Sky Matters: Spring equinox to bring sun's warming rays

THE winter has been unseasonably kind to us so far and with each passing day the Sun rises higher in the sky and warms the northern hemisphere that little bit more.

On March 20, at 21:58 to be precise, the Sun will appear to be directly over the Earth’s equator and the day and night will be of equal length.

We are all familiar with this being referred to as the spring or vernal equinox.

Possibly less familiar to us is just how much extra warmth the Sun brings to our shores on March 20 compared to the winter solstice on December 21.

In fact the Sun delivers three times more warmth (and light) to the Earth at the spring equinox compared to the winter solstice.

And it does this for 4.5 hours longer too, so the net effect is significant.

Plants, which rely on both light and heat from the Sun to grow and thrive, have clearly figured this out some time ago and so it comes as no surprise that we generally find them bursting into life around this time.

Of course other factors influence plant behaviour, including the air/soil temperature, since the chlorophyll molecule which enables them to convert light into energy for growth works more efficiently as the temperature increases.

But there’s no denying the critical role played by the Sun’s warming rays.

If the Earth was closer to, or farther from the Sun, the amount of warming we received could result in a cooler or warmer planet.

The same would be true if the Sun itself were to warm or cool. This may have happened as recently as four hundred years ago.

From 1500-1850 the northern hemisphere experienced a mini ice age and in the middle of this period (from 1645-1715) the number of sunspots visible on the surface of the Sun dropped precipitously.

Sunspots are regions of heightened activity on the sun (although somewhat bizarrely they appear as dark spots rather than bright ones).

Their absence may indicate that the sun itself had cooled a little, causing this mini ice age.

While not proven, it is an intriguing and credible hypothesis. This period of reduced sunspot activity is referred to as the Maunder Minimum and during this time the Thames river froze.

During the winters of 1683, 1716, 1739, 1789 and 1814 the freezing was so significant that it was possible to hold fairs on the river surface.

The evening after the spring equinox, March 21, we have the third and last supermoon of 2019.

In keeping with the warming theme, the native American tribes referred to a full Moon around the time of the spring equinox as the Full Worm Moon because earthworms could take advantage of the softening ground and do their magic with the soil again after their winter slowdown.

The Moon itself plays no significant role in warming the soil as it only reflects a few percent of the Sun’s light, but a full Moon is always an awe-inspiring sight whether it’s a supermoon or not.

It’s also not too late to see the planets Venus and Jupiter in the morning sky.

Venus is the brightest point of light to the east before dawn and Jupiter, though fainter, can be seen to its upper right as the next brightest object.

There are no well-known meteor showers in March, but you never know when a random meteor will streak across the sky and they really are a beautiful sight.

A dark location is ideal, and with the new moon occurring on March 6 (meaning it will not be visible at all throughout the night) the few days around the beginning on the month are the best times to give it a go.

Dr. Niall Smith is Head of Research at CIT and Head of the CIT Blackrock Castle Observatory

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