Only two days short of full-moon phase, a waxing gibbous moon illuminates the evening sky after dusk on Independence Day, stealing just a bit of thunder from the fireworks displays. This and every July 4 (actually July 3 at 7 p.m. Pacific Daylight Time this particular year) is astronomically notable for the fact that it marks Earth's aphelion -- the time when our planet lies farthest from the sun (94.5 million miles.) In January, Earth is an almost insignificant three percent closer to the sun than it is now. On account of this minor irregularity, Northern Hemisphere summers tend to be slightly cooler than they otherwise would be. At the same time, the Southern Hemisphere, which experiences winter during our "summer" months, has winters that tend to be slightly cooler.
Only two days short of full-moon phase, a waxing gibbous moon illuminates the evening sky after dusk on Independence Day, stealing just a bit of thunder from the fireworks displays. This and every July 4 (actually July 3 at 7 p.m. Pacific Daylight Time this particular year) is astronomically notable for the fact that it marks Earth's aphelion -- the time when our planet lies farthest from the sun (94.5 million miles.) In January, Earth is an almost insignificant three percent closer to the sun than it is now. On account of this minor irregularity, Northern Hemisphere summers tend to be slightly cooler than they otherwise would be. At the same time, the Southern Hemisphere, which experiences winter during our "summer" months, has winters that tend to be slightly cooler.