Quadrantid meteor shower Jan. 2-3, 2013
Were you like me and got up this morning only to find the sky still overcast? No meteors for this poor astronomer. I hope some readers fared better.
It always seems to be clear over John Chumack’s home in Dayton, Ohio. Chumack, a long-time amateur astronomer, recorded 52 Quadrantid shower meteors overnight using a low-light video camera. Click the video above to watch it all go by in just 33 seconds.
At 10:37 p.m. January 1 this week, Earth passed an annual milestone in its orbit, reaching its closest point to the sun for the year. Astronomers call it perihelion, a Greek-rooted word combining ‘peri’ (close) and ‘helios’ (sun). Earth’s distance from the sun varies over the course of a year because our orbit is not a circle with the sun at the center. Rather it’s an ellipse – like all the other planets’ orbits – with the sun slightly off to one side.
On July 5 this year, Earth will reach its farthest distance from the sun called aphelion (AP-hee-lee-on). The difference from one side of our orbit to the other is only about 3 million miles or 3.3%. While the change in distance affects the amount of heat we receive from the sun, it’s not nearly enough to affect the seasons, which are caused by the 23.5 tilt of our planet’s axis. The tilt of the north pole toward the Sun in June causes summer north of the equator, while summer south of the equator comes six months later when the south pole is facing the Sun.
Because our distance from the sun varies, so does the sun’s size and our planet’s orbital speed. When closest to the sun, Earth moves faster than when farther away, the same way sun-hugging Mercury orbits faster than distant Jupiter. Our average speed is 18.5 miles per second (66,600 mph) through space, but today we’re zipping along 2,160 mph faster than we will come July. I can almost feel the wind in my thinning hair.
Giorgio Rizzarelli, a regular reader and commenter on this blog, performed an interesting experiment comparing the size of the sun at aphelion on July 5, 2012 and at perihelion earlier this week. The difference is immediately obvious from his unique perspective.
Giorgio went a step further and measured the difference in diameters to arrive at the Earth’s orbital eccentricity.
Eccentricity or ‘e’ refers to how stretched out a planet’s orbit is compared to a perfect circle. With a circle defined as e = 0, Rizzarelli calculated an ‘e’ of 0.017 (nearly circular but not quite) for Earth’s orbit, in excellent agreement with the published figure of 0.0167. (see calculation below). Amazing what you can do with a camera from your own backyard.
“The disc in lower photo is 3.4% bigger than in the upper, so (dividing by 2) 1.7% bigger than average. Hence Earth today is 1.7% closer to the Sun than average. This defines the approximately eccentricity, (which is) 1.7% or 0.017.” – Giorgio Rizzarelli