Saturday, December 21, 2013

Winter Begins Sat.; Ursid Meteor Shower Peaks Sun. w/ Web-Cast


Sunrise viewed between the stones at the ancient Stonehenge astronomical observatory in southern England, on the Winter Solstice in 1985. (Image Source: )

By Glenn A. Walsh
Reporting for SpaceWatchtower

The season of Winter begins in Earth's Northern Hemisphere at the moment of the Winter Solstice on Saturday Afternoon, 2013 December 21 at 12:11 p.m. EST (17:11 Coordinated Universal Time). At the same time, the Summer Solstice marks the beginning of the season of Summer in the Southern Hemisphere.

The annual Ursid Meteor Shower peaks the next morning at 9:00 a.m. EST (14:00 Coordinated Universal Time). An all-night long web-cast of this meteor shower will be available, beginning early Saturday evening.

                                     Winter Solstice 2013

In etymology, the word solstice comes from the Latin terms sol (Sun) and sistere (to stand still). In ancient times, astronomers / astrologers / priests recognized that one day of the year the Sun would appear to reach its lowest point in the sky for the year. The motion of the Sun's apparent path in the sky (what is known astronomically today as the Sun's declination) would cease on this day, before reversing direction.

With our current Gregorian Calendar, this usually occurs on, or very close to, December 21. In ancient times, when people used the Julian Calendar, the Winter Solstice occurred on, or very close to, December 25, what we now know as Christmas Day. Winter festivals, at the time of the Winter Solstice, were common in ancient times. Instead of competing with these traditions, the early Roman Catholic Church christianized the Winter festivals by observing the birth of Jesus Christ on December 25.

Today, we know that, while the Sun does have motions, it is actually the motion of the Earth, tilted on its axis 23.44 degrees while revolving around the Sun, that causes the Earth's seasons. Hence, as the Earth arrives at the point in its orbit around the Sun, when the south polar axis is most directly inclined toward the Sun (thus, the Sun appears at its lowest point for the year in the Northern Hemisphere sky), this marks the Winter Solstice in the Northern Hemisphere (and the Summer Solstice in the Southern Hemisphere).

Alternately, the Summer Solstice marks the beginning of Summer in the Northern Hemisphere (and the Winter Solstice begins Winter in the Southern Hemisphere) when the Earth reaches the point in its orbit when the north polar axis is most directly inclined toward the Sun.

Although the Winter months in the Northern Hemisphere are known for the year's coldest weather, the Earth is actually at the point in its orbit closest to the Sun (astronomically known as the point of perihelion) on or very near January 2. The Earth is farthest from the Sun, each year shortly after the Northern Hemisphere's Summer Solstice, on or very near July 5 (the point of aphelion).

Solar radiation, and hence heat from the Sun, depends on the length of daylight and the angle of the Sun above the horizon. The tilt of the planet's axis toward the Sun determines the additional and more direct solar radiation received by a planet's northern or southern hemisphere, and hence, the warmer season of the respective hemisphere.

The Winter Solstice is known as the "shortest day of the year" and the "longest night of the year" as the Sun shines on the Northern Hemisphere for the shortest length of time for the entire year, on this day.

Interestingly, the climate of a locale in the Southern Hemisphere is, on average, slightly milder than a location at the same latitude in the Northern Hemisphere, because the Southern Hemisphere has significantly more ocean water and much less land. Water warms-up and cools-down more slowly than does land. The only exception is the Antarctic which is colder than the Northern Hemisphere's Arctic region.

The Vernal Equinox, in the Northern Hemisphere when Spring begins (coinciding with the Autumnal Equinox in the Southern Hemisphere when Autumn or Fall begins), occurs between the Winter and Summer Solstices when the Earth reaches the point in its orbit around the Sun when the Earth's axis is tilted neither toward nor away from the Sun. Likewise, when the Earth reaches the point in its orbit around the Sun when the Earth's axis is inclined neither toward nor away from the Sun, between the Summer and Winter Solstices, this is known as the Autumnal Equinox when Autumn or Fall begins in the Northern Hemisphere (Vernal Equinox when Spring begins in the Southern Hemisphere). And, half-way between the beginning points of each season are Cross-Quarter Days, related to the traditional holidays of Groundhog Day, May Day, Lammas Day (traditionally, the first harvest festival of the year on August 1), and Halloween Day.

Homeless Persons' Memorial Day is now observed on the Winter Solstice, by the National Coalition for the Homeless and the National Health Care for the Homeless Council. As many of the homeless spend their nights on the streets, this remembrance is purposely scheduled for the longest night of the year.

                           Ursid Meteor Shower 2013

About a day after the Winter Solstice, each year, comes the peak of the Ursid Meteor Shower, which begins around December 17 and could last until December 24, 25, or even 26. However, the Ursids seem to be a narrow stream of debris originating from Comet Tuttle, so it is difficult to see Ursid meteors outside of a 12-hour window before or after the December 22 peak. At the peak, the Ursid Meteor Shower can produce about 12 meteors per hour.

Clear skies are always a must for meteor viewing, something not always available during the early Winter skies. And, it is always best to get away from city lights, for the chance to see the dimmer meteors.

As always, the best viewing for a meteor shower is between local midnight and local dawn, when the Earth is rotating into the meteor shower. However, a nearly Full Moon (waning gibbous, with 77 percent of the Moon's visible surface illuminated by the Sun) will hinder meteor viewing this year. It could be possible to view some meteors in the early evening of December 21 after sunset and before moonrise (for the evening of December 21 in Pittsburgh, sunset will be 4:57 p.m. EST, moonrise at 9:13 p.m. EST); however, as already noted, this is not the optimal time for viewing a meteor shower.

The Ursids are so named because most meteors appear to radiate from a point near the Star Beta Ursae Minoris (apparent meteor shower radiant) in the Constellation Ursa Minor (“Little Dipper”), which is the brightest star in the bowl of the Little Dipper. However, during any meteor shower, meteors can appear in any part of the sky at any time.

Telescopes and binoculars are of little use for finding meteors. Such optical devices restrict the field-of-view, thus a viewer could easily miss a lot of meteors. The chance of viewing a meteor with a telescope or binoculars is not very good. The best way to look for meteors is to lie down on the ground, in an area with an unobstructed view of most of the sky. Then, just keep scanning throughout the sky until you see a meteor.

For areas such as Pittsburgh, where the weather may preclude direct viewing of this meteor shower this year, a live web-cast of the event will be available on the < > Internet web site, all-night long beginning Saturday Evening (December 21) at 5:30 p.m. EST (22:30 Coordinated Universal Time).

More on the Winter Solstice:
Link 1 >>>
Link 2 >>>

Popular Winter Planetarium Sky Shows Shown at Pittsburgh's original Buhl Planetarium and Institute of Popular Science (1939 to 1991):
The Star of Bethlehem >>>
The Stars of Winter >>>

More on the Ursid Meteor Shower: Link >>>

All-Night Web-Cast (December 21 to 22) of Ursid Meteor Shower:
Link >>>

Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss.

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Glenn A. Walsh, Project Director,
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Author of History Web Sites on the Internet --
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* Andrew Carnegie & Carnegie Libraries:
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* Civil War Museum of Andrew Carnegie Free Library:
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* Duquesne Incline cable-car railway, Pittsburgh:
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* Public Transit:
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