Highlights of the Season: October-December 2022

On October 22, Venus is at superior conjunction. The term refers to the type of conjunction that occurs when Earth, Venus, and the Sun form a line. Because Venus orbits inside the orbit of Earth, it can pass between Earth and the Sun. This is an inferior conjunction, when Earth and Venus are closest together and only about 61 million kilometers (29 million miles) apart. This is when Venus looks largest, with an apparent diameter of roughly one minute of arc (64 seconds of arc or about 1/60 of a degree). On the other hand, at superior conjunction, Venus lines up on the far side of its orbit so that the Sun is between Earth and Venus, and Venus' distance from Earth is increased by the diameter of its entire orbit, putting it 261 million kilometers (162 million miles) away. At that distance it looks 1/6 the apparent diameter we see at inferior conjunction.

Image credit: Statis Kalyvas

The second partial solar eclipse of 2022 occurs on October 25, as the new Moon moves between Earth and the Sun—but not quite enough to completely block the Sun from view, so part of the Sun's disk is visible and neither totality nor annularity occur. The eclipse is visible in varying amounts from most of Europe, along with northern Africa, the Middle East, and western parts of Asia. Maximum eclipse (magnitude=0.86) will be observed from the West Siberian Plain in Russia near Nizhnevartovsk, where the silhouette of the Moon will encroach 86% of the way across the Sun's diameter. An interactive observability map can be found at www.timeanddate.com/eclipse/solar/2022-october-25.

That misnomer is often mistakenly applied to the lunar far side, which always faces away from Earth. However, the Moon's "dark side" is simply whichever side the Sun isn't shining on. For about an hour on November 7-8, none of the Moon will be in direct sunlight as our satellite takes a plunge through Earth's shadow, causing a total lunar eclipse, darkening in varying shades of reddish-orange to grayish-brown. Centered over the Pacific Ocean, this is visible from North America, favoring observers west of a line drawn from Lake Winnipeg to mid-Baja California, who will experience the event from start to finish. As seen from San Francisco, the fun happens after midnight, with partiality beginning at 1:09 am on the 8th as the inner portion of Earth's shadow (the umbra) starts creeping visibly across the Moon's face. Totality lasts from 2:16-3:41 am, and the eclipse ends at 4:49 am as the umbra departs the Moon's disk.

Additional details (a simulation, exact times of various stages, and interactive observability maps) can be found at www.timeanddate.com/eclipse/lunar/2022-november-8, and here's a video about observing lunar eclipses and why they occur: www.calacademy.org/explore-science/how-to-observe-a-lunar-eclipse.

On November 9, the distant planet Uranus reaches opposition. As with oppositions of other celestial objects, this is when it's located opposite the Sun in the sky and rises at sunset. Even though this is when it and Earth are closest, the distance between them is an enormous 1.7 billion miles.Uranus' angular diameter is 3.8 arcseconds (about 1/500 the diameter of the full Moon) and it's a barely-visible magnitude 5.7, which is as faint as most people with sharp eyesight can see under perfect, moonless observing conditions.

However, the 9th is the day after a full Moon whose bright light will obscure the view. Uranus moves very slowly, so it'll be there for a while, allowing observers to wait for that pesky Moon to move to another part of the sky. Starting on the 11th or 12th, during the first couple of hours after nightfall and before moonrise, observers with binoculars or a telescope should look for a tiny, steadily shining greenish disk about 14° southwest of the Pleiades star cluster in Taurus the Bull.

During the 1877 opposition of Mars, Italian astronomer Giovanni Schiaparelli noted what he perceived as faint lines criss-crossing the face of Mars, calling them "canali," an Italian term by which he simply meant "lines." However, the word was mistranslated into "canals" in English, leading a number of people—American Percival Lowell among them—to think that Schiaparelli was in fact referring to a network of waterways built by an intelligent civilization inhabiting the Red Planet. Lowell would become the foremost champion of the idea, but today we know that the canals never existed and were the result of human imagination running a bit wild with the illusion of lines in the tiny, blurry images produced by the telescopes of the day (Schiaparelli used an 8.7 inch refractor).

So…no, even with modern instruments, you won't see any canals because they're simply not there. If, however, the opposition occurs during a cooperative season on Mars, you might see an ice cap or some dark patches on the planet's surface. On December 7, Mars' opposition distance is 38.6 million miles (62 million kilometers)—a bit farther than its distance of 35 million miles (56 million kilometers) during the opposition of 1877, when Schiaparelli first thought he saw the imaginary "canali."

On December 7, not only is Mars at opposition, but by definition, so is the full Moon, and both will line up so that observers in certain locations will see the Moon move in front of the Red Planet and hide it from view for about an hour. The viewing area covers Canada, most of the US (except the southeastern states), Greenland, western Europe, and Scandinavia. For observers in San Francisco, the occultation begins at 6:34 pm PST, when the Moon and Mars are both 21° above the eastern horizon against the stars of Taurus the Bull. By the time occultation ends at 7:37 pm, when the Moon uncovers Mars, both will have risen higher in the sky to an elevation of 33.8°. More info is at https://in-the-sky.org/news.php?id=20221208_16_100.

• December 21 is the winter solstice, when the north pole of Earth's axis leans farthest away from the Sun. This makes the Sun seem to follow its lowest and shortest arc across the sky, causing shorter daylight periods and longer nights in the northern hemisphere. At the north pole, the Sun is not visible at all, so there is no direct sunlight, and night lasts 24 hours.
• In some traditions, the solstice is referred to as Midwinter's Day and marks the middle of the season. In this tradition, seasons begin on cross-quarter days (the halfway points between the equinoxes and the solstices, or February 2, May 1, August 1, and October 31).
• While many of us are familiar with the astronomically based definition of the seasons, there's another definition that has come into use—the meteorological seasons, which are based on annual temperature patterns and last for three months each, starting on the first day of the month in which the equinox or solstice occurs (December-February, March-May, June-August, and September-November).
• In the southern hemisphere, the Earth's south pole is tilted toward the Sun, making December 21 the summer solstice, marking the start of the summer season south of the equator.