If you enjoyed the weekend weather, today promises to offer more of the same. It will be mostly sunny and cool with a high temperature in the mid-to-upper 60s. However, showers are expected by lunch tomorrow, and more showers are likely by Thursday and Friday. Daytime highs will reach the mid 70s by the end of the week. As you may know, we are into the last full week of Summer. The Autumnal Equinox happens Friday morning at 5:05 Eastern Daylight Time. That's when the direct rays of the Sun are above the Equator, technically marking "equal day and equal night" across the face of the globe. As the direct rays of the Sun continue to move South of the Equator, the Southern Hemisphere will be enjoying the start of Spring next week.
However, here in the Northern Hemisphere, the amount of daylight continues to dwindle, and the Sun now sets before 7 o'clock in the evening. Recall that in late June, during the time of the Summer Solstice, the Sun set at 8:30. We've lost over an hour-and-a-half of daylight just in the evening alone over the last three months.
So why does the Equinox happen? The seasons of the year are caused by the 23.5ยบ tilt of the Earth's axis. Because the Earth is rotating like a top, it points in a fixed direction continuously toward a point in space near the North Star. That's why the North Star appears to be the only star which doesn't move in our night sky. However, the Earth is also revolving around the Sun. During half of the year, the Southern Hemisphere is more exposed to the Sun than the Northern Hemisphere. During the rest of the year, the reverse is true.
At noontime in the Northern Hemisphere the Sun appears high in the sky during the Summer and low in the sky during Winter. It is highest at the Summer Solstice in late June and lowest at the Winter Solstice by the end of December. The half-way points in the year are called the Equinoxes. It is the time of the year when the Sun rises exactly in the East, travels through the sky for 12 hours, and sets exactly in the West. The photo below shows visitors at Stonehenge on the Salisbury Plain in England.
However, on the Autumnal Equinox in southwestern Connecticut, the Sun rises at 6:40 a.m. and sets at 6:50 p.m., giving us 12 hours and ten minutes of daylight. That has to do with the angle at which the Sun rises and sets. Actually, "equal day and equal night" occurs for us on September 25th and 26th when we receive just about 12 hours of daylight and 12 hours of darkness.
Take advantage of another nice day. Summer is on its way out, and Fall is just four days away. Today may very well be the best day of the week.
Paul
