Astronomy question re: day/night lengths

[Papageno]

I've always wondered about this, and find no intuitive way of figuring it out: namely, do days get longer or shorter faster near the dates of the solstices or the equinoxes, or do they gain or lose time uniformly from one solstice to the next?

Any astronomy experts want to weigh in?

 

[dzid]

I've always wondered about this, and find no intuitive way of figuring it out: namely, do days get longer or shorter faster near the dates of the solstices or the equinoxes, or do they gain or lose time uniformly from one solstice to the next?

Any astronomy experts want to weigh in?

That's an interesting question. Now you've got me thinking about it. Poking around, I found this:

The rate at which daylight changes daily fluctuates, being most pronounced at certain times and minimal at others. Around the spring and autumn equinoxes, the daily change is fastest, meaning a gain or loss of up to three minutes per day in mid-latitude regions. Conversely, the daily change slows considerably near the summer and winter solstices. During these periods, the sun’s apparent north-south motion is minimal, leading to very slight adjustments in day length, sometimes only a few seconds. This occurs because the sun’s path across the sky changes most rapidly around the equinoxes and least rapidly around the solstices.

 

[Papageno]

That's an interesting question. Now you've got me thinking about it. Poking around, I found this:

Would have never guessed you'd find that on a biology website.

 

[dzid]

Would have never guessed you'd find that on a biology website.

Me neither. I have to admit being lazy, because I got up to ask my dad if he knew. He's the astrophysicist, and I'm most assuredly not. He was already down for the night, and only then did I start searching.

ETA: Asked anyway, and was told the derivatives' peak and valleys of the sinusoidal pattern demultiplexer referred to are where the fastest/slowest rate of gain and loss happens. I think.

 

[demultiplexer]

Day length changes sinusoidally, so the fastest rate of day length gain/loss is exactly equally time distant from both equinoxes. Right now we're gaining day length at less than a minute a day where I live and the peak rate is around 5 minutes per day in March and September

 

[smartalco]

My immediate thoughts on what the answer would be was either of the following two explanations (both really saying the same thing, but one is basic reasoning and the other visual):

First, day length is directly coming from the orbit and rotation of spheres in continuous motion. Any given arbitrary attribute that's derived from that should also be continuous. The rate of day length change going from (for ex) +4 minutes one day to -4 minutes the next day is not a continuous change, so doesn't seem possible.

Second, I have seen and knew that the graph of day lengths over the year is a wave. Random graph stolen from google:

The rate at which the length of the day changes day to day is the derivative of that graph. If the length of the day changed by a static amount every day, then the derivative graph would be a straight and level line, which means that graph would have to have a sawtooth pattern. Since it doesn't, the rate of change is not static. (Side note: the site I grabbed that from also has a graph on the percentage change each day as a proxy for how fast the day feels like it's changing. http://wordpress.mrreid.org/2014/10/19/rate-of-change-of-day-length-with-latitude/ )

 

[Papageno]

In Portland Oregon I'm between the 45th and 46th N parallels, so if it weren't for DST the sky in late June would start getting light in the Northeast around 3:15 AM, so anytime people complain about the twice yearly time change I say fine, make it DST all year: don't stick me with a cacophony of birds squawking outside my open window at 4 AM.

 

[Staubo]

Amatuer Astronomer checking in.

Item #1. You gain/lose daylight the fastest at the equinoxes. It slows to a crawl at each of the solstices, flips, then starts to speed up.
Item #2. The effect is magnified the further you are away from the equator you are. Takes a big swing in conditions to go from 24 hours of darkness to 24 hours of light at the poles.
Item #3. The total 'swing' in daylight experienced is a direct factor on your Latitude. This explains why Arizona can ignore Daylight Savings Time while people in Michigan probably could not live without it.

I give you a tool to explore this more... timeanddate.com in their Sun & Moon astronomical data for a location, provides a wonderful graph showing the changes to sunrise/sunset times over a year. Here is Detroit's. https://www.timeanddate.com/sun/usa/detroit

Note: Because the graph shows Nautical and Astronomical twilight, you can see those bands expand in the summer because of the Northern Hemisphere being pointed at the sun and it taking longer for a location to go completely into shadow.