Last week, coffee companion and astronomy commentator Bruce McCurdy
introduced us to this week's promenade of the Moon and the five naked-eye
planets visible in the evening sky.
Thanks to Bruce, I was quite taken with Sunday night's view of Jupiter,
Saturn, Mars and Venus, and especially of the thin crescent moon as it
slipped past Venus low in the west. (Mercury, at the time I was looking,
had already set.) The shadow-side of the moon was dimly but distinctly
visible, illuminated by Earthshine – sunlight reflected onto the
Moon by the Earth. This phenomenon, sometimes known as "the old Moon
in the New Moon's arms," is always awesome to behold.
But there's more awesome stuff to behold over the next few weeks, as
Bruce explains in a further note:
ONE WOULD EXPECT the music of the spheres to be classical music, precise
and majestic. But while the rhythms of the nearby spheres, our planetary
neighbours, are individually tight and predictable (with an occasional
retrograde flourish), as an ensemble they resemble free-form jazz.
Each seems to do its own thing without much regard for the others,
one playing four beats to the bar, another five, another seven-and-a-quarter,
or something. Suddenly they come together for a few bars and the music
starts to make sense before they go their separate ways again. The planetary
polyrhythms are presently at such a point.
Throughout the past winter, mighty Jupiter ruled the celestial dance
floor, gleaming brilliantly high in the southern sky in the constellation
of Gemini. It was accompanied by the ringed wonder, Saturn, in the neighbouring
constellation of Taurus. The two have been passing acquaintances the
past three winters as Jupiter in its smaller orbit has appeared to whiz
by stately Saturn.
Jupiter's 12-year orbit can be easily tracked as it generally moves
one zodiacal constellation to the east each year. Saturn takes thirty
years to complete its own lap of the sky.
The outer planets set the pulse as they slowly circle the sky, the
inner ones the melody as they flit back and forth.
Frequently two of them will come together in a planetary conjunction,
more occasionally three; all five at once is exceptional. Under the
current favourable circumstances, they will reward an observation on
any clear evening, ideally an hour or so after sunset.
Mars, Venus, and Mercury, with their smaller orbits, faster speeds,
and foreshortened viewing angles, are particularly interesting to follow.
And of course Viewing Platform Earth is moving, too. While we can't
see Earth's orbital motion directly, it is reflected in the position
of the Sun as we go around it. The five planets are all currently on
the far side of the Sun; therefore all six appear to be going in the
same direction -- east against the background stars.
In the upcoming weeks we will see the two inner planets, Mercury and
Venus, pull away from the Sun, as the outer ones seem to fall towards
it. It will be fascinating to watch them group together and overtake
one another.
While Jupiter will continue to stand off to the east (upper left),
the other four will conduct an elaborate square dance over the next
three or four weeks.
Late in April, Mercury will join Venus, Mars and Saturn in the constellation
of Taurus, with all but Saturn passing between the orange giant star
Aldebaran on the left and the famous star cluster, the Pleiades, to
the right.
The richly-studded star field provides a beautiful backdrop to the
planetary dance, especially for those with binoculars.
Come May, first Mars, then Venus will appear to overtake Saturn. Then
the famous pair will two-step through the evenings of May 9 and 10.
May 14 will offer a grand finale of sorts when the slender crescent
Moon, holding the old Moon in its arms, sashays once more past brilliant
Venus, as the fainter members of the planetary troupe fade into the
sunset.
—Bruce McCurdy, Edmonton
BRUCE REMINDS ALL of us that this Saturday, April 20, is International
Astronomy Day, a good time to explore the hobby of stargazing and to consider
joining a chapter of the Royal Astronomical Society of Canada (www.rasc.ca).
A coffee-cup toast to Bruce for helping the rest of us so thoroughly
enjoy the celestial performance!