TAWBAS star party

This Week’s Sky: March 19 – 26

The Moon visits the Hyades, while Mercury and Venus put on a show in the early evening.

Jean Guimond captured this view showing (from left to right) the Moon, Venus and Mercury from Quebec City on the evening of March 18, 2018. This week, Mercury sinks lower and passes Venus.

All Week

The view facing west-southwest, midweek, 45-minutes after sunset.

As the song says, what goes up, must come down. And so it is with the two innermost planets gracing the dusk sky. On its way up is Venus, which gains a bit more altitude each day. The magnitude –3.9 evening “star” now sets 1½ hours after the Sun. On its way down is nearby Mercury, which is wrapping up its most favourable apparition of the year. Not only is the swift little planet setting earlier each night, it’s also losing brightness. By mid-week it has faded to magnitude 1.1—almost a full magnitude fainter than last week. As it descends, Mercury passes brilliant Venus on the evening of the 21st. Meanwhile, the predawn is populated with a second group of planets: Jupiter, Mars and Saturn. For telescope users, Jupiter is the most rewarding. Gleaming at magnitude –2.3, Big Jup climbs to the meridian just after 4:30 a.m., local daylight time. Trailing behind is Mars, which rises at 3:00 a.m. The 0.5-magnitude red planet is still quite small (8 arc seconds diameter), but by the end of April finally might be worth inspecting in your scope. Last to rise is Saturn, which clears the southeast horizon roughly ½ hour after Mars. The ringed planet shines at magnitude 0.5 and climbs to an altitude of nearly 20 degrees as morning twilight becomes noticeably brighter.

March 20

At 12:15 p.m., EDT, the centre of the Sun crosses the celestial equator, signalling the end of winter and the beginning of spring in the northern hemisphere—a moment known as the spring equinox.

March 22

The Moon and the Hyades cluster as seen in 7×50 binoculars.

This evening the crescent Moon sits near first-magnitude Aldebaran and the stars of the Hyades cluster, in Taurus. For skywatchers across much of Canada, this will be a lovely binocular sight. The best view will be early in the evening—before the Moon exits the cluster. However, those in the western half of the country can enjoy a bonus daylight event when the dark edge of the lunar disc eclipses Aldebaran. The occultation lasts from 2:51 to 3:27 p.m., PDT, as seen from Vancouver, British Columbia. A small telescope, carefully focused on the Moon’s limb, will show the star quite readily even in full daylight. Indeed, the sight of golden, orange Aldebaran against a blue sky is quite lovely. For more on this encounter, turn to page 31 of the March/April issue of SkyNews.

March 24

The Moon reaches first-quarter phase today at 11:35 a.m., EDT, and rises shortly after noon.

March 26

The Moon and M44 as seen in 10×50 binoculars.

This evening the waxing gibbous Moon shares a binocular field with the Beehive Cluster, M44, in Cancer. The two objects are separated by just 1½ degrees at their closest, which occurs at 8:13 p.m., EDT. The sight will be most impressive for observers in eastern Canada—by the time twilight fades on the West Coast, the Moon’s eastward motion will have carried it nearly 1 degree farther from the cluster.

Weekend Stargazer

Mare Vaporum region

Base image courtesy LRO/NASA

Spring evenings are the best time of year for viewing the first-quarter Moon as it cruises along the northernmost reaches of the ecliptic. That makes the March 23 – 25 weekend a particularly fine one for exploring one of the Moon’s most unusual regions. Aim your scope at the stretch of lunar terrain lying in between Mare Vaporum, Mare Serenitatis and Mare Tranquillitatis. (The area is best viewed on Friday and Saturday evenings when the terminator is nearby.) There you’ll find a set of features unlike any other on the Moon. Instead of the usual craters, mountains, or maria, this region is dominated by impressive gouges. And the few craters found here are in pretty rough shape. Julius Caesar, for example, is so distorted it doesn’t look like a crater at all. Nearby Boscovich is battered almost to the point of oblivion. Also, both craters have been partly filled in, giving them a shallow appearance. But what’s going on here? What could possibly account for all this tortured structure?

The answer is Imbrium. Julius Caesar and Boscovich provide graphic evidence of the powerful tsunami of Imbrium ejecta that virtually levelled everything in its path, roughly 3.85 billion years ago when the giant basin was excavated by a powerful impact. And yet, if you direct your gaze slightly north to Manilius you’ll see a very ordinary, 38-kilometre-wide crater that seems to have escaped the scouring from near-surface debris altogether. How? Simple. Manilius didn’t form until long after the dust had settled from the Imbrium impact, proving once again that even on the Moon, timing is everything!

At SkyNews we love to read about your experiences and see your photos. You can share them with us by e-mailing skynews@skynews.ca.

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