Monday, December 21, 2015

Winter & SpaceX Launch w/ Web-Cast Tonight; Ursid Meteors Peak Dec. 22

http://buhlplanetarium.tripod.com/pix/graphics/solsticeimage008.png
This graphic generally shows the location and configuration of the Earth, in relation to the Sun, during the time of Solstices and Equinoxes during the year.
(Image Source: ©1999, Eric G. Canali, former Floor Manager of Pittsburgh's original Buhl Planetarium and Institute of Popular Science and Founder of the South Hills Backyard Astronomers amateur astronomy club; permission granted for only non-profit use with credit to author.)

By Glenn A. Walsh
Reporting for SpaceWatchtower

The season of Winter officially begins late this evening in the Northern Hemisphere of Earth, at the moment of the Winter Solstice, on Monday Evening, 2015 December 21 at 11:48 p.m. Eastern Standard Time (EST) / December 22 at 4:48 Coordinated Universal Time (UTC); at the same time, the season of Summer begins in the Southern Hemisphere. A day later, the annual Ursid Meteor Shower peaks.

Also, the SpaceX Falcon 9 rocket will be launched from Cape Canaveral this evening, after being postponed from last evening. And, about ten minutes after the 8:33 p.m. EST / Dec. 22 1:33 UTC launch, SpaceX will make their first attempt to land the first-stage of the Falcon 9 rocket, in an upright position, on solid ground—back at the Cape Canaveral launch site.

Both previous attempts at a first-stage landing (on a barge in the ocean) failed, but SpaceX CEO Elon Musk is confident that the problems from the first two attempts have been rectified. If the landing is successful, this will be a milestone in the goal of making these rockets re-usable.

However, the primary goal of this mission is to deliver 11 satellites into orbit for a world-wide communications company called ORBCOMM. This will be the first SpaceX launch since the explosion, after launch, of a Dragon cargo spacecraft bound for the International Space Station six months ago.

An Internet web-cast of the launch will be available. An Internet link to this web-cast is located at the end of this blog post.

                                       Winter Solstice 2015     

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. Mid-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 (the actual birth date probably occurred in August or September).

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) around December 21, this marks the Winter Solstice in the Northern Hemisphere (and the Summer Solstice in the Southern Hemisphere).

 

Alternately around June 21, 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.

The day of the December Solstice is the only time of the year when local Noon actually occurs at the South Pole. Conversely, it is also the only time of the year when local Midnight occurs at the North Pole. And, of course, it is the reverse during the June Solstice: the North Pole reaches local Noon for the only time in the year, while the South Pole reaches local Midnight for the only time in the year.

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. For this reason, Homeless Persons' Memorial Day is commemorated on December 21.

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.

                                                Ursid Meteor Shower

Almost 24 hours after the Winter Solstice, on 2015 December 22 at 9:00 p.m. EST / December 23 at 2:00 UTC, comes the peak of the Ursid Meteor Shower, which actually begins on December 17 and usually lasts about a week ending December 24, 25, or 26. The Ursids seem to comprise a narrow stream of debris originating from Comet Tuttle. Hence, it is difficult to see Ursid meteors outside of a 12-hour window before and after the peak, where possibly 12 meteors per hour could be seen.

The Ursid Meteor Shower is 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 (better known as the asterism the "Little Dipper"), which is the brightest star in the bowl of the Little Dipper. Some people call these meteors "Umids," in an attempt to emphasize that their apparent radiant is Ursa Minor, not Ursa Major (the asterism the “Big Dipper”).

However, you should not, necessarily, be looking only at the Little Dipper when looking for meteors in this shower. Meteors can appear in any part of the sky at any time (although a meteor's trail may tend to point back toward the radiant).

Of course, meteor showers. like all celestial observations, are weather-permitting. If there are more than a very few clouds in the sky, meteors will be much more difficult to find. Clear skies are something not always available in the skies of late Autumn and early Winter. And, it is always best to get away from city lights, for the opportunity to see the smaller, dimmer meteors. As always, the best time to view any meteor shower is between local midnight and local dawn, when the Earth is actually rotating into the stream of meteoric debris.

Binoculars and telescopes are not very useful for finding meteors. Meteors streak across the sky in a very short period of time, far too short to aim binoculars or a telescope. So, the best way to view a meteor shower is to lie on a blanket or beach towel on the ground, or use a reclining chair, in an area with a good view of the entire sky (with few obstructions such as buildings, trees, or hills), and keep scanning the entire sky.

So, if you go out to see the Ursid Meteor Shower, start looking for meteors around local midnight, or perhaps a little later. Make sure you have a good site where you can see most of the sky, and that sky is relatively clear. Be sure to dress properly for the early morning temperatures, now that Winter has just begun.

And, you want to go out ahead of time, before you actually start looking for meteors, to get your eyes accustomed to the dark sky. Dark-adapting your eyes for meteor-watching could take up to a half-hour.

More on the SpaceX Falcon 9 Rocket: Link >>> https://en.wikipedia.org/wiki/Falcon_9

SpaceX Falcon 9 Launch Internet Web-Cast: Link >>> https://livestream.com/spacex

More on the Winter Solstice:
Link 1 >>> http://scienceworld.wolfram.com/astronomy/WinterSolstice.html
Link 2 >>> http://en.wikipedia.org/wiki/Winter

More on a Solstice: Link >>> http://en.wikipedia.org/wiki/Solstice

Popular Winter Planetarium Sky Shows Shown at Pittsburgh's original Buhl Planetarium and Institute of Popular Science (1939 to 1991), including full scripts of each show:
The Star of Bethlehem >>> http://buhlplanetarium3.tripod.com/skyshow/bethlehem/
The Stars of Winter >>> http://buhlplanetarium3.tripod.com/skyshow/winter/

More on calendars ---
       Gregorian Calendar: Link >>> http://en.wikipedia.org/wiki/Gregorian_calendar
       Julian Calendar: Link >>> http://en.wikipedia.org/wiki/Julian_calendar

More on the Ursid Meteor Shower: Link >>> http://en.wikipedia.org/wiki/UrsidsA

More on the Homeless Persons' Memorial Day: Link >>> http://www.hchmd.org/memorialday.shtml

Related Blog Post ---

"NASA Orders SpaceX Astronaut Launches." 2015 Nov. 22.

Link >>> http://spacewatchtower.blogspot.com/2015/11/nasa-orders-spacex-astronaut-launches.html


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

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gaw

Glenn A. Walsh, Project Director,
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* Adler Planetarium, Chicago:
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* Astronomer, Educator, Optician John A. Brashear:
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