The change from bitter cold to warm sunshine and blooming flowers is usually a welcome phenomenon. There are many customs that surround this time of the year. People turn to the groundhog to find out how much longer winter lasts, and commence with planting new gardens. Many people check the weather anxiously to find out if the risk of freezing has passed before proceeding with garden activities. History, however, mandates a more complicated approach to declaring the beginning of the spring season. The next time you check on the official start date of spring, here is what is being calculated.
You probably have a little alert written on your calendar that states the first day of spring. This is always sometime between March 19th and March 21st. The first day of spring is not decided because of sudden sunny weather or that mischievous groundhog. The date varies due to the nature of the Earth’s orbit. The calendar year varies slightly because of this. The Earth has an orbit that is a bit varied from the perfect circle that we often imagine. This slight deviation from a perfect circle causes the number of days in a year to refrain from being even. Our relationship to the sun changes over time. Other planets exerts a gravitational pull on the Earth that contributes to these variations. Climate also responds to these differences. Climate changes may also have to do with the environment combined with the Earth’s position. All of these factors lead up to date determined to be the vernal equinox.
Equinoxes and Solstices
The date that an equinox falls on is labeled as the start date for the spring season, as well as the fall. A solstice has to do with the beginning of winter and summer. An equinox or solstice represents a specific modification in the yearly journey of earth around the sun. The coolest and warmest days of the year now happen about two days earlier than they did around 150 years ago. An equinox is a time when the sun goes over the equator. This results in a day and night that are almost exact in their length over the entire earth. The sun also hovers directly over the equator at noon, as well during both equinoxes.
The Earth’s Movement
Day and night occur because of the 24 hour rotation of the earth on its axis. The seasons happen because of a combination of a 23.5 degree tilt and the 365 day journey around the sun. Different areas around the earth experience varying lengths of sun exposure and darkness. The North Pole, for example, does not see the sun until the springtime. The sun rises slowly and does not fully reach its height until the summer solstice. The sun then begins its descent and sets when the fall equinox happens. This is usually around the end of September. The North Pole is completely dark for part of the year. The extreme of 24-hour light or dark is not the norm for other places, however, the lengths of the days do change as the earth rotates and tilts.
Days become short during the winter months because of the position of the Earth. This starts at the winter solstice and increases rapidly. It is common during the winter to find yourself driving home from work in total darkness, when during the spring you can get home and enjoy a walk before the sun sets. The summer solstice brings the longest day of the year to the Northern hemisphere.
Ancient civilizations were very in tune with the seasonal changes, as their livelihood depended on it. They had to know when to plant and store food for the coming seasons. Calendars have been documented as far back as the fourth century B.C. Found in the Americas, these calendars worked with the cycles of the sun. Specific buildings were constructed to pinpoint the equinoxes and solstices so that it was clear when to prepare crops. Many cultural activities revolved around these times.
In Australia there is an arrangement of stones that is thought to have been used to measure the cycles of the seasons. This calendar is circular, indicating the continuous return of each season, and is almost as precise as a modern day compass. It is off by only a fraction of a millimeter concerning the various points of a compass.
Artifacts from many cultures show an interest in measuring time. Bones and sticks have been found with marks in them, possibly representing the counting of time. The arrangement of Stonehenge is thought to be concerned with the changing seasons. It may have its roots in determination of solstices, eclipses, and other routine events. Early Egyptian calendars followed the cycles of the moon, and later made its way to a 365 day recording after observing certain stars. The Mayans made their calendars by adding the observation of the planet Venus to their calculations. They also used the sun and moon. Their calendars ended up being between 260 and 365 days long.
When you look up at the stars each night you are not looking at the same star you saw last season. Over time, the earth rotates in a way that exposes you to a different part of the sky. There is a small change in the timing of the setting of the stars each night. This adds up to about four minutes each evening. As the changes are seasonal, coinciding with the annual orbit around the sun, you see the same stars each summer, winter, spring, or fall.
The upper portion of the Earth is further from the sun when winter is happening. The heat received during the Earth at this time is about seven percent less than in the warmer months. When the Northern Hemisphere, however, experiences the longer days and more sun exposure, this balances things out. The heat may not be felt in its entirety, however, until later in the summer season. The oceans need to warm up first, before the heat is felt on land. There is still a lot of variation in the temperatures of different areas of the earth. Tropical climates do not experience the extreme seasonal changes of many continents. Geographical locations further from the equator are often known for harsh winters and mild summers. Land areas closer to the equator may be relatively warmer, even in the winter.
The beginning of spring is only a small portion of the entire calendar year and the Earth’s many changes in position. The seasons follow patterns that are easily marked by equinoxes and solstices. While the dates of these change slightly from year to year, they can be predicted regularly. Ancient civilizations were very in tune with the environment and its patterns. Working with nature in ancient times was the key to survival. Some ancient calendars come close to our current 365 day calendar. This is the most compelling evidence of the predictable patterns of the planet Earth, as well as the intelligence of ancient civilizations. Spring may indeed be on the way, and you can better know how to prepare by following our modern day calendars.