Night Lights: Fall befalls us — Expanding darkness means growing stargazing

Photo courtesy of Andy Veh. Sundials used to be the method for calculating time of day.

Photo courtesy of Andy Veh. Sundials used to be the method for calculating time of day.

By Andy Veh, for the Redoubt Reporter

Now that it gets dark at a reasonable time in the evening, besides the sun and the moon we can again see planets, the occasional meteor, comets, stars, some star clusters and two galaxies.

First find the Big Dipper low in the northwest, then take the distance between the dipper’s last two stars and extend it five times toward the zenith (the point straight up) and you get to Polaris, the North Star, which is a semibright star at the end of the Little Dipper’s handle. It also marks our latitude on the Kenai Peninsula at 60 degrees above the northern horizon.

Next find the constellation Cassiopeia, in the shape of a W, on the other side of the Little Dipper, high in the northeast. High in the sky as well, almost in the zenith, is Cygnus the swan, which also looks like a cross. Its brightest star, Deneb, connects with two other bright stars, Vega and Altair in the constellations Lyra, the Harp, and Aquila, the Eagle. Together they make up the prominent Summer Triangle.

Just left of them is the Great Square of Pegasus, high in the southeast. Turning to the west we can see bright red Arcturus setting, a sign that summer is over. It can also be found by following the Big Dipper’s handle’s arc. And rising in the northeast is bright yellow Capella, a corner of Auriga’s pentagon.

Throughout the night, all constellations move from east to west (of course, it is Earth rotating that gives us this illusion), so the evening western constellations set while in the east Taurus, Orion, Gemini and Cancer are rising throughout the night, telling us that winter is coming up.

Three planets, Mercury, Saturn and Mars, set around the same time that the sun is setting and are therefore not visible. In the Lower 48 they actually are visible because at those latitudes the ecliptic (our sun’s apparent path through the sky) and the planets’ orbits make a steeper angle with the horizon, and Saturn and Mars would make a fine pair in the early evening.

Neptune and Uranus are nicely situated all night long and up to 25 degrees above the southern horizon in Aquarius and Pisces, respectively. Binoculars or a small telescope are needed. For good finder charts see www.skyandtelescope.com/astronomy-news/observing-news/uranus-and-neptune-in-2014/.

Jupiter and Venus are rising in the middle of the night, around 3 a.m., in the northeast. Toward the end of the month, Venus closes in on the sun and therefore gets harder to observe. As Earth continues to pass Jupiter throughout fall and winter, the giant planet seems to retreat more from the sun and appears higher in the sky. If you see one or two bright objects during the predawn hours when driving east on the Sterling Highway, it’s one of these two. The crescent moon joins Jupiter on Sept. 19 and 20, and Venus on Sept. 22.

My sister sent the accompanying photo from Germany, asking me what time it is on this sundial. (The photo was taken by her friend, Sanny Reiche, in early August on the side of a building of her former high school, the Paul-Gerhardt-Gymnasium in Gräfenhainichen, Germany. With permission.)

It looks like it is 12:30 p.m., yet my sister’s friend vouched that it was about 2 p.m. when she took the photo.

Aside from the artwork depicting the various subject areas taught at a high school, there is a diagram showing the time correction, also known as the equation of time. Here it is depicted as a wavy line across the months with the time correction in the vertical. On globes the wavy line is folded into a figure eight and is called the analemma, usually positioned in the Pacific because there’s plenty of space.

In early August there was a plus-25-minute time correction, and in the lower left it explains to add one hour for daylight saving time. Thus, 12:30 plus 0:25 plus 1:00 is indeed 1:55 p.m., which matches the time that Sanny read off her wristwatch. (Due to the longitude of this small town, there also is a 10-minute correction, for it being just a little west in its central European time zone, incorporated in the diagram.)

A sundial always shows local time with 12 noon also called local noon. If Earth was orbiting on a perfect circle and if there were no tilt of the axis, then each day (from one local noon to the next) would be exactly 24:00:00 long. However, the Earth’s tilt on its axis and orbit on an ellipse (though so little elliptical that it could be mistaken for a circle) affect the length of each day.

The axis tilt changes the sun’s apparent motion along the ecliptic from a bona fide, east-west motion to one that has got a slight south-north or vice-versa component. (This is really tough to explain with just the written word. See analemma.org for a comprehensive and good, but equally difficult, explanation.)

Earth on its slightly elliptical orbit is slowed or sped up by the sun’s gravitation. It is fastest in January at 68,000 mph and slowest in July at 67,000 mph.

Both effects require the Earth to rotate a little more or little less to get back to local noon, changing each day, from one local noon to the next, by a few seconds.

That accumulates to the sun “being late” by up to 15 minutes in February and in July, and early by up to 15 minutes in May and in November. These times add to the 30-minute maximum time correction as seen in the diagram.

Sundials used to be ubiquitous until the advent of mechanical clocks a few centuries ago and local noon was used until time zones were introduced around 1880. For railroad travel, especially in the continental United States at that time, standard time zones proved much more convenient than each town using its local noon.

Andy Veh is an associate professor of physics, math and astronomy at Kenai Peninsula College.

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