Spring arrives with an equinox full Moon and a parade of planets at dawn.
For planet watchers, the story this week is one at dusk and three at dawn. The dusk world is, of course, Mars. I say “of course” because Mars has been a fixture of the evening sky since last July and will remain so well into July this year. As it makes its way eastward through Aries and crosses into Taurus, Mars shines at magnitude 1.4. Our dawn trio consists of Jupiter, Saturn and Venus. Of these, only Jupiter is ripe for telescopic inspection. Big Jove rises a little before 2:30 a.m., local daylight time and gleams at magnitude –2.2. Next up is Saturn, which clears the southeast horizon before 4:30 a.m., glowing at magnitude 0.6. Last to appear is the reigning morning “star,” magnitude –4.0 Venus, which pops up around 6 a.m., just as the sky begins to brighten with twilight. The planetary parade is a lovely sight, but doesn’t last long in the encroaching dawn.
Sky watchers in eastern Canada have the best seat in the house as the waxing gibbous Moon sits near 1st-magnitude Regulus at dusk. The two objects will be at their closest at around 8:30 p.m., EDT, when they’re separated by roughly 2 degrees. Binoculars are the best instrument for viewing the pairing.
The equinox occurs at 5:58 p.m., EDT, marking the beginning of northern-hemisphere spring. Coincidentally, the Moon is full at 9:43 p.m., EDT, this evening.
If you live under dark skies, take advantage of moonless evenings beginning tonight and for the next two weeks to seek out the zodiacal light. The phenomenon results from sunlight scattered by dust particles residing in the inner solar system. Look for a cone-shaped luminance in the west after darkness falls. Usually, the zodiacal light is about as bright as the winter Milky Way.
Observers located in the eastern half of Canada can enjoy a double-shadow transit on Jupiter this morning. Things get started at 4:06 a.m., EDT, when the shadow of Europa lands on the Jovian disc, joining the shadow cast by Ganymede. The double-transit wraps up two hours later when Ganymede’s shadow slips off Jupiter’s western limb. You’ll need steady seeing conditions and high magnification in your telescope to witness this event.
Nights over the March 22 – 24 weekend are lit by a bright, waning gibbous Moon. However, early evenings are moonfree, offering observers a fine opportunity to enjoy some winter sights on the first weekend of spring. Perhaps most appealing for naked-eye observers is an impressive collection of stellar luminaries. Face south-southwest at nightfall, and no fewer than seven stars of first magnitude or brighter can be taken in with a single view. Most are included in the Winter Hexagon, as shown in the chart above.
Let’s begin at the bottom of the Hexagon with Sirius. At magnitude –1.4, Sirius dominates Canis Major and is the brightest star in the night sky. It’s also one of the nearest. At a distance of only 8.7 light-years, Sirius is the closest star we can see from Canada without optical aid. Proceeding clockwise, we reach Procyon (magnitude 0.4) in Canis Minor, then Pollux (magnitude 1.2). Pollux and nearby Castor are the so-called Gemini Twins, though the two are not exactly twins when it comes to brightness (Castor is two-tenths of a magnitude too dim to qualify for membership in the first-magnitude club).
Next in the Hexagon, high overhead, is Auriga’s leading light, Capella. At magnitude 0.1 Capella is second only to Sirius among brilliant winter stars. Turning south, we come to Aldebaran (magnitude 0.9) in Taurus. Can you detect its golden hue? Aldebaran is not as red as Betelgeuse, in Orion, but its colour should be quite apparent. The last stop on our tour is Rigel, also in Orion. There’s a nice symmetry to concluding with Rigel. We began with the closest star in the Hexagon, Sirius, and we end with the most distant. Rigel is roughly 100 times farther away than Sirius and yet, at magnitude 0.2, is only a little fainter. How can that be? As it turns out, a star’s brightness depends both on its distance and its intrinsic luminosity. Rigel is a blue supergiant shining with more than 100,000 times the intensity of our Sun. Indeed, if all the points on the Winter Hexagon were at the same distance from Earth, Rigel would best Sirius as the sky’s brightest star by a huge margin.
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