The first-quarter Moon covers Aldebaran and Mercury meets Mars.
Mercury is climbing out of the horizon muck on its way to a favourable evening apparition that continues into next month. The fast-moving planet is low in the west in twilight and shines at magnitude –1. The evening sky is dominated by the planets Venus and Jupiter. Venus is a magnitude –4.1 beacon that doesn’t set until nearly midnight! Jupiter is already past the meridian as darkness falls. The –2.2-magnitude giant planet is well placed for telescopic viewing. Last up is the ringed planet Saturn. It shines at magnitude 0.2 and clears the southeast horizon around 10:30 p.m., local daylight time. The best time to view it in a telescope, however, is around 3:30 a.m., when it’s highest in the sky.
If you live in a part of the country west of Sudbury, Ontario, and east of the British Columbia/Alberta border, you have a chance at seeing a daytime occultation when the unlit limb of the Moon passes in front of Aldebaran, the brightest star in Taurus. This will be tricky to view since it happens in daylight and the Moon is not very high in the sky. A computerized “go-to” telescope makes the task easier. The precise time of the cover up depends on where you live. The lunar disc occults Aldebaran at 9:26 a.m., MDT, from Calgary, Alberta; 9:25 a.m., CST, from Regina, Saskatchewan; 10:26 a.m., CDT, from Winnipeg, Manitoba; and 11:29 a.m., EDT, from Thunder Bay, Ontario.
Later, in the evening, the Moon, Venus and Aldebaran will make for an attractive triangle in the western twilight sky. From Toronto, the lunar crescent will lie a little more than seven degrees from the brilliant planet.
In the predawn sky, look for Saturn forming a neat, symmetrical triangle with the stars Beta (β) and Nu (ν) Scorpii. The ringed planet will be close to Beta for several nights.
This evening Mercury will be near Mars, low in the west during evening twilight. To see this pairing, you’ll need an unobstructed horizon and binoculars. Mars shines meekly at magnitude 1.4 while Mercury is a bright magnitude –1.1.
Tonight the Lyrid meteor shower peaks under moonless skies. The display offers roughly 20 meteors per hour under ideal, dark-sky conditions, radiating from a position west of the constellation Lyra.
The Moon reaches first-quarter phase this evening at 7:55 p.m., EDT. Tonight and tomorrow night it will be positioned a few degrees from Jupiter.
The first-quarter Moon is well placed in the evening sky over the April 24 – 26 weekend. This is a wonderful phase that rewards leisurely telescopic sweeps up and down the terminator where features are most boldly presented. But if you can tear your eye away, direct your attention toward the Moon’s northeast limb, remembering the lunar east and west are opposite sky directions. There you will find a 160-kilometre-wide patch of dark grey known as Mare Humboldtianum.
This mare holds the distinction of being one of only two maria named after people (the other being Mare Smythii). The mare was given its name by Alexander von Humboldt’s friend and Moon mapper, Johann Mädler, illustrating that it helps to have friends in high places. The Humboldt basin (which contains the mare) is one of the best-preserved lunar basins, but is difficult to view since it requires a favourable libration, which this weekend offers. And while you’re in the area, look in on the 125-km-diameter dark-floored crater Endymion. It’s an easier target and can even help you locate Humboldtianum when libration conditions aren’t so favourable.
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