The significance of precession

Our ordinary, everyday calendar is based on a year that is measured from equinox to equinox and solstice to solstice. This is called the tropical year and it contains an average of 365.242 solar days. A solar day is the time the Earth takes to complete one rotation. Its average length is 86,400 seconds (= 24 hours). Measure the year from one perihelion to the next, however, and the length is slightly different: 365.259 mean solar days. This is about 25.13 minutes longer. It means that the equinoxes return more quickly than do successive perihelia. The difference is one solar day every 57.3 years. This is the precession of the equinoxes.

Why should it matter? At present, Earth is at perihelion in January and at aphelion in July. This timing moderates temperatures, warming the Northern Hemisphere in its winter and cooling the Southern Hemisphere in its summer. As the dates of the equinoxes return faster than Earth's arrival at perihelion and aphelion, however, this effect changes. Ten thousand years from now the dates will be the reverse of those of today. Earth will then be at perihelion in July and at aphelion in January. This timing will cool the Northern Hemisphere in its winter and warm the Southern Hemisphere in its summer. The seasonal temperatures will be more extreme than they are now.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

Get My Free Ebook

Post a comment