July Moon at Descending Node and a Partial Lunar Eclipse

   Tuesday July 16th the Moon will be crossing 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 day of the node crossing the full Moon will be passing through the Earth’s shadow giving the part of the world where the Moon will be visible a 65% partial lunar eclipse. This will be a penumbral lunar eclipse during which the Moon passes through the fainter outer Earth’s shadow, the penumbra. However the Moon will be passing deeply into the penumbral shadow giving viewers an relatively dark penumbral eclipse lasting more than 2 hours.

   The full Moon rises shortly before midnight July 16th and is about 6-7o to the east from the ringed planet Saturn. The graphic shows how far the Moon has moved from the Earth’s shadow since the end of the Eclipse.

   So where will the eclipse be visible? Not from the U.S. of A. The table below shows eclipse times in UT and a quick conversion to my time zone, U.S.A. Central Daylight Time (CDT=UT-5) shows the eclipse begins at 1:43 pm CDT, maximum is at 4:30 pm CDT, and eclipse ends at 7:17 pm CDT – all times are before the Moon rises for my time zone as well as the rest of North America.

Penumbral eclipse begins: 18:43:53 UT
Partial eclipse begins: 20:01:43 UT
Maximum eclipse: 21:30:43 UT
Partial eclipse ends: 22:59:39 UT
Penumbral eclipse ends: 00:17:36 on 17 Jul UT

   
   
   
   
   

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Moon Along the ecliptic

   As the Earth and Moon orbit the Sun together the Moon follows an orbital path that takes it along the plane of the ecliptic (Earth’s orbit), sometimes above, and sometimes below. At least twice each orbit or during during the calendar period for that orbit the Moon will cross the ecliptic either as an ascending node or a descending node.
   As this short video shows the Moon will follow a path along the ecliptic and as it does so it will pass some of the brighter stars and planets that are arranged on or near the ecliptic.
   You may also notice a steady shift of the sky toward the west. This is the effect of the Earth in motion, revolving, around the Sun. Since the Earth covers the 360o orbit in approximately 365 days the Earth moves almost 1o each day, and the sky in turn has the noticeable westward shift of the same amount.

   
   
   

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Earth at Aphelion – 2019

Earth at Perihelion   Thursday 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 23 UT (6 pm CDT) on Thursday July 4th the Earth is 1.01670 AU (94,508,169 miles; 152,096,155 km) from the Sun.
   Approximately one-half year or one-half revolution earlier, on January 3rd, the Earth was at perihelion, its minimum distance from the Sun for this year (0.9833 AU (91,403,445 miles; 147,099,586 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.
   

   
   
   

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.


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July Moon at Ascending Node

   Wednesday July 3rd the 1.5-day old waxing crescent Moon will be crossing the plane of the ecliptic moving north relative to the ecliptic. 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.

   On the day of the node crossing the thin waxing crescent Moon will be close to the planets Mars and Mercury, however all three are low over the western horizon as the Sun is setting. Since this node crossing was close to the new Moon phase, about 12 hours after, there was a total solar eclipse. Visible from the Southern Hemisphere, Chile and Argentina.

   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)

Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”

   
   
   

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Total Solar Eclipse – Southern Hemisphere Only

   Tuesday July 2nd the new Moon will be about 12 hours away from crossing the plane of the ecliptic, its ascending node. When a node crossing is close to new Moon phase, or full Moon, there will be an eclipse. On July 2nd there will be a total solar eclipse visible throughout the day along a curving path of totality starting southwest of the Pitcairn Islands in the South Pacific Ocean then crossing the Pacific coast of Chile and on to the Atlantic coast of Argentina. The eclipse ends as the Sun is setting for the residents of Buenos Aires.
   Click here to go to the Hermit Eclipse web site for information including a detailed map and eclipse stage times

   
   
   

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Sun Enters Gemini

click on graphic to see it full size   Saturday June 22nd the Sun in its apparent eastward motion along the ecliptic, moves out of the constellation Taurus the Bull and into the constellation of The Gemini Twins. This is the true or actual position of the Sun as opposed to the pseudoscience of astrology which usually has the astrological Sun one constellation ahead or east from the Astronomical Sun’s position.

   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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June 2019 Solstice

   Northern hemisphere spring comes to an end and the summer season begins on Tuesday June 21st at 8 UT (3 am 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 of the Earth’s equator. At this same time the Sun is just entering the boundaries of the astrological constellation Cancer the Crab. Interestingly about 19 hours later, Wednesday June 22nd at 3 UT (10 pm CDT June 21st) the Sun will actually be entering the region of the Gemini Twins as it crosses the boundary between Gemini and Taurus.

   According to the pseudoscience of astrology the Sun, at this date, would be entering the astrological sign of Cancer the Crab.

   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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