Sunday, June 21 is not only father’s day, but also the summer solstice — the longest daytime (and shortest nighttime) of the year, for the Northern Hemisphere. Two things to celebrate!

Few people know that the reason we have seasons — that the length of daylight varies throughout the year — is that billions of years ago, in the violent early days of our solar system, Earth got hit by a roving mini-planet. Like many accident victims, the Earth could not straighten out, and has orbited the Sun leaning to one side ever since. When our hemisphere leans into the Sun, we have the long days of summer; when our side leans out of the Sun, we have to contend with the short, cold days of winter. (Venus and Jupiter did not have this early experience, and they don’t have seasons. Mars, like us, does.)

Here in San Francisco, Sunday’s solstice will give us almost 15 hours of daylight.  A lot of time to groan at dad jokes!  But if you are a fan of the coming of summer, remember to give a thought of thanks to that ancient mini-planet and the accident it caused.

Extra Note: The Popular, but Wrong Reason for the Solstice:

• Many people think the seasons are caused by the Earth’s orbit not being a circle, but an ellipse, and that it’s summer when we are closer to the Sun in that ellipse
• But in 2025, the Earth was closest to the Sun on January 3^rd.
• Also, if distance were the reason, then Australia would have the same seasons as the U.S., instead of the opposite seasons (which is what we observe)