In different regions, the sun is directly overhead at different times of the year. When do these event happen?
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4$\begingroup$ Possible duplicate of this question, the answer to which applies here. $\endgroup$– FredCommented Nov 6, 2016 at 6:24
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$\begingroup$ @Fred not quite a duplicate, but the answers are mostly the same. $\endgroup$– GimelistCommented Nov 6, 2016 at 7:07
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2$\begingroup$ Hello, and welcome to Stack Exchange. No time to answer, but a quick tip: look up analemma. $\endgroup$– Daniel GriscomCommented Nov 6, 2016 at 12:02
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2$\begingroup$ on this site you will find the information about this and more,just input where you are and you will find it timeanddate.com $\endgroup$– trond hansenCommented Jan 29, 2018 at 5:29
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3$\begingroup$ Possible duplicate of Sun's Highest Point on June 21 $\endgroup$– SpencerCommented Jan 30, 2018 at 0:55
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1 Answer
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Having the sun directly overhead can happen only between the Cancer and Capricorn tropics. That is, only the places between 23.5° of latitude north and 23.5° of latitude south.
- On the Cancer tropic (23.5° latitude north) it will happen once every year, on the day of the northern hemisphere solstice (about June 21st).
- On the Capricorn tropic (23.5° latitude south) it will happen once every year, on the day of the southern hemisphere solstice (about December 21st).
- On the equator it happen twice every year. One on each equinox (about March 21st and September 21st).
- For any other given place between the tropics, it will also happen twice every year. On the days when the Declination of the sun (a coordinate in the sky analogous to latitude on the Earth), matches the latitude of the place. Various formulas to calculate the declination to various precision can be found at Wikipedia.
This figure would help to visualize the situation:
The configuration depicted, will happen on the southern hemisphere summer solstice (about December 21st): The only day of the year when the sun passes exactly overhead on the Tropic of Capricorn.
When it comes to what time of the day it will happen, it won't happen at local noon (see this question), the exact time requires a lengthy calculation (see this), but a good estimate would be:
GMT - TimeZone + Longitude/15
Where GMT is Greenwich Meridian Time (the same than Universal Time for this effects), TimeZone is the time zone you are at. For instance -7 for the Pacific Time Zone in North America. And Longitude, is the longitude of the observer (expressed as a positive value for East longitudes and a negative value for West ones). The error of this estimate can be in the order of 15-20 minutes.
answered Jan 29, 2018 at 5:13
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1$\begingroup$ @farrenthorpe I'm pretty confident on this answer (I've expanded it a bit to explicitly cover the equator). In the same way that only one parallel of latitude pases by each point on Earth. Only one "parallel" of declination pass by one point in a observer's sky. That's is the case for the zenith (the point exactly overhead). Therefore, for a celestial object to pass by the zenith, its declination must be the same as the declination of the zenith. And the Sun have declination 0° only twice a year, on the equinoxes. $\endgroup$ Commented Jan 29, 2018 at 22:20
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1$\begingroup$ @farrenthorpe I do disagree. A reference would be appreciated. $\endgroup$ Commented Jan 29, 2018 at 23:05
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1$\begingroup$ @farrenthorpe That doesn't support what you say. It says "The sun always rises NEARLY perpendicular to the horizon" and then "The path of the Sun lies entirely in the northern half of the sky for the period from the March Equinox to the September Equinox and is entirely in the southern half of the sky from the September Equinox to the March Equinox, with the Sun passing directly overhead at noon on the equinoxes.". So it supports that the sun pass directly overhead only on the equinoxes $\endgroup$ Commented Jan 29, 2018 at 23:09
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1$\begingroup$ @farrenthorpe I've edited the answer to make it more clear. $\endgroup$ Commented Jan 29, 2018 at 23:16
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1$\begingroup$ @Pere please see my last comment which clears up my mixed-up comments and the point I was trying to make to Camilo $\endgroup$– f.thorpe ♦Commented Jan 29, 2018 at 23:16