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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Waxing Crescent Moon on the Move

   Shortly after sunset local time on July 3rd look toward the western horizon for the 1.5-day old thin waxing crescent Moon to be close to the planets Mars and Mercury, and within about 4-5o from Pollux, one of the Gemini Twins stars.
   The following evening, July 4th, the 2.5-day old waxing crescent Moon will have moved about 15o further toward the east and will be about 3-4o from the open star cluster, M-44. Also known as the ‘Beehive Cluster’ it is a group of stars around 600 light years away and visible to the naked eye as a small ‘smudge’ of light with an apparent magnitude of around 3.70.
   Both the Moon and M-44 will easily fit within the field of view of binoculars.

   
   
   

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?”

   
   
   

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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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

   
   
   

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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Waning Crescent Moon and Open Star Clusters

   Sunday morning June 30th, before sunrise local time, look for a thin 27-day old waning crescent Moon to be close to the two open star clusters in Taurus the Bull, the Pleiades and the Hyades. The Pleiades are about 9-10o west, or above, the Moon, while the v-shaped Hyades and the Moon will all fit within the field of view of binoculars.

   
   
   

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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Waning Crescent Moon Passes Uranus

   Thursday and Friday mornings before the Sun rises look toward the eastern horizon for the 24-day old waning crescent Moon to be within about 8-9o to the west from the outer ringed planet Uranus on Thursday the 27th, and about 7-8o from Uranus but now to the east on Friday the 28th.


   Uranus has an apparent magnitude 5.84 which technically makes it naked-eye visible (in dark skies) however nearby is the thin waning crescent Moon outshining Uranus with a -11.00 apparent magnitude. Worth mentioning but not naked eye visible is the outermost of the 8 planets, Neptune, with a 7.90 apparent magnitude.

   
   
   

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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June Moon at Apogee

   Our Moon reaches apogee, (greatest distance from Earth), for this orbit, on Sunday June 23rd. At that time the Moon will be at a distance of 31.71 Earth diameters 251,374 miles (404,548 km) from the Earth.

   The 20-day old waning gibbous Moon rises around midnight local time and sets later that same day.

   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)

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

   
   
   

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


Also Follow me and other great resources at Feedspot.