In the first few minutes of January 3, universal time, Earth reached the closest point to the sun in its annual orbit. At that moment, the earth perihelion, you and I and our national parks were just 91,402,505 miles (147,098,074 km) from the sun.
The staff here at Traveler would like to be among the very first to wish you a joyous Perihelion Day. As you celebrate this very special occasion with the traditional greetings, gifting, and family gatherings, please remember to drink responsibly.
Postscript: All other things being equal, the sun's rays should pack a wee tiny bit more warming power today than they did yesterday. Can you feel it?
Comments
We've canceled our traditional Perihelion celebration due to the temperature being 3 degrees Fahrenheit this morning.
Good ol' Michigan. Three degrees keeps the riff-raff out. I'm living proof. But hey, it was 19 degrees here in Bubbaland when I got up this morning.
I wonder what affect the closer proximity has on the tides? And what if a leap tide coincided with it? Anyone have any ideas?
I'm no expert on this thing, but I've always assumed that, where the tides are concerned, lunar distance is vastly more important than solar distance. BTW, if you wait long enough (thousands of years), precession will have the perihelion occurring during the northern Hemisphere summer (contributing to greater heating) and the aphelion occurring during the northern hemisphere winter (contributing to greater cooling). Scientists believe that this helps to explain the onset and ending of ice ages.
FYI -- strength of tides depends on the gradient (or first derivative of force with respect to distance) of the gravitational field of the sun and moon, not the actual gravitational forces. Obviously the sun's gravitational force on Earth is much greater than the moon's -- that's why we're in orbit around the sun and not around the moon. However the gradients favor the moon over the sun by about a 2:1 ratio. Lunar and solar contributions to the tides align and combine at new and full moons for a strong "spring tide" (think 2 + 1) but they partially cancel out at 1st and last quarter for a weak "neap tide" (think 2 - 1). As to whether tides are stronger when sun or moon is closer, the answer is yes, the gradients of their gravitational fields would also be greater, but the difference is not very much. Earth's orbit is pretty close to circular -- 91 M miles from sun at perihelion, 94 M miles at aphelion -- so don't expect to notice this with unaided senses. However as posted above the effect when added and averaged over many years does lessen the severity of summer in the northern hemisphere and does worsen it in the southern hemisphere and has been invoked to help explain cycles of ice ages over tens of thousands of years.
I have long enjoyed wishing my friends a happy perihelion -- I guess I'm not ready for the holidays to be over and it's nice to have another excuse for well wishes.
Thanks for the explanation, David, and thanks for helping to nurture perihelion awareness. What we need is some sort of ritual. Got any ideas?