After a long winter, can you feel the energy rushing back through your body as the days get longer and the Sun warms up the northern hemisphere?
Even though here in Tenerife there is no real difference between seasons, days are a bit shorter and temperatures are a bit cooler in the winter (of course, up in the Teide National Park where we carry out our stargazing tours, it gets very cold at times!).
March 20th, however, marks what is known as the equinox and the beginning of spring. But what is the equinox, exactly?
The word comes from the Latin aequus and nox, which means equal night because it is the day where daytime and nighttime are approximately equal all over the Earth. The reason is that the Sun is vertical (or at the zenith) above the equator and, in addition, it rises directly east and sets directly west. Another way to put it, is that the axis of rotation of the Earth is 90º from the line connecting our planet and the Sun. This happens twice a year, around March 20th and September 23rd, and we will see later why it is an approximate date.
Contrary to what people might expect, daytime and nighttime are not exactly equal (12 hours each) because of atmospheric refraction and angular size of the Sun but, for general intents and purposes, they can be considered equal.
An interesting aspect is that equinoxes are the times where the length of daytime increases or decreases the fastest: in the northern hemisphere, at the spring (or vernal) equinox, daytime increases the fastest, whereas at the autumnal equinox it decreases the fastest. Of course, the opposite is true in the southern hemisphere!
By Tauʻolunga – Own work commons wikimedia
The equinoxes are the only times when the subsolar point is directly above the equator, so both hemispheres of the Earth are illuminated equally.
If you happen to be standing on the North Pole on the spring equinox, you would see the Sun rising again in the sky after months of darkness, whereas if you were at the South Pole you would be waving goodbye to it for about six months, and viceversa during the autumnal equinox. Pretty extreme, isn’t it?
Now, the exact date for the equinoxes changes slightly every year, and the reason is that the Gregorian calendar we use in modern times does not align perfectly with the Earth’s orbit around the Sun. The seasons start approximately at the same time only after a complete 400 leap-year cycle; this century, the earliest March equinox will be in 2096 on March 19th, and the latest was in 2003 on March 21st.
Now that nights are getting shorter until the solstice, is it still worth joining one of our stargazing tours? The short answer is: it surely is! Because we are located very close to the Tropic of Cancer, here in Tenerife we do not experience a dramatic change in the duration of the night between winter and summer so there are always plenty of hours of darkness to marvel at one of the darkest skies in the world throughout the year! Every month brings new constellations and celestial objects to look at, so you can book with confidence and you will experience the night sky like never before!
Written by Dani
