pɛrɪˈhiːlɪən perihelion: that point in the orbit of a planet, comet or other body at which it is closest to the sun Not to be confused with the parhelion, which I wrote about last month. Today (4 January 2017), the Earth is at perihelion, its closest to the sun, a mere 98% of its average … Continue reading Perihelion: Part 1
Having recently criticized Tristan Gooley’s explanation of the tides, I felt obliged to try to do better myself. It’s a tricky job, and there are many partial and misleading explanations out there. So here goes. Tides happen to anything that is orbiting in a gravitational field. I’m going to hone down on the Earth in … Continue reading Tides
Clear skies here, chez Oikofuge, for Monday’s transit of Mercury, the first in almost ten years. Mercury and Venus are the two planets that orbit between Earth and the sun, so they are the only two planets that we can occasionally see passing in front of the sun. If you look at the orbits of … Continue reading Transit of Mercury
Here’s the problem: the tropical year, the time it takes the Earth to go through a complete cycle of seasons, is 365.2422 days long (to four-decimal accuracy). If every calendar year were 365 days long, then the missing 0.2422 days would add up from year to year, each year starting a little earlier relative to … Continue reading February 30th
Christmas Day’s full moon made me decide to make my first post of the New Year about a resolution—specifically, the resolution of the human eye. (See what I did, there?) We’re so used to images of the full moon like the one above, it’s difficult to remember that, until the invention of the telescope in … Continue reading New Year / Resolution