One can view the heavens in Australia and beat the summer’s heat

On Tuesday, June 20, at 10:24 p.m. MDT, the sun reached its location in the sky that is farthest north of the celestial Equator.

The sun has been traveling northward against the background stars for the past six months, and has been north of the celestial Equator for the past three of those months; it will now commence traveling southward, slowly at first, then crossing the Equator three months from now and then being at its farthest south location three months later. After that, the cycle starts over again.

With the sun being at its farthest point north on Tuesday evening, we experienced more hours of daylight on the adjoining days than we will on any other day this year. If the Earth had no atmosphere, this would be the hottest day of the year at least, here in the northern hemisphere. Because of the atmosphere’s capacity to retain heat and radiate it away slowly, the coming three months will be hotter, in general, than the previous three months have been, despite the similar placings of the sun.

These next three months, then, are, in general, the warmest time of the year for those of us in the northern hemisphere, and collectively constitute the season of the year that we call summer. The specific point on Tuesday night when the sun was at its farthest point north is usually – and chauvinistically – called the summer solstice, although June solstice would be more accurate.

For many locations, including here in the deserts of the southwestern U.S. – and especially in locations to our west during the recent past – the daytimes can be uncomfortably warm during the summer, while the nights can be relatively pleasant. Summer evenings thus often provide a comfortable environment for sky-watching, although the fact that the true hours of darkness do not begin until quite late, detract from this a little bit.

One of the most distinct groupings of stars on these pleasant summer evenings is the constellation Scorpius, which rides prominently in our southern sky. Of all the recognized constellations, Scorpius is one of the few that easily resembles what it is supposed to represent, i.e., a scorpion – which seems to be standing on its tail – with a distinctive head formed by three bright stars on a north-south line, a body represented by a long line of bright stars extending southward and then curving eastward and back north, and culminating in a distinctive tail, with even a stinger. To the east of Scorpius, and thus at its highest a couple of hours later, is Sagittarius, which includes a grouping of bright stars that closely resembles a teapot.

To the north and east of Sagittarius, rising higher in our eastern sky, is a large triangle – the so-called Summer Triangle – made up of three bright stars, each of which signifies its own constellation. The westernmost of these is Vega in the constellation Lyra, to its east is Deneb in the constellation Cygnus, the swan, and to the south is Aquila in the constellation Aquila, the eagle.

From dark rural sites, a hazy band of light extends southward through these constellations into Sagittarius, where it appears thickest and brightest. This is what we call the Milky Way, and it is made up of the combined light of large multitudes of distant stars in what we call the disk of our galaxy. The center of our galaxy is within Sagittarius, which is why the Milky Way appears so bright and thick in that direction.

The days of summer can be so hot that it might cause one to think of our friends in the southern hemisphere; for them, the June solstice marks the beginning of the season of winter. Three times in his lifetime this author has found himself in the southern hemisphere at the time of the June solstice, and his older son, presently residing in Australia, is experiencing it now.

The June solstice sky scene from the southern hemisphere has both its similarities and its differences from what we experience here in the northern hemisphere. Scorpius, for example, is almost directly overhead, and perhaps because of the lack of a horizon to compare it to, doesn’t seem quite as imposing as it does when we see it in our southern sky. Sagittarius looks less like a teapot and more like a milk dipper with the teapot handle being the bowl of this milk dipper – this apparently being due to the different viewing perspective.

To the south and west of Scorpius is the constellation Centaurus, of which we can only see the norther most portions here; from the southern hemisphere, it is marked by two very bright stars known as Alpha and Beta Centauri the first, and brighter, of these being the closest star to our solar system. These two stars collectively are known as the pointers, since a line starting from Alpha and extending through Beta points to the Southern Cross. The north-south line of the Southern Cross itself points to the south celestial pole, although at present there is no bright star that marks that location unlike the north celestial pole, which is presently marked by the star Polaris.

The most dramatic sight in the southern solstice sky, however, is the Milky Way itself. When Sagittarius passes almost directly overhead – which it does around the midnight hours this time of year – the view is that of an edge-on galaxy, photos of which are in just about any astronomy book, pasted onto the entire vault of the heavens. This author remembers being almost completely blown away by this scene when he first witnessed it during his first visit to Australia over three decades ago.

It is a scene which he will hopefully witness again sometime in the not-too-distant future; after all, he has a son in the southern hemisphere who needs to be visited at some point.

But even the northern hemisphere’s solstice sky is well worth viewing on these pleasant summer nights.

Alan Hale is a professional astronomer who resides in Cloudcroft. Hale is involved in various space-related research and educational activities throughout New Mexico and elsewhere. His web site is http://www.earthriseinstitute.org.