly, but does say a little something about the relative importance of angle vs length of daylight.)

*edit, btw check out plots of temperature during the day vs during the year. Angle affects temperature on an hourly basis. [1]

Here’s another article all about sun power vs angle, and mentions atmospheric absorption. Note that while lower surface angles receive less surface energy, it doesn’t change the angle of atmospheric energy absorption, and low angles increase the distance light travels through atmosphere. The atmosphere gets about a third of the sun’s energy absorbed by the earth, the surface gets the other two thirds. [2]

[1] https://weatherspark.com/y/9847/Average-Weather-in-Kansas-Ci...

[2] https://en.wikipedia.org/wiki/Solar_irradiance

> which is really the bigger factor in having a warmer climate: your angle to the sun (your latitude) or the duration of the day?

This graph from wikipedia might be a good start. It is showing the trajectory of the sun on different days of the year at 56 degrees north latitude (e.g. Edinburgh, Scotland).

https://commons.wikimedia.org/wiki/File:Solar_declination.sv...

The horizontal axis is the azimuth of the sun, but it works as time as well. So that tells you the duration of the day.

The vertical axis is the elevation angle of the sun. To turn this into a solar power factor, you would actually have to take the sine of the angle. But I don't think that would change the overall shape of the graph much.

So you can think of the area under the curve as an approximate measure of energy delivered by the sun.

In the summer you have both effects - you have more direct sunlight (more vertical angle/less atmosphere attenuation) as well as the longer days. The higher apex of the sun in summer is a sign of the former as well as the latter.

You are correct. Insolation:

https://www.sciencedirect.com/topics/earth-and-planetary-sci...

I read somewhere that the hottest mix of the two is around 30 degrees.

> around 30 degrees

The Horse latitudes. [0]

Having spent a significant amount of time ~at this latitude, I'm inclined to believe it.

[0]: https://en.wikipedia.org/wiki/Horse_latitudes

Reply on news.ycombinator.com