Hike #3: Perihelion

When

Saturday, 2015-01-03

Where

Lookout Mountain, 16th St Trailhead

Duration

½ hour

Notable

Hiking in the middle of the day with no water and no sunscreen—won't be able to get away with that in a few months.

Today's hike was a quick out-and-back up and down Lookout Mountain, which is the mountain north of North Mountain. A few years ago on Lookout there was a large beehive obstructing the trail near the summit and if you got close enough you could observe the ceaseless activity of thousands of worker bees. Today the only buzzing to be heard was from an electric remote-controlled helicopter a man was flying at the bottom of the mountain.

Today is the perihelion. That's the yearly moment when the Earth is closest to the Sun. This year the moment happens about a half hour before midnight Arizona Time, so anyone a timezone or more to the east observes the perihelion during the next calendar day, Sunday.

The perihelion is also the moment when the Earth travels fastest through space relative to the Sun. The fact that the Earth speeds up and slows down during its elliptical orbit causes several asymmetries in astronomy and timekeeping.

• The northern hemisphere's summer season lasts longer than its winter season because the Earth moves faster around the sun during the winter, which means…

• The northern hemisphere receives more sunlight than the southern hemisphere.

• The month with the fewest days is February, a winter month in the northern hemisphere, whereas the two consecutive months with the full thirty-one days are July and August, both summer months.

• In the northern hemisphere, the earliest sunset happens before the shortest day of the year and the latest sunrise happens after. By how much earlier or later these days occur depends on the latitude of the observer. In Phoenix we have a few days to go till the latest sunrise, but cities far enough to the north, such as Seattle, may observe the latest sunrise as early as December.