Earth at aphelion – 2020

   Saturday July 4th, as the Earth continues its annual trek around the Sun, the Earth reaches a point in its orbit that is called aphelion. Aphelion is the greatest distance that separates the Earth from the Sun, and we are the furthest from the Sun for the year at this point in the orbit. So, at 12 UT (7 am CDT) on Saturday July 4th the Earth is 1.0167 AU (94,507,635 miles, 152,095,295 km) from the Sun.
   Approximately one-half year or one-half revolution earlier, on January 5th 2020, the Earth was at perihelion, its minimum distance from the Sun for this year at 0.9832 AU (91,398,199 miles : 147,091,144 km). This difference, about 3%, in distances 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.
sun2014-ani   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.
   

   
   
   

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July Moon at Descending Node

   Friday July 3rd the 11-day old waxing gibbous Moon 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.

   On the date of the descending node the waxing gibbous Moon will be over the southern horizon around local time for sunset. Look for the Moon to be about 9-10o from the heart of Scorpius the Scorpion, the reddish star Antares.

   
   
   
   
   

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Mercury at Inferior Conjunction

   Wednesday July 1st the innermost planet Mercury reaches inferior conjunction. At inferior conjunction Mercury will move between the Earth and the Sun – much like the position of the Moon at new phase. The graphic to the right shows the planet positions relative to the Earth and Sun for both inner planets and outer planets.

   At this inferior conjunction Mercury will not be directly in line with the Earth and the Sun – on the ecliptic. Mercury has an orbital inclination of 7o with respect to the ecliptic. So like our Moon, Mercury during each complete orbit, will cross the plane of the ecliptic moving north (ascending node) and also moving south (descending node). For this inferior conjunction Mercury will be south of the ecliptic, by about 5.47o.

   
   
   

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June Moon at Perigee

   Our Moon reaches perigee, (closest to Earth), for this orbit, on Tuesday June 30th. At that time the Moon will be at a distance of 28.92 Earth diameters, 229,259 miles (368,958 km) from the Earth.

   On the day of the perigee Moon the 10-day old waxing gibbous Moon will be over the southeastern horizon around mid-evening.

   Does our Moon actually go around the Earth as this graphic shows? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*
   *Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

   
   
   
   
   
   

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Virgo Spikes the Moon

   Our Moon, after traversing the boundaries of the constellation Leo the Lion, will then do a similiar crossing of the constellation Virgo the Harvest Maiden. Roughly midway across Virgo is the bright blue-white star Spica. From mythologies the star Spica represents a harvested bundle of grasses, maybe wheat or oats.
   On the evening of June 28th the Moon will be about 7o to the west from Spica, and the next evening, June 29th the Moon will about 9-10o to the east from Spica.

   
   
   

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Leo and the Moon

   The next several evenings, as our Moon waxes through its phases, the Moon will pass by some familiar celestial objects – stars, star clusters, and planets. They all have something in common, that being that these objects are near the ecliptic. Our Moon follows the ecliptic in a more or less parallel path assuming that parallel paths may be bent! The Moon’s orbit is inclined or tilted about 6o from the ecliptic meaning that the Moon will at times be above, below, or on the ecliptic.
   So with the above in mind on the evenings of June 24th and 25th the 3 to 5-day old waxing crescent Moon will be passing by the heart of Leo the Lion, the bright star Regulus. As you can see from the graphic above Regulus lies nearly on the ecliptic.

   
   
   

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Thin Moon on the Move

   Sunday June 21st, on the other side of the Earth from the U.S.A., the new Moon will be passing between the Earth and the Sun giving that side of the world an annular solar eclipse.
   About 1/2-day later the just past new Moon, an 0.80-day young thin waxing crescent Moon may be seen just above the western horizon at sunset local time. If you see the Moon look closely for a star-like object just to the left from the Moon. This is the inner planet Mercury.
   If you miss the Moon and Mercury on Sunday evening wait until Monday evening June 22nd to see the still thin 1.85-days old waxing crescent Moon near one of the Gemini ‘Twin’ stars, Pollux.
   Not had enough? On Tuesday June 23rd the 2.80-days young waxing crescent Moon will be near M44, the Beehive Cluster.
   Any of these conjunctions will look great in binoculars.

   
   
   

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June Moon at Ascending Node and a Solar Eclipse

   Sunday June 21st the new Moon will be crossing the plane of the ecliptic moving north. This is known as the ascending node, one of two intersections the Moon’s orbital path has with the ecliptic. The ecliptic is actually the Earth’s orbit, and the Moon’s orbit is inclined about 6o from the ecliptic. So there are two node intersections, the ascending and descending nodes.
   Whenever our Moon at either new or full phase crosses the plane of the ecliptic, a node crossing, there will be an eclipse of the Sun with a new Moon, or a lunar eclipse with the full Moon phase. On the 21st the new Moon will be aligned with the Sun for a solar eclipse. (Not visible from North America) However this solar eclipse is an annular solar eclipse, where at mid-eclipse the Moon does not completely cover the Sun. There is no ‘diamond bead’ effect, no corona like what is seen with a total solar eclipse. This is because the Moon and our Sun appear to be about the same size in the sky with the exception that the Moon’s orbit is more elliptical than the Earth’s orbit around the Sun. This means that the Moon can be closer or further away during a solar eclipse. With this annular solar eclipse the Moon is further away, appears smaller than the Sun, and at mid-eclipse leaves an annulus, a ‘ring of fire’ around the Sun as this animated graphic is showing.
Note, I have brightened the side of the Moon facing toward us. During a solar eclipse we would only see a silhouette of the Moon.

   Does our Moon actually go around the Earth as many graphics show? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*
*Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)


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June Solstice – 2020

   Northern hemisphere spring comes to an end and its summer begins on Saturday June 20st at 21:45 UT (4:45 pm CDT) when the Sun ‘reaches’ the celestial coordinates of 23.5o north declination and 6 hours right ascension. With respect to the Earth’s surface the Sun is described as over the Tropic of Cancer, 23.5o, north latitude of the Earth’s equator. At this same time according to astrology the Sun is said to be entering the boundaries of the astrological constellation Cancer the Crab. Actually it is not. Interestingly about 7 hours later, June 21st at 9 UT (4 am CDT) the Sun will actually be entering the region of the Gemini Twins as it crosses the boundary between Gemini and Taurus.

   We know that it is the Earth’s orbital motion around the Sun that causes the sun’s apparent eastward motion among the stars in the background. This is how the Sun ‘reaches’ a celestial coordinate, how it ‘crosses’ the boundaries between constellations, or how it is ‘in’ a constellation.

   With respect to the southern hemisphere this is the end of their summer and start of their fall season. So thinking globally my preference has been to use the name of the month to designate the season change. Hence the use of the term June Solstice rather than summer solstice.

   
      
   

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Sun Not Really In Cancer

   According to the pseudoscience of astrology the Sun enters the constellation of Cancer the Crab on Sunday June 21st at 9 UT (4 am CDT). When in fact the actual position of the Sun on this date is still within the boundary of the constellation of Taurus the Bull, but by very little. The Sun is very close to the eastern boundary for Taurus and the western boundary for the Gemini Twins, as this graphic and the banner graphic at the top of the page shows.
   Interestingly the June solstice was yesterday
   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.
   
   
   
   

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