Talk:Subsolar point

Because of the tilt of the Earth on a axis

What is the subsolar point today?

You asked this question four years ago but I will answer. First, it is not meaningful to ask what the subsolar point is "today" because the subsolar point is constantly moving west around the Earth. The latitude of the subsolar point will change only a small amount over the course of a day, but the longitude is always changing a lot because of the Earth's rotation. So I assume the question you want to ask is "what is the subsolar point right now, or at an arbitrary date and time that I choose?" You can answer this with any number of free online astronomical calculators but the one I would recommend first is http://timeanddate.com/worldclock/sunearth.html. Clicking on that web page will show you a map of the world with the subsolar point (as well as the sublunar point) marked. Then you can scroll down to the heading "Position of the Sun" where it tells you the latitude and longitude of the subsolar point as well as some other data, and scrolling down further it gives you a list of cities or towns near the subsolar point ("Locations with the Sun near zenith").

Now let's say you wanted to know where the subsolar point will be at some point in the future (or where it was at some point in the past). For example, this Saturday, 31 December 2011, at 9:00 AM GMT. On the web page you scroll to the box marked "Change time and date" and then just use the drop-down menus. Make sure the time zone is the one you want (for my example, United Kingdom - England - London) and then click "Change time". Then it will show you a new map corresponding to the time you requested. You can see that at this moment the subsolar point is in southern Madagascar. Scrolling down, the page gives you the latitude/longitude as 23°07'S 45°25'E and, scrolling down even further, shows you that specifically the subsolar point at that time will be 513 km from Antananarivo. Also it gives you the local time in this locations; at 9 AM GMT it will be noon in Antananarivo. (Usually local clocks at the subsolar point will be within an hour or two of noon.) If you want a more detailed map, go to Google Maps and key in 23 7 S 45 25 E, then zoom in or zoom out as you like. —Mathew5000 (talk) 02:46, 26 December 2011 (UTC)

OK so the subsolar point moves in latitude and longitude. Got it! Now at (48N, 117W)the meridian transit for the sun is the subsolar point south of my position or because of light time is the point West of my longitude? The basic point is the subsolar point the actual geographic position of the sun in the sky or is it the apparent position (for me at 48N, 117W) just a few seconds west of my meridian. — Preceding unsigned comment added by Sunwukongmonkeygod (talk • contribs) 04:53, 6 May 2012 (UTC)

You asked,

"Is the subsolar point the actual geographic position of the sun in the sky or is it the apparent position (for me at 48N, 117W) just a few seconds west of my meridian?"

The subsolar point is a point on the surface of the Earth. As you know, it is constantly changing but at any instant there is one subsolar point on the Earth. The coordinates are absolute, not relative to your position.

For instance, suppose I'm in Oslo, Norway, at 8:30am on May 30. You're in Buenos Aires, Argentina (where it is 3:30am) and I ask you, where is the subsolar point. The answer is, at that moment the subsolar point is in India, at latitude 21°46'N, longitude 81°36'E. For someone who is at those coordinates, the sun will be directly overhead. (Note that if it's 8:30am in Oslo and 3:30am in Buenos Aires, it is noon in India. Generally speaking, for someone at the subsolar point, it will usually be close to noon local time; within an hour or two in any event.) Does that answer your question? Mathew5000 (talk) 03:26, 28 April 2014 (UTC)

The change in the latitude of subsolar point per day, which is due to Earth's revolution around the sun, is about 1.7 km, i.e. ~ 0.016 degrees = 0.98 minutes = 58.7 seconds. And, the term "subsolar point" can actually be said to refer to a particular latitude (which receives the sunlight at 90 degrees) rather than a point (which remains within 0.016 degrees of that latitude throughout a given day), hence the definition:

The subsolar point, or solar declination, is defined as the latitude where the sun is directly overhead at solar noon.

So, the position of the subsolar point moves to west on a given latitude, until it makes one complete round on that latitude, in a given day, and it makes a round trip between tropics in any year

85.110.88.44 (talk) 16:39, 22 December 2015 (UTC)

Formula for the Coordinates of the Subsolar Point?

Shouldn't there be a formula for the Subsolar Point for any given time? --Roland (talk) 09:49, 2 November 2019 (UTC)

Coordinates of the subsolar point

(I think this section should be added. In a sense, it is just numerically paraphrasing the original definition. The article is incomplete without it. It is an natural extension of the definition, but if you know of a published reference, please provide it. Alternatively, please correct whatever is wrong here. Thank you!)

In real applications, the coordinates, or the latitude and longitude, of the subsolar point for a given time, normally in GMT or UTC, need to be known. For instance, the coordinates can be used in relation to that of an observer to determine the solar zenith angle and the solar azimuth angle. The latitude of the subsolar point is simply the declination of the Sun for the given GMT, and the longitude of the subsolar point is equal to the hour angle at the prime meridian for the given GMT times -1, assuming the hour angle is 0 at solar noon, negative before the solar noon and positive after the solar noon. --Roland (talk) 05:56, 6 November 2019 (UTC)

@Roland Longbow: Please see WP:BURDEN. If material you're adding is being challenged, it's up to you to provide a source, not the editor(s) removing it. You start out by saying "In real applications, the coordinates ... of the subsolar point ... need to be known." Really? This is far from obvious. I (and probably most readers) have no idea what such applications are, or even if there are any at all. There are also plain problems with the exposition. For example, "... the given GMT ..." makes no grammatical sense, "the hour angle" is unclear, etc.

To recap, if you want to add this, it needs to be cleaned up, and you must provide a source. –Deacon Vorbis (carbon • videos) 16:50, 6 November 2019 (UTC)

I just added the section Coordinates of the subsolar point, this time with reference to a publication that just came out in the journal Renewable Energy. It uses the coordinates of the subsolar point to calculate the solar zenith angle and solar azimuth angle. Hopefully, it works out this time. --Roland (talk) 05:38, 11 April 2021 (UTC)

Map on the page needs Year Information

Because the subsolar point changes daily, it also changes annually. The map provided as a sample should declare the year as well. Khosrownia (talk) 16:54, 21 March 2024 (UTC)