Sun Not in Capricornus, but it is the 2017 December Solstice

sag-cap-ani    According to the pseudoscience of astrology the Sun enters the constellation of Capricornus the Sea Goat on Thursday December 21st when in fact the actual position of the Sun is still within the boundaries of the constellation of Sagittarius the Archer.
In reality the Sun will have reached the celestial coordinates of 23.5o degrees south declination; 18 hours right ascension. With regard to the Earth’s surface this places the Sun over the Tropic of Capricorn, which is at 23.5o south latitude. We also know that it is the Earth’s tilt on its axis that is the cause for seasons on Earth rather than the distance between the Earth and the Sun. And of course we know that this signals the start of northern hemisphere winter and the southern hemisphere summer seasons.

The official time for the change of seasons is 1628 UT (1028 am CST).

And for those ‘insanely curious’ like me, while the Sun is at 23.5o South declination and ‘in’ Sagittarius the Earth is opposite at 23.5o North declination and at the feet of the Gemini Twins.

The animated graphic below sets the stage, so to speak, to illustrate the Sun’s actual location with respect to the zodiac constellations in the background. This is as opposed to the location of the Sun according to the pseudoscience of Astrology. The scene is set for 12:15 CST, or mid-day when the Sun is at an azimuth of 180o, or south, and is mid-way between rising and setting. Starting with the Sun at mid-day the scene changes as first the daytime sky is turned off, followed by the horizon being turned off.
   This leaves a sky view like during a total solar eclipse except that the Sun is not blocked out by the new Moon. And like during that solar eclipse the zodiac constellations in the background become visible. Then the following are added starting first with Sagittarius, then Capricorn, and then the ecliptic and celestial equator are added to show the relationship between the two constellations and what makes them plus another 11 constellations the astronomical zodiac of 13 constellations. The animation ends with the addition of the constellation boundary lines and labels for the rest of the constellations in this setting.
It is the ecliptic, the apparent path of the Sun which, if it crosses the boundary of a constellation, makes that constellation one of the zodiac. And during December the Sun’s apparent path takes it across the constellation of Sagittarius rather than Capricorn.

Read a little more about how astrology has the Sun incorrectly placed in a previous blog, and in another blog discussing the effects of precession.

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.

December Solstice 2013

sagittarius-dec21   On Saturday, 21 December, at 11:11 CST (17:11 UT) the Sun will have reached its southernmost distance (in degrees of latitude and/or declination) from the Earth’s surface and celestial equator. Using Geographical coordinates the Sun is over the Tropic of Capricorn at a latitude of 23.5o South. Using Astronomical coordinates the Sun is -23.5o South (declination) and 18Hours RA (right ascension).

December Solstice
seasons   In its annual trek around the Sun the Earth reaches certain orbital positions that define the beginning and end for each of our four seasons. In either hemisphere, northern or southern, we learn these as the spring equinox, summer solstice, autumn equinox, and winter solstice. However the seasons are reversed or the opposite for each hemisphere. Winter in the northern hemisphere, for example, starts when summer in the southern hemisphere begins, and so on. This gives rise to the idea that it may be more practical to simply refer to these dates by the month that it occurs in. So for example rather than saying this is the “winter solstice” and then specifying which hemisphere you are referring to folks in either hemisphere would know which solstice, equinox, and or season it is by simply stating the name of the month for that event, i.e., December Solstice, March Equinox, June Solstice, September Equinox.

Along the Ecliptic
   How are the dates for these changes of seasons selected? As the Earth revolves around the Sun the Sun appears to move eastward against the stars in the background, regardless of the hemisphere. The apparent path the Sun follows is known as the ecliptic and in reality it is the orbit of the Earth superimposed on the stars in the background. seasons on ecliptic-aniAs a rule the starry sky is referred to as the celestial sphere, an imaginary sphere surrounding the Earth on which the ecliptic, stars, planets, and our Moon are located. The Earth’s equator and lines of latitude and longitude are likewise superimposed on the celestial sphere. This is a system similar to the use of latitude and longitude on the Earth’s surface that allows for the positioning or plotting of celestial objects including stars, galaxies, and closer to home the location of the Sun and orbiting planets.

   With regard to the Sun there are specific locations along the ecliptic that mark the change of seasons that correspond to geographic locations on the Earth’s surface. In the northern hemisphere we traditionally say that the Winter Solstice (change to December Solstice) (first day of winter) occurs when the Sun is south of the equator over the Tropic of Capricorn. The Spring Equinox (change to March Equinox) (first day of spring) is when the Sun is over the Earth’s equator. The first day of summer or the Summer Solstice (change to June Solstice) is when the Sun is north of the equator and is over the Tropic of Cancer. And finally when the Sun is back over the Earth’s equator it is the Autumn Equinox (change to September Equinox) and the start of autumn.

Mid-day Sun at 40oNorth

Mid-day Sun at 40oNorth

   These dates are more precisely determined by when the Sun has reached a specific astronomical coordinate on the celestial sphere. However without knowing the calendar date or astronomical position one can easily determine this date by observing the Sun’s apparent daily path regularly.
   In the northern hemisphere on the first day of winter during December the Sun will be south of the equator and will follow the shortest apparent path from east to west. It will rise in the southeast at its furthest south point from due east and set in the southwest at its furthest south point from due west. Midway between rising and setting the Sun will be at its lowest mid-day point above the southern horizon. In contrast it is the start of summer in the southern hemisphere during December. From those latitudes the Sun will follow its longest apparent path from east to west. The Sun will rise in the southeast at its furthest south point from due east and set in the southwest at its furthest south point from due west. Midway between rising and setting the Sun in the southern hemisphere would be at its highest mid-day point above the northern horizon.

The View From South of the Equator
   Keep in mind that these observations are based on the direction one typically faces to view the apparent path of the Sun follows between rising and setting. This direction is always toward or relative to the Earth’s equator and is centered mid-way between due east and due west. It is also latitude-dependent in that the length of daylight and night varies with latitude – more hours of daylight close to the equator where the Sun’s apparent path takes it higher above the horizon and subsequently giving more time above the horizon. Moving away from the equator the Sun’s apparent path doesn’t take it as high above the horizon and thus less daylight time. Nonetheless those in the northern hemisphere face toward south while those in the southern hemisphere face toward north. Remember – the Sun and all other celestial objects always rise in the east!

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.