October 2022 Giant planets rule the night

As twilight fades to darkness this month, Saturn stands out from its perch high in the northern sky. The ringed planet shines at magnitude 0.5 against the relatively faint backdrop of Capricornus the Sea Goat. The 4th-magnitude star Iota (ι) Capricorni lies less than 1° southwest of the solar system’s second-largest world.

Saturn’s high altitude makes it the top choice for early evening telescope viewing. Even the smallest scope shows the planet’s 18"-diameter disk surrounded by a spectacular ring system that spans 40" and tilts 15° to our line of sight. During moments of good seeing, the Cassini Division appears as a dark gap between the outer A ring and the brighter B ring. Small instruments also reveal 8th-magnitude Titan, Saturn’s largest moon, along with a trio of 10th-magnitude moons.

Jupiter hangs low in the east during twilight in early October. Look for the giant planet’s position to improve dramatically, however, as both the evening and the month wear on. Jupiter gleams at magnitude –2.9 among the background stars of southern Pisces the Fish. That is some 400 times brighter than the constellation’s luminary, magnitude 3.6 Eta (η) Piscium.

Once Jupiter climbs high in the north later in the evening, spend some time viewing it through your telescope. The solar system’s largest world lives up to its reputation in October. The planet spans

50" to start the month and

48" as the calendar turns to November. Small scopes reveal a wealth of detail in Jupiter’s massive atmosphere. Look for a series of alternating dark belts and brighter zones that run parallel to one another. The Great Red Spot should be obvious if it is on the hemisphere facing Earth. And be sure to check out the planet’s four bright Galilean satellites.

The next bright planet doesn’t put on a good show until after midnight. Once the familiar shape of Orion the Hunter fully clears the eastern horizon, you’ll easily spot Mars to the constellation’s lower left. The Red Planet resides in eastern Taurus the Bull, sharing this part of the sky with two other ruddy objects: the 1stmagnitude stars Aldebaran in Taurus and Betelgeuse in Orion. Mars dominates its neighbors, however, brightening to magnitude –1.2 by October’s close.

Mars suffers from a low altitude this month as it travels along the northernmost part of the ecliptic. It reaches a peak altitude of just 30° to 40° as morning twilight commences. Still, the view through a telescope proves worthwhile because the planet’s diameter grows from 12" to 15" during October. This is big enough that most scopes will show surface details under good seeing conditions.

Mercury lies in the morning sky this month, reaching greatest western elongation October 8. Unfortunately, the planet then stands only 18° from the Sun. This small separation combines with the shallow angle between the eastern horizon and the ecliptic to make spotting the inner world nearly impossible from midsouthern latitudes.

Venus passes on the far side of the Sun from our vantage point October 22 and remains out of sight all month.

The starry sky

As the winter Milky Way dips low in the west on October evenings, turn your attention away from our galaxy’s plane. One of my favorite sights at this time of year is the constellation Grus the Crane, which lies nearly overhead in the evening sky.

I first became familiar with this bird in March 1970 when I was keenly following the progress of Comet Bennett as it headed northwest through the constellation. At one point, the comet passed close to the striking naked-eye pair Delta1 (δ1) and Delta2 (δ2) Gruis.

The Crane’s shape is relatively easy to identify. First find the lengthy line of stars that starts with Beta (β) Gru and stretches to the northwest, ending with Gamma (γ) Gru. Beta lies in the main body of the bird, with the Delta1 and Delta2 pair marking the beginning of the Crane’s long neck. The neck continues with another pair, Mu1 (μ1) and Mu2 (μ2), followed by Lambda (λ). Gamma pinpoints the bird’s head and lies near the constellation’s border with Piscis Austrinus the Southern Fish.

In the opposite direction from Beta, the triangle of stars Epsilon (ε), Eta, and Zeta (ζ) marks Grus’ tail. The bird’s wings run perpendicular to this extended line through Beta.

The western wing ends at

Alpha (α) and the eastern wing terminates with the Theta (θ) and Iota pair.

Grus first appeared in its current form in Johann Bayer’s classic 1603 atlas, Uranometria, though he didn’t invent it. Long ago, celestial cartographers deemed the stars of Grus as an extension of Piscis Austrinus. Ptolemy considered the star we know as Gamma Gru as marking the tip of the Southern

Fish’s tail, but Bayer’s chart shows the bird and fish clearly separated. Not long after Bayer’s atlas appeared, a few astronomers tried to turn the Crane into a flamingo and called the constellation Phoenicopterus. (In zoology, the flamingo belongs to the Phoenicopteridae family.) However, no one ever uses this name today.

Intriguingly, Comet Bennett wasn’t the first well-known comet to pass through Grus. Ninety years earlier, the Great Southern Comet of 1880 visited the Crane. Observers reported that this dirty snowball from the outer solar system sported a spectacular tail.