Very good made! I recently started astrophotography, it is a lot of fun. Just learning all those different stars and galaxies, it's incomprehensible how big is the space. Nice thing it's really doable to appreciate it live from your backyard. A lot of technical things are still desirable, a big opportunity for innovative ideas.
An often used algorithm for the calculation of the apparent sun position (given a date and latitude/longitude of the observer) is SPA of Reda et al. [1].
If you're interested, I wrote an Android app (Sun Locator [2]) that implemented this algorithm.
It's like I just read an epic story, still under impression ...
Quote: One day we’ll colonize other planets, those planets will have different suns, orbits, and rotations periods, yet a simple second will forever be tied to Earth and Sun.
I would definitely give my 'best web page 2019' to it. Bravo!
I remember spending a lot of time playing with a planets-and-gravity simulator on the Mac when i was a kid. I wrote a crappy clone of it as an applet for one of my first jobs!
This is the best web-based equivalent i found with a quick search:
I played with a simple program like that for the Amiga when I was younger, and then I discovered that there was an O(n log n) algorithm[1] rather than the obvious O(n^2) one. Never was up to writing a program to use it.
What a beautiful, well designed and informative explanation of the complex earth / sun relationship. Well done!
One thing I would love to see is the path of the sun across the sky for different times of year, and different locations on earth.
Here in Seattle, the difference is fairly dramatic between winter and summer, and I've come to realize that the sun is never directly overhead, not even in summer. It would be interesting to see the difference between polar regions vs in the tropics also.
Very much agreed. Things get weirder and weirder as you get towards the poles. At the poles themselves the sun spends half the year hidden, and the other half spiraling up and then down! But never gets very high above the horizon.
I've been thinking a lot about this lately and was thinking of making some educational YouTube videos about it!
Perhaps you are aware, but it is very simple to calculate.
(90-your latitude) + tilt of the earth (23.5 degrees) = maximum height of the sun during the year
(90-your latitude) - tilt of the earth (23.5 degrees) = minimum height of the sun during the year.
Effectively this means if your latitude is 23.5 or less, you get the sun directly overhead at some time during the year. If your latitude is above 67.5, you get polar night as the sun doesn't rise above the horizon (short one at 67.5, but as you go further toward the pole ever longer)
For Seattle, (90-47)+23.5=66.5 maximum. (90-47)-23.5=19.5 minimum.
Calling these the "maximum height" and the "minimum height" of the sun during the year makes it sound like the height of the sun will always lie between those two figures. That can't be the case -- they have night in the tropics too. Are these what I might call the "high maximum height", the yearly maximum of the maximum height of the sun on any given day, and the "low maximum height", the yearly minimum of the daily maximum height of the sun?
Yes, you are correct. My phrasing was unclear, especially in terms of "minimum".
The numbers are for the highest angle of Sun toward the horizon in a single day. This happens at solar noon (solar noon is the moment that Sun passes your local meridian/north south line).
At my school we had this weird climbing frame called the "Pipehenge". I climbed on it for years before we eventually did a class on it and learned that it was an astronomic map: https://www.youtube.com/watch?v=BM4d02tjTqk
SunCalc (http://suncalc.net) has a visualization for sun position throughout the year and time of day. Another great app is Sun Surveyor for Android, which gives an augmented reality view of the sun's position and trajectory.
> The Earth rotates around its axis from west to east, or, when seen from above, counter-clockwise.
North is not up.
When seen from above the South Pole, the Earth is rotating clockwise.
But really doesn't make much sense to talk about the rotation of a sphere by analogy to a 2D clockface. The Earth rotates from West to East; that's all that needed to be said here.
> Your just using your preferred frame of reference.
No I am not. What I said was that they should have left it as just that the Earth rotates from West to East (no frame of reference). I only talked about how it would look like from above the South Pole to show that the described anti-clockwise direction of motion was relative to the frame of reference that was being, unnecessarily, assumed.
The Earth has two poles and they are equal, just like with any (approximate) sphere. If you are going to describe how the Earth's rotation looks from above one pole then you should also describe how it looks from above the other. But once you describe it from both poles it becomes obvious that you're not really imparting any useful information because, while it looks clockwise from above one pole it looks anti-clockwise from above the other. Better to not use any frame of reference at all. We know that the sun rises in the East and sets in the West. With just a little thought it is then obvious that the Earth is rotating from West to East and that is all that needs to be said.
Frankly, it's pathetic that you play games with the words I use - 'hanging', 'rises' - which everyone understands are not actual descriptions of reality and don't engage with the argument at all, which is about reality.
You remain blind to, either willfully or unconsciously, my argument. Instead you come back with puerile rejoinders.
Look at the original quote from the article - "when seen from above". There was an assumption there that seen from above means seen from above the North Pole. Thus an assumed frame of reference when none was needed.
I do not assume seeing the Earth from above means seeing it from above the North Pole. Neither would an astronaut, who don't have to assume, they live the experience of seeing the Earth from all orientations.
The international date line is needed when you use local times instead of UTC, because the local date is incremented on midnight local time. So, if it's October 19 just after your local midnight, every timezone to the east should also have October 19, while every timezone to the west should still have October 18 because they haven't had local midnight yet. But that doesn't work, since east ultimately meets west when you track both directions far enough. So by convention we have defined a line (or rather a crooked boundary between timezones) where the date jumps back a day in the calendar when you pass over it in an eastwards direction.
I used it on an iPad.
For me, this was a beautiful example of how to leverage the strengths of a touchscreen to present information.
(too often, I find myself shaking my fist at how we’ve "bolted" a magazine onto a high-dpi display)
Wonderful stuff... thank you for making and sharing!
This is a personal reflection on the way it's presented. I'm sure that there are people who already know some of the content, and I found myself skimming over things, nodding, and thinking "Nothing new here." Then realised that there was something I missed, or an explanation that was especially nice, and I had to go back and re-read, wondering what else I might have missed.
So I found it all very smooth, clean, informative, but there was no story, no arc, no narrative, nothing to make me want to sit with a coffee (or other beverage of choice) and simply read like a novel. There wasn't the "Hook; Narrative; Reveal" structure that keeps the reader involved.
Which is a bit of a shame, because the bits I did take time over are really, really nice.
64 comments
[ 3.4 ms ] story [ 150 ms ] threadAn often used algorithm for the calculation of the apparent sun position (given a date and latitude/longitude of the observer) is SPA of Reda et al. [1]. If you're interested, I wrote an Android app (Sun Locator [2]) that implemented this algorithm.
[1] https://www.sciencedirect.com/science/article/abs/pii/S00380...
[2] https://play.google.com/store/apps/details?id=com.genewarrio...
Quote: One day we’ll colonize other planets, those planets will have different suns, orbits, and rotations periods, yet a simple second will forever be tied to Earth and Sun.
I would definitely give my 'best web page 2019' to it. Bravo!
This is the best web-based equivalent i found with a quick search:
https://hermann.is/gravity/
And this is a rather fine tutorial on writing your own:
https://css-tricks.com/creating-your-own-gravity-and-space-s...
https://en.wikipedia.org/wiki/Barnes%E2%80%93Hut_simulation
One thing I would love to see is the path of the sun across the sky for different times of year, and different locations on earth.
Here in Seattle, the difference is fairly dramatic between winter and summer, and I've come to realize that the sun is never directly overhead, not even in summer. It would be interesting to see the difference between polar regions vs in the tropics also.
I've been thinking a lot about this lately and was thinking of making some educational YouTube videos about it!
(90-your latitude) + tilt of the earth (23.5 degrees) = maximum height of the sun during the year
(90-your latitude) - tilt of the earth (23.5 degrees) = minimum height of the sun during the year.
Effectively this means if your latitude is 23.5 or less, you get the sun directly overhead at some time during the year. If your latitude is above 67.5, you get polar night as the sun doesn't rise above the horizon (short one at 67.5, but as you go further toward the pole ever longer)
For Seattle, (90-47)+23.5=66.5 maximum. (90-47)-23.5=19.5 minimum.
The numbers are for the highest angle of Sun toward the horizon in a single day. This happens at solar noon (solar noon is the moment that Sun passes your local meridian/north south line).
It's only ever directly overhead in the tropics.
Earth's mean obliquity is currently 23°26′12.2″ (or 23.43672°) and decreasing.
https://en.wikipedia.org/wiki/Axial_tilt
[0] http://stellarium.org/
North is not up.
When seen from above the South Pole, the Earth is rotating clockwise.
But really doesn't make much sense to talk about the rotation of a sphere by analogy to a 2D clockface. The Earth rotates from West to East; that's all that needed to be said here.
(But yes, there are many maps that don't have north at the top).
It seems reasonable to call north up because that frame of reference is how maps usually look.
To subsume your frame of reference, we could say the Earth isn’t hanging in space, it’s in free fall around the sun.
There are other frames of reference at progressively larger scales.
Edit: Also, the word ‘hanging’ usually implies an ‘up’.
No I am not. What I said was that they should have left it as just that the Earth rotates from West to East (no frame of reference). I only talked about how it would look like from above the South Pole to show that the described anti-clockwise direction of motion was relative to the frame of reference that was being, unnecessarily, assumed.
The Earth has two poles and they are equal, just like with any (approximate) sphere. If you are going to describe how the Earth's rotation looks from above one pole then you should also describe how it looks from above the other. But once you describe it from both poles it becomes obvious that you're not really imparting any useful information because, while it looks clockwise from above one pole it looks anti-clockwise from above the other. Better to not use any frame of reference at all. We know that the sun rises in the East and sets in the West. With just a little thought it is then obvious that the Earth is rotating from West to East and that is all that needs to be said.
Ok
> We know that the sun rises in the East and sets in the West.
You didn’t even try!
> North is not up
Look at the original quote from the article - "when seen from above". There was an assumption there that seen from above means seen from above the North Pole. Thus an assumed frame of reference when none was needed.
I do not assume seeing the Earth from above means seeing it from above the North Pole. Neither would an astronaut, who don't have to assume, they live the experience of seeing the Earth from all orientations.
Wonderful stuff... thank you for making and sharing!
This is a personal reflection on the way it's presented. I'm sure that there are people who already know some of the content, and I found myself skimming over things, nodding, and thinking "Nothing new here." Then realised that there was something I missed, or an explanation that was especially nice, and I had to go back and re-read, wondering what else I might have missed.
So I found it all very smooth, clean, informative, but there was no story, no arc, no narrative, nothing to make me want to sit with a coffee (or other beverage of choice) and simply read like a novel. There wasn't the "Hook; Narrative; Reveal" structure that keeps the reader involved.
Which is a bit of a shame, because the bits I did take time over are really, really nice.
It's really nice.