Thursday, November 04, 2004

Science word of the day

perihelion -- noun. This is the point (or moment) in Earth's orbit when the we are closest to the Sun. Johannes Kepler realized that our orbit isn't circular, but elliptical instead. It's only slightly elliptical, so in the grand scheme of things, the difference between perhelion and its opposite, aphelion (when we are farthest from the Sun), is rather small: only some 5.1 million kilometers.

Distance from the Sun doesn't really have much to do with the seasons, contrary to what you might assume. In fact, perihelion occurs around January 4, and aphelion occurs around July 4.

The Wikipedia informs me that perihelion is a more specific term for the general idea of periapsis. That's probably more than even I wanted to know.

4 comments:

John said...

I'll remind you when perihelion comes around, just so you're prepared.

matt said...

indeed, it was the irregularities in mercury's perihelion that provided the first empirical confirmation of general relativity. rather than describing one ellipse, as per kepler, mercury orbits the sun in a series of roughly "concentric" ellipses that make a flower-like shape around the sun. perturbations were invoked to explain the deviation, but the predictions of general relativity accord best with experience. um, yeah.

John said...

Yeah! Like he said.

T.S. Nicarao said...

I read somewhere that other celestial bodies have their own names, too.
For ___, the closest/farthest orbit is:
Earth
perigee/apogee
Sun
perihelion/aphhelion
Star
periastron/apastron or apostron
Moon
perilune/apolune
Jupiter
perijove/apojove
black hole
perimelasma/apomelasma
anything
periapsis/apoapsis

Which is way more than we needed to know... :)