January 3 2018 marks Perihelion, and by coincidence it happens at nearly the latest possible sunrise at at 7:42 am local time (darkest morning) for our latitude of 45 degrees. (The official date of the latest sunrise for this area is January 2)
- After this day, for Canadians, the Sun rises earlier, and sets later as we move towards Spring Equinox.
- For Canadians at the most northerly latitudes, the latest sunrise doesn’t happen at all at this time of year, as the Sun remains below the local horizon. See Sunrise/Sunset times for Resolute Bay
- For latitudes close to 0 degrees, the amount of difference in time from one day to the next for sunrise or sunset is not as noticeable as the daily solar trajectory varies little due to the tilt of the earth . The tilt of the earth is of course the reason for the seasons.
- And of course, latitudes of the Southern Hemisphere are now passing Summer Solstice receiving more hours of sunlight as the Sun stays above the horizon longer. See See ChristChurch sunrise/sunset (Summer) times.
Analemmas Rise – snapshots in the East
As we learned last December, December Earliest Sunsets at Northern Latitudes, latest sunrise at our latitude from our ‘Sun Setting’ analemma happens before December 15. Similarly, near December solstice, the earliest sunset is determined by the ”Rising’ analemma which ‘snapshots’ the Sun each day at the same location at sunrise. Indeed, we have to locate the rising Sun in our picture right now at the latest sunrise to get all the points throughout the year! (In Resolute Bay, we don’t bother – at this time of year as there is no sunrise).
- The lowest point where the Sun rises in the East after December Solstice or sets in the West before December Solstice determines the date for earliest sunset and latest sunrise.
- Notice that the date for latest sunrise depends on our latitude location.
- The shortest day lies about midway between the dates of latest sunrise and earliest sunset.
Perihelion – Closest point in Earth’s Orbit happens in January – northern winter Solstice
- The dates for extreme points in Earth’s orbit, namely Perihelion (closest point to Sun in Earth’s orbit) and Aphelion(farthest point in Earth’s orbit) – do not depend on the observer’s location. So it is coincidental that at our latitude, the date for Perihelion Jan 3, nearly coincides with the date of latest sunrise Jan 2. After which, at our latitude, the days get longer ‘at both ends’ as the North Winter season finishes at Equinox.
From astronomical calculations, we also know that through time, thousands of years, the date for Perihelion changes. Currently Perihelion occurs 2 weeks after December solstice and Aphelion occurs 2 weeks after June solstice.
“The dates when Earth reaches the extreme points on its orbit are not fixed because of the variations in its eccentricity. In 1246, the December Solstice was on the same day as the Earth reached its Perihelion. Since then, the Perihelion and Aphelion dates have drifted by a day every 58 years. In the short-term, the dates can vary up to 2 days from one year to another. Mathematicians and astronomers estimate that in the year 6430, over 4000 years from now, the timing of the Perihelion and the March Equinox will coincide.” – courtesy Perihelion, Aphelion and the Solstices
As astronomical things to contemplate, here is a mere happy coincidence of dates ‘around’ the Sun. In early January, we celebrate our closest orbital approach and, in northern latitudes a return to earlier risings, of our nearest Star, Sol. Happy Perihelion — and Good Morning Starshine…