What Heats a Fall Fence During Sunlight?

Fall

• Fall, also frequently called autumn, is the season between summer and winter, usually considered to cover the months of September, October and November. Fall does have a scientific definition: It is between Sept. 23 each year, the autumnal equinox, and Dec. 22, the winter solstice. That said, explaining to people in Alaska that it is still autumn in the third week of December, when snow has been on the ground for a number of months, may not be greeted with much enthusiasm.

North-South Considerations

• In the Northern Hemisphere, the sun moves further south toward the equator through fall. This is why northern climates are colder than southern ones in the winter. The difference is entirely noticeable to the human eye; sunsets that occur to the west-northwest in summer occur to the southwest in winter. This happens because the Earth does not rotate around a north-south axis; it is tilted at 23.5 degrees, and as the rotation changes, so does the apparent position of the sun in the sky.

  For this reason, the south side of a fence running east-to-west will be warmer than the north side in fall.

East-West Considerations

• No matter what time of the year it is, the sun rises toward the East and sets toward the West. The exact time of the day when the sun’s rays are strongest depends upon whether the measurement is taken before or after daylight-saving time takes effect. The zones used to modify what time of the day it is across large land masses largely even out the differences between places on the East Coast of a continent and places on the West Coast. That said, the maximum amount of heat delivered to the east of a time zone will be earlier than that to the west of the same zone. The most heat is delivered when the sun is directly overhead, which is typically between midday and 1 p.m. during the summer, getting a little later in the afternoon as fall progresses.

  For this reason, the east side of a fence will be warmer before the time when the sun is directly overhead, and the west side will be warmer afterward. This is true at all times of the year.

Heat From the Sun

• Sunlight feels hot because of the ultraviolet frequencies it contains; sunlight is a form of radiation. In the fall, the ultraviolet rays have to travel through more atmosphere to reach the surface of the Earth, which dilutes their impact.