Walter Mencken 11 a.m., May 24
The Vernal Equinox, Saturn, and the Big Dipper
The Vernal Equinox on Saturday, March 20 at 10:32am Pacific daylight time heralded the beginning of the spring season for Earth's northern hemisphere. At the instant of vernal equinox, the sun lied in the plane of Earth's equator. As a consequence, days and nights are of equal length (12 hours each) everywhere on our planet. Another consequence is that the sun rises due east along the horizon and sets due west. During the next three months, as the sun shines more and more directly on our hemisphere, daylight hours will lengthen and the rise and set positions of the sun will gradually shift toward the northeast and northwest, respectively.
Saturn lies at opposition to the sun on Sunday, March 21. Look for this creamy white planet over the east horizon as evening twilight gathers any day this week or next. Saturn remains in the sky all night currently, rising at sunset and setting at sunrise. It will remain a good telescopic target for the next three or four months. Saturn's rings are currently tilted only a few degrees to the line of sight (nearly edge-on); though they will gradually open up to nearly 30 degrees inclined some seven years from now.
The Big Dipper, an abbreviated version of the larger constellation known as Ursa Major (the Great Bear), hovers nearly straight overhead during evening hours from March through June. The seven stars of the dipper -- all but one classified as "second magnitude" in brightness -- can be distinctly seen on clear evenings, even from light-polluted city locations. The two stars at the end of the bowl of the Big Dipper point downward toward a lone, second-magnitude star: Polaris, the North Star, which perpetually marks the direction of true north.
More like this:
- Sunday's Saturn and Sun Opposition — April 1, 2011
- The Big Dipper, the Planet Venus — March 26, 2011
- The Moon, the Tides, and the Vernal Equinox — March 17, 2011
- Autumn Arrives — Sept. 21, 2009
- Vernal Equinox, Sage, Yucca, India Hawthorn, and the Big Dipper — March 19, 2009