University of Wisconsin-Madison

Week 35 at the Pole

NSF/D. Larsen
NSF/D. Larsen

There’s the moon, but where’s the sun? It’s coming, it’s coming. At the South Pole, the sun rises only once a year (and it sets only once a year, too). But when the sun does rise—at the autumn equinox, approximately September 21—it doesn’t happen in a matter of hours, as it does for most of us each morning. Instead, the process is much more gradual, with daylight increasing little by little over the days and weeks prior to the actual appearance of the sun at the horizon. Either way, it’s twilight—or dawn, to distinguish it from dusk, the remaining glow in the sky that lingers after the sun sets. Twilight itself is defined according to the angle of the sun relative to the horizon, whether for sunrise or sunset. Did you know that there are three established subcategories of twilight?

The two photographs below were taken from about the same position at the South Pole roughly a week apart. The sun is definitely coming!

NSF/D. Larsen
NSF/D. Larsen
NSF/D. Larsen
NSF/D. Larsen