As September comes to a close, the brilliant planet Venus stands
as the lone planet visible in the eastern morning sky. But that is going to
change in the coming days.
As we transition into October, Venus will soon be joined by
two other planets, Mercury and Saturn. During the first half of October, the
three planets will engage each other in some interesting conjunctions and will
appear to change position relative to each other on a morning-to-morning
basis.
If you have a clear and unobstructed eastern horizon, you'll
be able to follow this interesting dawn dance of the planets.
Binoculars will help because the combination of their low
altitudes and bright morning twilight might make the view a bit challenging at
times. First, we present a viewing synopsis for each planet, followed by a
chronology of the changing array among the three. And as a bonus, the moon
will join them on Oct. 16.
Mercury
During the opening week of October should become easily
visible just above the horizon due east during mid-morning twilight, about 45
to 50 minutes before sunrise. For viewers near 40-degrees north latitude
Mercury is highest on Oct. 5, its date of greatest elongation (18-degrees west
of the sun). While its other five elongations of 2009 are larger in angle, at
this time of year the ecliptic is nearly vertical in the predawn sky for
mid-northern observers.
As a result, Mercury
stands almost directly above the sun and rises right around the time of the
break of dawn. This speedy little planet sinks back toward the sunrise horizon
quite slowly for the rest of October, brightening slightly all the while. By
the third week of October, Mercury becomes difficult to see; superior
conjunction occurs on Nov. 5. A fun challenge will be to follow it as late into
October as possible.
Venus
rises lustrous in the east just before the first gleam of morning twilight
throughout October. Every week Venus sinks a little lower; in the final days of
October binocular viewers may spy the blue star Spica emerging from the dawn
glow well below Venus.
Saturn
is only now emerging into the morning sky in western Virgo and will start
to become visible during the first week of October very low in the east in the
brightening dawn. The rings were turned edgewise to Earth on Sep. 4 and now
the northern ring face is beginning to come into view to our line of sight. In
a telescope magnifying at least 30-power, they'll appear as a thin, bright
line. The angle that Saturn's rings are tipped toward Earth increase slightly
during October from 1.5 to 3-degrees.
Chronology
Oct. 5 – Take note of dimmer Saturn about 3-degrees
below and slightly to Mercury's left this morning.[See Map]
Oct. 8 – Early this morning, a very striking
conjunction takes place between Mercury and Saturn. The two planets will be
separated by only three-tenths of a degree. Mercury will appear almost 5 times
brighter than Saturn, appearing below and to its right. And hovering above and
to their right will be brilliant Venus.
Oct. 13 – Now it's Venus' turn to have a close
conjunction with Saturn. They're separated by only a half-degree; Venus will
sit below and to Saturn's right and will appear nearly 100 times brighter than
its ringed companion.
Oct. 16 – Facing slightly slightly south of due east
this morning about an hour before sunrise, you'll see a slender crescent moon,
less than 2 days before New, forming a broad isosceles
triangle with Saturn and Venus (the moon at the vertex).
Joe Rao serves as an
instructor and guest lecturer at New York's Hayden Planetarium. He writes about
astronomy for The New York Times and other publications, and he is also an
on-camera meteorologist for News 12 Westchester, New York
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