NYT Sky Watch: Week of June 28
Some people think our seasons are caused by the Earth’s changing distance from the Sun. But it is actually the 23.5 degree tilt of Earth’s axis that makes the Sun appear above the horizon for different lengths of time at different seasons. On Friday at 10pm Eastern time, the Earth will be at aphelion, its farthest point from the Sun in its orbit, a distance of 94,505,048 miles. Back on Jan. 4, Earth was at perihelion, closest to the Sun. The difference in distance was 3,104,109 miles, or 3.28 percent, which makes a difference in radiant heat received by the Earth of nearly 7 percent. It seems that for the Northern Hemisphere such a difference would tend to warm the winters and cool the summers. But the preponderance of large land masses in the Northern Hemisphere, which affects the amount of heat lost from the air, tends to make the winters colder and the summers hotter.
Joe Rao, Hayden Planetarium