by Zachary Singer
Along with the planets this month, we’ve got two targets in the constellation Canes Venatici—one is a sun-like star, and the other a bright spiral galaxy. Let’s get going…
The Solar System
Mercury starts May as a morning object, technically speaking—it’s very low on the horizon before dawn, and moving closer to the Sun daily. The planet lines up with the Sun, at its superior conjunction, on the 21st, and will be lost in sunlight well beforehand. Mercury will reappear towards the end of the month as an evening object.
Venus remains a bright pre-dawn target, shining at magnitude -3.9 all month. The planet’s position, though, is narrowing its apparent angle from the Sun as we see it from Earth—in early May, Venus is already less than 6° above the eastern horizon, 30 minutes before sunrise. By month’s end, that angle decreases to just over 4°. As Venus gets closer to lining up with the Sun at its superior conjunction this August, its disk will become more fully illuminated—or more simply, closer to a “full” phase.
Mars is now so far from us that its increasing distance no longer makes an appreciable difference. From our point of view, Mars’ disk continues to shrink, but it will essentially remain at roughly 4” all month, as its loss in angular size is merely a fraction of an arcsecond. Look for Mars low in the west in evening twilight—in the “horns” of Taurus in early May, and by the “knees” of the Gemini Twins late in the month.
Jupiter is now an “evening” object, under a very liberal definition, since it currently rises an hour before midnight. On a more practical basis, that means acceptable, if a touch blurry, observations just after 1 AM, with improved views an hour or so later, when the planet will be higher in the sky and thus sharper-looking.
By the end of May, these timings will occur two hours earlier, putting Jupiter in a good position for observing at a fairly reasonable hour. Jupiter is at opposition next month, when it lies directly opposite the Sun as seen from Earth. At that point, the planet will transit, or appear highest in our local sky, around 1 AM. The situation will continue to improve after that, too!
Finding Jupiter is easy, as it appears just “above” Scorpio and Sagittarius—it’s the brightest object in this part of the sky, except for the Moon. The only other body that outshines it is Venus, which won’t rise for hours after Jupiter does—by then, Jupiter commands the southern sky.
If you’re new to observing Jupiter, any telescope will show you the planet and its four “Galilean” moons, which as their names imply, were discovered by Galileo. These moons appear as little white dots more or less in the plane of Jupiter’s equator; careful observation will show you their motion, even over a period of hours. These moons pass each other in their orbits, cast shadows on Jupiter’s surface, and can be seen to “rise” and “set” behind the planet at predictable intervals.
You’ll need calm skies and a large aperture to see the moons’ shadows on Jupiter, but the other events are easily seen— monthly astronomy magazines and popular software for smartphones or computers can tell you when to look. The bands in Jupiter’s atmosphere are fascinating too, and a good ’scope can show you mesmerizing detail, including Jupiter’s famous Red Spot, an Earth-sized storm. Recent observations in steady skies during the wee hours have been stunning.
Saturn is becoming an increasingly accessible target, too, rising just after 1 AM in early May. Determined observers can expect an imperfect but satisfying view about two hours later—as with Jupiter, waiting for Saturn to climb higher into our sky will improve sharpness. By the end of the month, Saturn will be nearly as high by 2 AM as it will get, so sharp views won’t be too difficult, and the beforementioned “imperfect” views will be available earlier, too. Though not as brilliant as Jupiter, Saturn will look like a bright “star” to the northeast of the Sagittarius “teapot” all month.
Uranus will be lost in solar glare this month, and will emerge as a pre-dawn object in June.
Neptune sits low in the pre-dawn sky as May begins. By month’s end, though, the planet is more than 20° up in a dark sky around 4 AM, 90 minutes before dawn. If that’s too crazy an hour for you, take heart—it will be up much earlier in the coming months.
Stars and Deep Sky
Our targets this month lie in the unassuming-looking constellation Canes Venatici, which lies less than 15° “below,” or south of, the handle of the Big Dipper. Just two reasonably bright stars form its simple outline—Cor Caroli and Chara (one of our targets)—so our first stop won’t be hard to find.
It’s worth mentioning that although Canes Venatici has a small outline, the area is rich in targets, including some fascinating galaxies, like M51, the Whirlpool; M94 and others. Cor Caroli is a beautiful, blue-and-white binary star, and M3 is a spectacular globular cluster. (M3, Cor Caroli and M51 are covered briefly on pages 6-7 in the June 2015 Observer; M94 on pages 6-7 of the May 2018 Observer. Both issues are in PDF format.)
If you peer at a star chart, you’ll see Chara on the opposite end of a simple line from Cor Caroli—it’s also known as Beta (β) Canum Venaticorum—or Beta (β) CVn for short, and in some guides (or “go-to” controllers), it’s 8 CVn. For those of you using celestial coordinates, you’ll find Chara at 12h 35m, +41° 15’. Apart from being a great guide for star-hopping, Chara has an interesting characteristic: it is quite sun-like.
According to one of my favorite sources, Prof. James Kaler of the University of Illinois, Chara is a class G0 star, radiating light at about 5880 K. That’s just a trifle hotter than our Sun; Chara is also just a fraction of a magnitude brighter than our Sun, as seen at the same distance—in short, Chara (aka β CVn) makes a great stand-in for our own home star.
So, here’s the thing—when you’re out under a dark sky, looking up at Chara, notice how “mediocre” it is in brightness, at about magnitude +4.2 as seen from Earth. In a clear dark sky, it won’t be hard to spot, but you won’t say that it’s striking, either. Our Sun would look much the same way, if it were where Chara is. While Chara is visible out in the country, it’s easily washed out by city lights, and requires binoculars or a finderscope in southern Denver. (It’s barely visible south of Chatfield Reservoir or in exurbs like Castle Rock).
For additional perspective, look back at nearby Cor Caroli—it’s “beaming” in comparison, at magnitude +2.9—and it’s about four times farther away from us than Chara is. If Cor Caroli were at Chara’s distance, it would appear three magnitudes brighter, blazing at magnitude -0.1, easily bright enough to overpower heavy light pollution in Denver or even Los Angeles. Conversely, if Chara were at Cor Coroli’s distance, it would dim to a mere magnitude +7.2—for most of us, that’s too dim for naked-eye vision, even in the most pristine dark sky.
Chara’s 27 light-year distance is both a great span and very near, both at once. On the one hand, a single light-year is more than 60,000 times the Earth’s distance from the Sun—so when we say Chara is far away, that’s certainly right!
On the other hand, distances within our Milky Galaxy use a vastly grander scale, and 27 light-years doesn’t amount to much. While the nearest star to the Sun is only 4½ light-years away, the galaxy itself is roughly 100,000 light-years across. On that scale, Chara is sitting right next to us. It certainly puts our Sun’s brightness into perspective, when we realize that Chara, its stand-in, is already of such unimpressive brightness at such a meager distance.
Unlike most of our targets, we don’t have to worry about the size of our telescope, or which eyepiece to use—Chara will be visible in any of them. Rather, just experiment with your gear to see which gives you the most aesthetic view, remembering all the while that our Sun appears similarly at this star’s distance.
Directions
Finding Chara is simple, once you’re familiar with Cor Coroli and Alkaid (the latter is the bright star at the end of the Big Dipper’s handle). If you can find those two stars easily, skip the next paragraph, and go to “To get to Chara,” below.
For everybody else, look straight up around 10 PM in May, and you’ll see the Big Dipper high overhead. Now look for the star where the Dipper’s “bowl” joins with its “handle.” Imagine a line from there to Alkaid, at the handle’s end, and make a loose right-angle from there southward, towards Leo’s tail. You’ll quickly notice Cor Caroli, at about the same distance “below” Alkaid as Alkaid is from the Dipper’s bowl. (See main chart, above.)
To get to Chara, just start at Cor Caroli under a clear dark sky and look 5° northwest (about half the width across your knuckles when your arm’s outstretched), and there you are—Chara is the only star of this brightness in the vicinity. An easy way to find the right direction is to make a 90° turn from the Alkaid-Cor Caroli line, heading back “underneath” the Dipper. You can also imagine moving parallel to the line from Dipper’s handle to its cup.
In a light-polluted sky, you won’t see Chara naked-eye, but if you want to view it in your telescope, first center your Telrad on Cor Caroli. Then slide it in the direction given above, until the Telrad’s center is roughly a Telrad-width from where you started—that should put Chara into your finderscope, and you can put it in the crosshairs yourself from there.
Our second target is the bright galaxy, M63, aka the Sunflower Galaxy, at 13h 17m, +41° 56’. It’s one of only about 30 galaxies visible from Denver’s latitude that are magnitude +9 or brighter.
M63 is a “flocculent” galaxy, a subtype of spiral galaxies; unlike “grand design” spirals, like the Whirlpool (M51), flocculents have numerous “mini-arms,” instead of a few larger ones. To our eyes, these arms seem to “clump” together, forming an indistinct, mottled, or somewhat “fluffy” mass. (Some sources also describe such galactic arms as “tightly wound.”)
This type of galaxy is also represented by NGC 2841 in Ursa Major, which we toured in the April 2016 Observer (see the very last paragraph on page 7 of the PDF, continuing on page 8). Both galaxies are of similar intrinsic luminosity, with an absolute magnitude of about -21 or brighter; the arms of both are also areas of recent star formation, with notable numbers of hot blue stars.
Like NGC 2841, M63 has a bright innermost region, surrounded by its many arms. In turn, a much wider area surrounds that, giving the Sunflower Galaxy its appearance and informal name. It’s somewhat closer than NGC 2841, and thus appears brighter to us—at magnitude +8.6, the Sunflower is an easy object in a moderate (6-inch) ’scope, and observers under a clear dark sky shouldn’t have trouble seeing this in a 4-inch.
I recently observed the Sunflower under less-optimal conditions—one session was with an 8-inch Schmidt-Cassegrain, in the exurbs. Magnitude 4.2 and 4.3 stars (like those in the constellation Coma Berenices, just south of M63) were near the limits of naked-eye vision, due to haze and light pollution. Under these conditions, telescopic views of M63 using direct vision nonetheless showed a pronounced glow in its center, and its outer glow was easy with an averted glance. Moderate power, about 80x with a wide-field 24.5mm eyepiece, was good for detection, but 160x showed the galaxy much better. It was a very satisfying view, in spite of the limited sky transparency.
For kicks, I also had a go at M63 from southern Denver, where it emerged from the murk of a really rotten, hazy and light-polluted sky in my 12-inch Newtonian. (A waning gibbous moon was coming up too, and Chertan, in the haunches of Leo, was hardly visible in spite of its +3.3 magnitude.) Still, the galaxy was detectable. As experienced observers might guess, it was best at higher powers, where the extra contrast from a darkened sky-background helped pop out the target. The galaxy’s oval appearance was distinct, especially with averted vision—and as expected, brightest towards the center.
While conditions for the latter observation were a bit extreme, both of those noted above demonstrate an important idea—that as for a few other galaxies, like M31 or M82, optimum observing conditions are desired, but not required for M63 (as an aside, M31 can even be seen in binoculars, under Denver’s light pollution). With our ongoing crummy weather here along the Front Range, that could make a real difference for you—at least in a moderate ’scope, M63 can still remain a reasonable target when a little moonlight or haze interferes.
This month, our early “Dark Sky” window was largely washed out, but don’t give up—except for the worst week around the full moon mid-month, most observers should still have luck. By the 21st, another “window” will open after twilight, extending to almost midnight that night—that window of opportunity gets longer each night, and by late in the month, it more or less runs all night. This “window” for observation extends well into June (watch for a similar “reopening” of the observing window after that month’s full moon, too).
Directions
As with finding Chara, above, the key to getting to M63 is the imaginary line between Alkaid and Cor Coroli. (If you’re not familiar with this part of the sky and you skipped looking for Chara, have a look at those directions now.) Once you’re looking along the Cor Caroli-Alkaid line, you’ll quickly notice a small grouping of stars on the chart, about a third of the way up from Cor Caroli, and slightly off the line to Alkaid. The brightest of these is 20 CVn, at magnitude +4.7 (see chart). Since the dimmest of the group is mag. +5.8, some or all should be visible in a dark country sky—even if they’re not directly resolvable naked-eye, you should still get an impression of a “clump” there. Put your Telrad on the group, and then center it inside your finderscope.
In a mediocre sky, these stars could be washed out for the naked-eye—if so, center your Telrad on Cor Caroli, then move it about a third of the way to Alkaid, 4° or 5°, or across the width of two knuckles, held at arm’s length. Some or all of the “clump” should be in your finderscope, or near it. (If Cor Caroli isn’t visible even after spiraling around a bit, wait for a decent night!)
Once the finderscope is in the right place, its field should clearly show at least four bright stars. Three of these conspicuously form a short line, and the fourth star, west of the others, completes a right triangle, using the endpoints of the just-mentioned line as the other two vertices. Center the corner star that sits at that right angle, and we’re almost there.
Now, regardless of its orientation in your finderscope, imagine the triangle’s right angle as its “top,” and the side opposite that angle as forming the triangle’s base, or “bottom.” (If it helps keep you oriented, this bottom lies in the southernmost part of the triangle and actually runs directly east-west between its corners.)
The last step is to imagine a “vertical” line, relative to the “horizontal” bottom, extending straight upward from our right-angle star, 19 CVn—make this new imaginary line the same length as the line of three stars that we started with, and when you have that length in mind, put your crosshairs on that line’s endpoint. M63 should now be in your low-power eyepiece’s field. (See close-up chart.)
As a further guide, notice that 19 CVn is also the vertex between the original triangle’s “three-star” line and the new “vertical” one—the angle between these two lines is about 120°, the same as cutting a pie into thirds, or between the vertical line of an old ’60s peace sign and its diagonals, measured the “thicker” way.)
For users of equatorial mounts: if yours is carefully polar-aligned, then a short, 1° 10’ slew due north from 19 CVn will put the galaxy in your eyepiece, without having to worry about “which side of the triangle is the bottom,” and all that. If you have accurate setting circles, use them—if not, slew a bit less than a degree, so you don’t overshoot, and go the rest of the way while watching through the eyepiece.
At our stated time of 10 PM in mid-May, M63 (and all of Canes Venatici) is painfully close to the zenith for aiming with a straight-through finderscope or a Telrad. (If you’re a Dobsonian user, the scope itself will be a bear to aim when pointing that high.) Give your neck and back a break, and wait an hour or two for M63 to move westward, past its highest point. At this time of year, observing the target earlier, instead of later, isn’t an option, because twilight will interfere.
—Normally, I’d sign off here, saying “See you next month,” but we’re going to use this column’s June 2019 edition to explore some possibilities for its future. Put your thinking caps on, and I’ll see you then.
