Monday January 20th at 9 UT the Sun in its apparent eastward motion along the ecliptic enters the boundaries of the constellation Capricornus the Sea Goat. This is the actual location of the Sun.
Interestingly, according to the pseudoscience of astrology, 6 hours later, at 15 UT Monday January 20th, the Sun should be entering the constellation of Aquarius the Water Bearer.
Feel the Heat?
Sunday January 5th at 8 UT (3 am CST), as the Earth continues its annual trek around the Sun, the Earth reaches a point in its orbit that is called perihelion. Perihelion is the minimum distance that separates the Earth from the Sun, and we are the closest to the Sun for the year at this point in the orbit. So this year, 2020, the Earth is 0.9832 AU (91,398,199 miles : 147,091,144 km) from the Sun.
Approximately one-half year or one-half revolution later, on July 4th, the Earth is at aphelion and is 1.01669 AU (94,507,634 miles; 152,096,155 km), its maximum distance from the Sun for 2020. This approximately 3% difference in distances between perihelion and aphelion is due to the shape of the Earth’s orbit being elliptical rather than circular. However the Earth has a mildly elliptically shaped orbit that is closer to being slightly out-of-round than the incorrect, very elliptical orbit that is often shown – like the illustration used here.
In Astronomy the shape of a planet’s orbit is called eccentricity, with 0 being a circle and 1 a straight line. Any value between 0 and 1 represents an ellipse. The shape of the Earth’s orbit is so close to being circular that the apparent size of the Sun does not appear to change as this animated graphic shows. The difference between perihelion and aphelion is about 3%.
Eccentricity for each planet is listed below for comparison.
Planet Eccentricity Mercury 0.2056 Venus 0.0068 Earth 0.0167 Mars 0.0934 Jupiter 0.0484 Saturn 0.0542 Uranus 0.0472 Neptune 0.0086 Pluto 0.2488
To read more about the Earth’s orbit and get some teaching ideas click here to download a PDF copy of my January 2011 Scope on the Skies column “Solar Explorations“.
Here is a good classroom activity about the Earth’s orbit and its effect on the apparent size of the Sun: Why Does the Size of the Sun Appear to Change? A Year of the Sun.
Friday January 3rd Mars and Uranus will reached their respective orbital positions that have them 180o apart. Mars will be located at approximately 215.3o and Uranus at approximately 35.3o of heliocentric longitude. This called heliocentric opposition.
For the past several months the outer planets Jupiter and Saturn have been the brightly shining ‘evening stars’ over the western horizon at sunset. They have recently been joined by the inner planet Venus, but at the same time as Venus has become more prominent each evening Jupiter and Saturn have been setting earlier as they gradually move closer to the horizon at sunset.
And now Jupiter is no longer in the ‘picture’. So what happened to Jupiter, and will soon happen to Saturn? All solar system objects orbiting the Sun beyond Earth’s orbit move at a slower pace around the Sun than the Earth. The Sun has an apparent motion toward the east which is the same as the Earth’s actual motion. So what happens is that over time the Sun catches up with Jupiter, then Saturn. Eventually the Sun passes them and the planets become visible in the morning skies rising ahead of the Sun.
At some point along their respective orbital path they will be on the opposite of the Sun from the Earth. This is known as solar conjunction, and that is where Jupiter will officially be on Friday December 27th.
Thursday December 26th the Moon, at new Moon phase, crosses the plane of the ecliptic moving south. This is known as the descending node, one of two intersections the Moon’s orbital path (dark green line) has with the ecliptic.
What happens when the Moon is at new phase and is also at a node crossing? You get an eclipse of the Sun, which in this instance will be an Annular Solar Eclipse. This is a solar eclipse however the Moon is far enough from the Earth that it appears to be smaller than the Sun. So, unlike with a Solar Eclipse where at mid-eclipse the Moon’s disk covers the Sun’s disk, during mid-annularity the Moon’s disk does not completely cover the disk of the Sun but instead leaves a ‘ring of fire’ known as the annulus around the Sun.
This eclipse will be visible from Saudi Arabia to south of the Philippine Islands.
Note: The picture I used for the banner is of the 2011 Annular Eclipse and it is from the NASA Hinode satellite. Also at the NASA web page the link takes you to is a video of the Annular Solar Eclipse as seen from the satellite in Earth orbit.
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Tuesday evening December 24th around sunset or after the skies darken look toward the western horizon and you can’t miss noticing the bright celestial object – the inner planet Venus. Also, despite the fact that we are now two seasons away from our summer (Northern Hemisphere), over the western horizon are three stars making up the ‘Summer Triangle’. These three stars each belong to a seperate constellation but together they form an asterism,not a constellation, but a recognizable star shape.
Wednesday morning December 25th look toward the eastern horizon for the ‘Red Planet’ (Mars) to be above the horizon and about 15o from the reddish star Antares in Scorpius the Scorpion. In this graphic Antares is just above the horizon.
Higher above Mars, toward the right or the west, is a the bluish star Spica in Virgo the Harvest Maiden. And higher still but toward the left is another reddish star. This is Arcturus in Bootes the Herdsman.
As this year and decade come to a close I’d like to thank all my readers and the universe in general for allowing me an opportunity to share things celestial.
Have a happy and safe Holiday however you celebrate.
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According to the pseudoscience of astrology the Sun enters the constellation of Capricornus the Sea Goat this month when in fact the actual position of the Sun is still within the boundaries of the constellation of Sagittarius the Archer.
In Astronomic terms the December Solstice is official when 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 at 4:21 UT on Sunday December 22nd, or 10:21 pm CST Saturday December 21st.
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.