All five naked-eye planets are on display and the Moon is new.
The five-planet show reaches its crescendo this week, thanks largely to the activities of the solar system’s fastest-moving world, Mercury. The little planet is at the midpoint of its finest showing in 2018. Mercury shines at magnitude –0.4 and sets roughly 1½ hours after the Sun. If you haven’t glimpsed this elusive target before, now is a good time to try. Not far from Mercury is the brightest planet of them all, Venus, which gleams at magnitude –3.9. That said, the evening “star” is still poorly positioned, sitting only about 12 degrees above the west horizon at sunset. The rest of the solar-system action occurs after midnight. Mighty Jupiter glows at magnitude –2.3, rises at around 12:15 a.m. local daylight time, and is past the meridian by the start of morning twilight. Dawn’s other planets are Mars and Saturn, both residing in northern Sagittarius, low in the southeast. The pair are closely matched in brightness, with Saturn at magnitude 0.5 and Mars just a touch fainter at magnitude 0.6. Telescope users can enjoy reasonably good views of Saturn’s rings, but Mars is unlikely to appear as more than a small, fuzzy disc.
Mercury is at greatest elongation today, positioned 18 degrees east of the Sun in the evening sky. This also happens to be when the planet is highest above the Western horizon during twilight and at its best for all of 2018. In a telescope at high magnification, Mercury currently appears as a tiny gibbous disc just 6 arc minutes in diameter—only a little smaller than Mars.
The Moon is new today at 9:12 a.m., EDT.
This evening, a razor-thin crescent Moon sits a little less than 4 degrees to the left of brilliant Venus, low in the west during twilight. You’ll need an unobstructed horizon to view the pair. Venus should be obvious, but you may need binoculars to locate the lunar crescent. The best strategy is to sight Venus first in your binos, get a sharp focus, then move the planet to the right side of the field—the Moon will come into view on the left edge.
Evenings over the March 16 – 18 weekend are free of moonlight, which makes them ideal for deep-sky observing. And if you want to go all out, this is the best weekend of the year to run a Messier marathon.
What’s a Messier marathon? It’s simply a one-night attempt to view as many Messier objects as you can. In theory, it’s possible to see them all in one dusk-to-dawn session during a short period in early spring, when the’s position Sun on the ecliptic is in a Messier-free gap. However, in practice, it’s very, very difficult to log all 110 Messiers in a single night. From Canadian latitudes, it’s simply impossible. So, instead, if you’re feeling up for an all-nighter, the goal is to catch as many Messiers as you can.
The most challenging stretch of the marathon is the large area covering Coma Berenices, western Virgo and eastern Leo. This “Coma-Virgo” region is swarming with faint, formless galaxies, and sorting out which is which can be a daunting task. But if you do well here, it’ll really boost your score. The other difficulty lies in catching stuff in twilight—it’s always a race against time to observe evening objects before they set, while the sky is still darkening, and to claim morning Messiers as they slowly rise in a quickly brightening sky. Careful planning is the key to success. Thankfully, Larry McNish of the RASC Calgary Centre has put together the Messier Marathon Planner to help out. Input your location and other parameters, and Larry’s Planner generates a customized observing list that displays the objects in the order they’re best attempted.
Charging through the Messier catalogue in a single night isn’t everyone’s idea of a good time, but it can be rewarding. The main thing is to have fun and keep in mind that the final score is less important than the game itself.