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Spring Movements North

© N. Lou Lyons

Our planet is in constant motion. Ice thaws and water rushes. Birds migrate to new grounds. Sap runs, trees sprout buds, and green plants shoot out of the soil. All the while, the earth spins over 1000 miles per hour at the equator. Geographic latitude determines the exact velocity of rotation. The movement is a mere 800 miles per hour in areas of Pennsylvania.¹ We move right along with the rest of the world so the speed goes unnoticed.

If we slow down and watch a sunrise or set it is possible to witness a small portion of this motion. Once each day, or every 24 hours, the world turns on its imaginary axis. The sun appears to float across the horizon. Night falls and day breaks as the earth rotates.

The world also orbits around the sun at a speed of 18.5 miles per second.² It still takes one entire year, or 365 days for the earth to make a full revolution. As the earth orbits the sun it is tilted 23.5 degrees on an imaginary axis. It is the tilted earth, in conjunction with the orbit that brings us changes in seasons.

Spring officially begins on March 20th. This is the date of the vernal equinox, which means “spring” and “equal night.” On that date the sun crosses the celestial equator - the area of sky seen above when directly at the equator. Sometime near the date of the vernal equinox locations around the world have equal hours between sunrise and sunset. Look for that date in your town here.

In Pennsylvania, the day closest to this phenomenon is March 17th, but spring officially begins when the sun crosses the celestial equator from south to north. More precise calculations and scientific terms like refraction play an important role in the details of this, but let it suffice to say, spring is on the way.

After the vernal equinox, the sun begins to point away from the Southern Hemisphere and more toward the Northern Hemisphere. Hours of daylight continue to increase for us. That additional heat warms the earth and raises temperatures enough to create dramatic changes in our environment.

Astronomers look to the skies but phenologists are interested in nature’s response to seasonal changes here on earth. You don’t have to be a scientist to research, study and know something about phenology. Many of us already take an active interest in climatic changes and how they affect our environment. Spring is one of the most anticipated seasons for phenology because it is the time of migration and growth.

The copyright of the article Spring Movements North in Pennsylvania is owned by N. Lou Lyons. Permission to republish Spring Movements North in print or online must be granted by the author in writing.