Vernal Equinox means its springtime
[The following is an open letter to Greater New Milford-area residents from the volunteers at the McCarthy Observatory on the campus of New Milford High School.]
Dear friends of the McCarthy Observatory:
Spring has sprung!
Well, technically anyway. We taught our adult education class last week to a stout-hearted group who endured seriously cold and a biting raw wind... in April.
And this author left Virginia after scraping thick frost off of his car. So spring warmth does not always relate exactly to the astronomical notion of "spring."
We call spring the time of the "Vernal Equinox," when the sun's path through our sky crosses the equator in its journey north. At that time. both the northern and southern hemispheres have equal day and night -- twelve hours of sunshine and nighttime.
So if you were on a beach at the equator watching the sun rise, traverse the sky and set, it would travel from due east to due west, and be directly overhead at noon. A pole pointed upward next to you would cast no shadow at exactly noon.
We celebrate, of course, because it is a great transitional event, a time of renewal... planting seasons and preparation for warmer days ahead have been celebrated since ancient times.
And we know the days will get even longer than 12 hours, eventually causing all the wonderful things of summer.
But, if you are in Sydney, or Capetown, or Santiago, how is that Vernal Equinox thing working out for you? It is called Vernal, meaning spring, but is the start of their fall, and their days are getting shorter, and the weather is going to be colder.
So why isn't it the Autumnal Equinox there? Because northern hemisphere civilizations named it, long before they had any idea of these annoying details.
So they can celebrate spring at the Autumnal Equinox if they so desire.
Of course this whole season and equinox and solstice phenomenon is cause by one simple fact -- somewhere around 4.5 billion years ago, as the solar system was forming, a large object hit earth and knocked its axis of rotation off kilter by 23.5 degrees.
This magic number of the earth revolving around the sun with its axis skewed by 23.5 degrees to the ecliptic plane of the solar system is the reason for our seasons, and the reasons for those things called the Tropics of Capricorn and Cancer, and the Antarctic and Arctic circles.
Get out the family globe, and you will see that each of those has a 23.5 degree dimension in its location. Dozens of apps for phones and tablets will let you simulate the whole thing.
So have faith. The weather will get warmer, and eventually we will have tulips. The 23.5 degree tilt is our friend.