November Skies 2018

The Solar System

November will bring interesting observing opportunities for some of the planets (stay tuned!), but if you need one word to describe viewing Mercury this month, it’s “Meh.” The planet will be a difficult binocular target as the month begins—determined folks can look for it very low in the southwest, about a half-hour after sunset. Mercury’s angular separation from the Sun increases until the 6th, improving the situation slightly (and for a few days that follow); after that, though, it appears closer and closer to the Sun until it’s lost in glare.

Happily, Venus is a different story—it’s now a pre-dawn object—though just barely so on November 1st. As the month begins, Venus will span 60”—a full arc-minute—across, and would appear as a pencil-thin crescent. That is, if you can see it sharply—it will be only 1° above the eastern horizon, half an hour before sun-up. On a more realistic basis, the planet will display a thin crescent and almost as large a disk (58”) a week later—and by then, it will be a much more reasonable 10° up, 30 minutes before sunrise.

As November progresses, Venus will sit higher and higher before dawn; by month’s end, its disk will have brightened to nearly -5 magnitude (!), with a more usual 40” disk and a thicker-looking crescent phase. If we have good weather this month, Venus should be a real treat.

As for Mars, views of the Martian surface as October ended still showed traces of detail, especially in pronounced features like Syrtis Major. Early November should offer similar opportunities, as the planet’s disk remains about 12” across. By the 20th or so though, the disk shrinks to 10”—a measurement often cited as the cutoff for seeing detail on the red planet. By month’s end, the disk shrinks further, to just over 9”.

After that, Mars will remain an obvious disk in a telescope for months yet, so it will retain some interest for those who have yet to view this planet telescopically. (For a striking contrast, try looking at the color of Mars and comparing it to that of Uranus.) For those more accustomed to great views of the Martian surface, November marks the end of the show for now. Take heart, though; our next chance is in 2020—and we’ll get much sharper views then, as the planet will appear much higher in Denver’s sky than it did this time around.

Two more quick notes: Look for a pairing with the Moon on the 15th—they’re closest, about 1½° apart, around 11 PM. And set a date for a very close conjunction with Neptune next month, on the night of the 6th.

Technically, Jupiter should be visible, a few degrees above the southwestern horizon, in early November, but for all practical purposes, it’s lost in sunlight for most of the month. Jupiter will reappear as a pre-dawn object in late December (look for a close conjunction with Mercury on the morning of December 21st.)

For Saturn lovers, look while you can—in early November, the planet remains high enough for a brief telescopic view right when the sky gets dark enough. By month’s end, though, it will be too low for a sharp image, and it will be lost in solar glare by mid-December.

Just past opposition as November begins, Uranus transits (is highest in the south) just after midnight. It’s close enough to Omicron (ο) Piscium to almost share the same 4° Telrad (or finderscope) field. To ensure the planet appears in your finderscope, center Omicron and then slew your ’scope eastward until the star is on the outer (4°) Telrad circle—that should put Uranus near the northern end of your finderscope’s view.

By the end of November, Uranus transits much earlier, at just after 9 PM. By then, simply centering Omicron Piscium will put the planet in your finderscope, easy-peasy.

Neptune more or less maintains its position in our sky all month, just 2° east of 4th-magnitude Hydor, aka Lambda (λ) Aquarii. Center Hydor in your Telrad, slew your ’scope eastward until the star is on the western edge of the outermost Telrad circle (as above for Uranus), and Neptune should be in or near your finderscope’s crosshairs—this is a good opportunity to find this planet easily.

Neptune is high in the southern sky at 9 PM in early November, and beginning to sink low in the southwest at that hour by month’s end. Remember to use high power to see this planet as a disk—even at 200x, it will appear quite small.

Stars and Deep Sky

This month, we have two objects in Cassiopeia—one that should be easy to see in most amateur telescopes, and one that will be more challenging.

Our first target, M52, at 23h 26m, +61° 41’, is a beautiful and reasonably bright open cluster. (For the uninitiated, an open cluster is a grouping of stars born from a large cloud of gas and dust like the Orion Nebula—or, as we’ll see, our next target. After the stars form, the surrounding nebula gets blown away, revealing the cluster.) With about 200 members, M52 isn’t the biggest cluster, and at magnitude 6.9, it’s not as bright as some others, like M11—or the Pleiades, for that matter. But M52 has its own tricks up its sleeve.

For one thing, M52 is tightly packed—many sources report a central density of three stars per cubic parsec. (In comparison, if we could look at our Sun centered in its own cubic parsec of space, we’d see it’s the only star there.) M52 is also young, as far as clusters go, so it still has a good number of hot—and bright—class-B blue stars among its members. In practice, these qualities mean that M52 is a wonderful target, even in small ’scopes, because its light is concentrated both by its density and by the high output of the stars within it.

A recent observation underlined this quality—M52 remained a good target in an 8-inch ’scope, in spite of the combined effects of an almost-full Moon, moderate light pollution, and atmospheric haze. Under those conditions, my observing partner and I saw gorgeous views at both 80x and 200x. The former showed the whole cluster, in a roughly ½° field, and bordered by a “chain” of stars when we slewed slightly to the southeast. (The stars have different distances from each other and the cluster, so they’re a line-of-sight coincidence—but they’re beautiful, and they make a great landmark for confirming you’re in the right place.)

The 200x view was stunning, even though its smaller field doesn’t show the full cluster at one time—it does certainly show the center. The extra magnification allowed us to see more deeply into the cluster than in the lower-powered view, and we noted a beautiful curving arc of stars, like a “C,” with one star (or a grouping of them) in the center. (My notes from a much earlier observation with a 12-inch Newtonian under city lights, mentioned a noticeably yellow star among the cluster—it’s a former blue star, now swelled up in the process of dying. With the 8-inch under “iffy” skies, that star was visible, but its color wasn’t noticeable.)

Don’t worry if your ’scope has a small aperture—M52 will look fine under a dark country sky in a 4-inch ’scope. Even binoculars or a finderscope should show it, though they won’t resolve the stars.

Star Chart for November 2018 Skies.
Looking due north and about 70° up in Denver at 9:00 PM on November 15th—Cassiopeia’s outline appears like an “M” at this time and date. The Telrad circle is shown centered on M52; note how the distance between the edge of the Telrad’s outer circle and Beta (β) Cassiopeiae is the same as the Telrad’s outer circle itself—about 4°. Stars are plotted to magnitude +6.5, about the limit of the unaided eye in a dark sky; deep-sky objects are shown down to magnitude +10.0. –Object positions, constellation and meridian lines charted in SkySafari, and then enhanced. (Click on image for enlarged version.)

To find M52 around 9 PM mid-month, look high up and due north for Cassiopeia—its famous “W” shape will look more like an “M,” but it should be quickly recognizable. (Early in November, the constellation will appear somewhat eastward of north, and later in the month, it will lie somewhat westward.)

Now look for the two bright stars that make up the M’s left side—they’re Shedar, aka Alpha (α) Cassiopeiae, and Caph, aka Beta (β) Cassiopeiae. Imagine a line from Shedar to Caph, and extend it about 6° beyond Caph to M52. To measure that distance easily, remember that the Telrad’s outermost circle is 4° in diameter, and look at it for a moment to get a feel for its size across the sky. Then slide your Telrad down the Shedar-Caph line until the Telrad’s trailing edge winds up that same Telrad-circle width past Caph, and you should be very close to M52. (The 4° gap you create, added to the 2° from that trailing edge to the Telrad’s center, will give you the 6° separation you need—see chart.)

On a good night, M52 should show up as a smudge in your finderscope, allowing you to center it easily—but if not, you should still be close to having it in your telescope eyepiece, so spiral gently around the area if it’s not initially visible.

Our next object, NGC 281, is often referred to as the Pacman Nebula. Located at 00h 54m, +56° 42’, in Cassiopeia, this underappreciated object is an H II region—a cloud of ionized, glowing gas and dust, like the Lagoon Nebula (M8) in Sagittarius or the famous Orion Nebula (M42). These clouds are often referred to as “stellar nurseries” because the density of the clouds’ material allows “clumps” to form—these clumps eventually collapse in on themselves, compressing their interiors enough to become stars.

In a sense then, these aren’t so much stellar nurseries, as “open-cluster nurseries,” because such clouds give birth to large numbers of stars, grouped in clusters, just as we saw at M52, above. This also helps explain another term for glowing gas clouds like this, “emission nebulae”—the energy from all the hot new stars in and around the cloud excites the gas, causing the nebula to emit light. (This is much the same idea as running electric current through a fluorescent tube to make it glow.)

Unlike the Lagoon or Orion nebulae, though, the Pacman might be a bit more of a challenge to see. In that respect, it reminds me of the North America Nebula (NGC 7000) in northern Cygnus, another vast, glowing cloud of gas. Many sources express frustration with the North America, saying it’s difficult or “impossible” to see it in a telescope, and often suggesting binoculars instead—but stay with me for another moment, and you’ll see what we’re up to!

Like the North America Nebula, the Pacman has low surface brightness, and can be difficult to separate from its background in a telescope eyepiece. However, as with the North America, it’s an interesting object, and it really benefits from a UHC or O III filter—with either, the Pacman pops nicely into view in a dark country sky.

It’s also essential to back off your magnification with this object and use low power, at least until you have it located. Ironically, reports of seeing NGC 281 in 50mm finderscopes or 80mm telescopes are fairly common, but some folks with big aperture give it up. That might seem counterintuitive, but the small instruments’ low magnification helps concentrate the nebula’s light in a small area, so it can be detected by the eye.

I suspect that some users of big-bore ’scopes are mistakenly tempted to boost initial magnification. (With compact light sources, like stars or smaller deep-sky objects, higher magnification can indeed help detection—we just saw this with M52’s stars.) Along with dissipating the Pacman’s light, though, moderate to high magnification might also enlarge this nebula’s image enough for it to extend outside the field of view—just as with the “difficult” North America Nebula, failing to see the edges can make this target difficult to spot.

Keep in mind that the Pacman spans almost half a degree photographically, and only a little less visually (users of standard Plössl eyepieces, for example, are pushing their luck by 80x). In my 12-inch Newtonian, keeping the power down works very well—a 60x view (with a wide-field 25mm eyepiece) gave me a viewing angle of just over 1°, and I saw the nebula clearly with a UHC filter—on a lousy night with bad haze, when my eyepieces were fogging up in the cold. If you don’t have a fancy 25mm, try a 32mm Plössl on the Pacman—it’s an inexpensive solution for folks with Maksutov and Schmidt-Cassegrain ’scopes, even with focal lengths as long as 2,000mm.

In the eyepiece, the Pacman somewhat resembles its video-game counterpart—but the nebula’s “mouth” isn’t the empty space it appears to be—quite the opposite! It’s actually an area of dense material, similar to the dark lane in the Lagoon Nebula (or for that matter, the dark area in Orion’s Flame Nebula, NGC 2024, which we explored in January 2018). It’s filled with activity, including water masers, all hidden within the cloud. To bring a sense of scale to your observation, consider that the Pacman appears dimmer than its famous counterparts mostly because we’re looking at it from 9,000-10,000 light-years away (that’s roughly double our distance to the Lagoon, and six or seven times the distance to the Orion Nebula).

Getting to the Pacman Nebula, NGC 281, shouldn’t be difficult. First look for Achird, aka Eta (η) Cassiopeiae, which is the next reasonably bright star from Shedar as you head towards the middle of Cass’s “M” shape (see chart). Now imagine a line between Shedar and Achird as the base of an equilateral triangle, with the top of that triangle to the southeast, in the direction of Andromeda. Centering your Telrad on that point should put the Pacman in your eyepiece—if you have your position right, you’ll notice both Shedar and Achird appear about halfway between your Telrad’s biggest (4°) and mid-sized (2°) circles.

Happily, this arrangement should put the nebula off-center in your eyepiece, minimizing the chance you’ll fill the whole field with the nebula, and maximizing your ability to detect its edge.

—See you next month.

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