June Solstice

The sky, sodden gray in color, hangs low over the ocean. It’s winter down here. Frigid waves break against a beach empty of all the summer beach goers. The sun, a hazy blur behind clouds, makes a low arc across the northern sky.

It’s cold in the mornings too. Not Colorado-middle-of-winter-cold, but at least cold for us here on the North Island of New Zealand. With no real heat in the house, we sleep with our sleeping bags next to the bed and drag them over ourselves on particularly cold nights. Matthew, my son, still sleeps downstairs with the window open. He wants to live in Alaska someday. In the mornings when I awake, I prowl around in my sweat pants and down jacket while the coffee brews.

Today is the June Solstice (June 22nd this year), called the Summer Solstice in the Northern Hemisphere, but the Winter Solstice for us down here in the Southern Hemisphere.

If you remember from science class, solstices are when the Earth is most tilted toward or away from the sun, in this case, away from the sun for us here in New Zealand. Or in more precise celestial terms, the June Solstice is when the sun reaches a peak declination of +23.45 degrees from the celestial equator.

Celestial equator? Declination of the sun? For those of you who may not remember exactly what’s going on, here’s how it works.

The celestial coordinate system is exactly like latitude and longitude on the surface of the Earth—except out in space. The latitude equivalent on the celestial coordinate system is called declination.

Imagine the Earth’s equator extending directly out into space. That is the celestial equator, the imaginary plane extending outward into space from around the equatorial center of the Earth. Any stars or space objects located on that plane are on the celestial equator, and have a declination of zero degrees, just as locations on the Earth directly on the equator have a latitude of zero degrees. Stars above the celestial equator have a positive declination, and stars below the celestial equator have a negative declination. The declination of stars doesn’t change, just as the latitudes of locations on the Earth don’t change. In fact, declination is part of the system used by astronomers to convey the locations of stars and other heavenly bodies in space, so that anyone anywhere can find the exact location of objects in space.

As you know, the Earth revolves around the Sun, but in celestial terms it is often easier to think of the Sun revolving around the Earth. Let’s take a look at the Sun’s so-called path around the Earth each year. The Sun doesn’t follow the celestial equator around the Earth, rather it goes above and below the celestial equator (this corresponds to the tilting of the Earth’s axis) crossing the actual celestial equator on two occasions each year. In March at the Vernal Equinox, the sun is directly on the celestial equator, and hence the Sun at this point has a declination of zero degrees. At this point there are essentially equal hours of day and night everywhere on Earth.

Then as it becomes autumn in the Southern Hemisphere, the Sun travels upward above the celestial equator, that is, its declination becomes more positive. The Sun is tilted away from the Southern Hemisphere. Days get shorter. Each day as autumn proceeds, the declination of the Sun increases until on June 22nd it reaches a maximum declination of + 23.45 degrees off the celestial equator.

This is the June Solstice where we are now. The word ‘solstice’ actually comes from the Latin word, solsitium, which means “sun stands still.” Then after the solstice the Sun starts its journey back toward the celestial equator. The Sun’s declination then decreases until on or close to September 21st (September Equinox), the Sun once again reaches the celestial equator, and its declination is once again zero degrees.

From here, as it becomes spring in the Southern Hemisphere, the Sun arcs below the celestial equator, that is, its declination now starts to becomes negative. On December 21, it reaches a maximum of – 23.45 degrees declination, the first day of summer here, and the longest day of the year.

Then once again the Sun makes its way back toward the celestial equator, arriving in March back where it started for us, with its declination once again being zero degrees.

(1)

Except, of course, the Winter solstice on the image is our Summer solstice in New Zealand (1)

As you know, we feel the effects of this change in declination of the Sun or tilting of the Earth’s surface. They’re called the seasons. Without the seasons, the weather on the Fourth of July might be the same as on Christmas—not much fun.

With the change in the tilt of the Earth (change in the Sun’s declination), in the winter here, the Sun describes a lower arc across the northern sky. On the equinoxes, the Sun rises directly in the east, and sets directly in the west. But as it becomes winter here, it rises farther to the north of east and sets farther to the north of west. In fact, today on the solstice, the sun will rise at a compass direction of 61 degrees, almost 30 degrees north of east and will set at 299 degrees, again almost 30 degrees north of west. There will be 9 hours 33 minutes of daylight compared to 14 hours 46 minutes of daylight on the December Solstice.

The Sun also won’t get very high in the sky today. It will only reach a maximum elevation (zenith) of 29 degrees in the sky today compared to a maximum elevation of around 76 degrees in December.

What does all this mean? Ancient people used to time such things as the planting and harvesting of crops with patterns of the sun and the stars. But for most of us, along with being interesting, the solstices represent turning points in the year, almost like Wednesday, hump day, is for the work week.

The June Solstice means the Sun should now start to make its slow wayward path back toward longer days and warmer weather, at least for us here in the Southern Hemisphere. Or at least the Sun always has before.

Growing up and living in the Northern Hemisphere, as a kid there was always something bittersweet about the June Solstice. The whole wonderful summer would still be stretching out in front of me, but the solstice was always a harbinger of what was to come, that despite it being summer, that despite it being hot and the days stretching long into the night, the solstice meant that winter, although hidden and seemingly far distant, was inevitably and relentlessly on its way to return. I wouldn’t think about these things for long, often only for an instant, before getting back to playing or whatever else I was doing. But it was there, like a grim reminder that things always change, and now as I’ve grown older, I recognize there are cycles to all things in life.

 

 

‪1) Orbits and the Ecliptic Plane
ef.engr.utk.edu314 × 383Search by image

Advertisements

2 thoughts on “June Solstice

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s