Monday, September 19, 2005

Return of the Long Nights

Return of the Long Nights
by Dave Adalian

Summer is taking an early departure this year, folding away her brown mantle and allowing the cool days and chill nights of autumn to come quickly as the leaves begin to fall.

This is fitting as (on Sept. 22, 2005) at 2:23 p.m. PDT the Sun crosses south of the celestial equator, reaching equinox and marking the moment when autumn begins and the days shorten while nights grow long and cold.

When the Sun sets this evening, it will fall directly west and rise again tomorrow due east, silhouetting the crags of the Sierra Nevada. Though the periods of light and dark won’t be perfectly equal as the Latin term equinox implies, the time between sunset tonight when half the Sun’s disk is below the horizon and sunrise tomorrow when half the disk is above the horizon will be just eight minutes shy of 12 hours.

The equinox is the moment when the Sun crosses the dividing line that splits the sky into two equal northern and southern halves, creating some special effects here on Earth.

At the equator on the days of the March and September equinoxes, the Sun not only rises and sets at the points of true east and west, it also passes directly overhead when it reaches its highest point in the sky, something it never does at more northern or southern latitudes.

At the poles, the effect is far more dramatic.

At the North Pole, the September equinox signals a plunge into six months of darkness, with the Sun dropping below the horizon not to be seen again until the end of March.

On the bottom of the planet, the effect is reversed, with the Sun finally returning to the sky for six uninterrupted months of daylight. Instead of rising and falling as it does elsewhere, during the months-long period of day the Sun skims along the icy horizon, climbing higher in the sky as the solstice approaches.

Were it not for the killing cold of the arctic winter, the North Pole would be a Moon-lover’s delight. During the six-month darkness, the Moon rises above the horizon not to set again for two weeks. The Moon moves through its cycle in unashamed plain sight before dipping again below the horizon for a fortnight’s absence.

Late Sept. 21 and 22 here at home, the Moon will put on a beautiful display in the east, joining the Seven Sisters of the Pleiades, the V-shape of the Hyades and a bright and ruddy Mars.


Join the Tulare Astronomical Association for a public star party this Friday, Sept. 23, 8:30-10:30 p.m. at the Arthur L. Purcell Observatory, 9242 Ave. 184, south of Tulare and 2.1 miles west of Highway 198.


RomRod said...

Sep 22, 2005, 22:23 UT, autumn equinox, is this the same equinox your say occurred today? best regards from a reader in Venezuela!

Dave said...

My column appears in the local newspaper, where this particular edition will be published Thursday, Sept. 22. Thanks for your note. I've made it more clear, and will add a note once the column has been published offline.

Also, the 2:23 p.m. I referred to is Pacific Daylight Time (PDT).

-- Dave

RomRod said...

ohh now I get it. Excellent idea of having a column in a newspaper. So much astrology nonsense these days, columns like yours is something we do need here where I live...