(from our friends at OMSI)
For the Pacific Time Zone, summer officially begins with the summer solstice on Wednesday, June 20 at 4:09 p.m. PDT. The earth is tilted so that the north pole is at its closest point with the sun. (Yet, the earth will be at its farthest distance from the sun, called aphelion, on July 5) As a result there will be more minutes of sunlight in the northern hemisphere than there are at any other time of the year. The word “solstice” is derived from the Latin sol-stitium, for sun-standing. The summer solstice is the time of the year when the sun stops its northern climb and stands briefly before turning back toward the equator. As seen from Portland, the sun will reach its highest northern point in the sky at 67.54 degrees from the horizon on June 21 at approximately 1:12 p.m. From March 21 until September 24, there are more hours of daylight than darkness. After June 21, the days will gradually grow shorter until December 21, the winter solstice.
Not everybody is celebrating. Far to our south, across the equator, winter has arrived. For people in the southern hemisphere, June 21st, will be the shortest day of the year. It also means the beginning of their winter.
Six months from now, when the earth has made half of its yearly trip around the sun, the northern hemisphere will experience that cold weather. December 21 will be winter solstice. That’s when we have the fewest hours of sunlight and winter officially begins.
Learn more about the reason for the seasons with this short video available from the NASA Explorer Schools Program: Reasons for the Seasons