Happy #WeatherWednesday, weather peeps! It’s the first full day of summer in the Northern Hemisphere! Today’s topic of discussion is an explanation of the solstice. The summer solstice was at 11:24pm CDT (0424 UTC) last night. For our friends in the Southern Hemisphere, winter has started (brrr, maybe).
The shortest nights and longest days of the year occur this week. If you were to live north of the Arctic Circle, the midnight sun would be the highest in the sky. This is because of the position of the Earth in its orbit around the sun. Some people out there think the summer season owes its heat to a closer distance to the Sun than in the winter. This is false! The Earth is actually closest to the Sun in January during northern winter. Note: the average distance to the sun is 93 million miles; approximately 91.4mil in Jan. and 94.5mil in July.
So what about the position of the orbit makes the days longer and the direct Sun rays stronger (more thermal energy irradiated) in the summer? The tilt of our polar axis favors more of Northern Hemisphere to see the Sun than the Southern Hemisphere during the summer. Vice versa in the winter. The tilt is approximately 23.5°. Imagine a vertical line perpendicular to the orbital plane. The polar axis in which the Earth spins is at a 23.5° angle from this vertical line. The solstice is the point where the 23.5° plane is the most directed at or away from the Sun. See image below for guidance.
The solstice varies yearly between June 20-22 for summer and January 20-22 for winter. The Gregorian Calendar keeps track of the yearly shift in the solstice day. Despite the solstice occurring last night, the average hottest temperatures in the northern mid-latitudes are still about a month away due to thermal lag of the Earth. Don’t tell Phoenix and Las Vegas that, though. They’re basking in the record territory in the mid 110s-120s this week!