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.
   

   
   
   

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 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.

   
      
   

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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Sun Enters Taurus the Bull – 2020

   Wednesday May 13th the Sun in its apparent eastward motion along the ecliptic, moves out of the constellation Aries the Ram and into the constellation of Taurus the Bull. 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.


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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March Equinox – 2020

   Friday March 20th, this year-2020, is an equinox day. However depending on your local time zone the equinox may occur on the day before as the official time for the equinox is 03:54 UT on the 20th which for my time zone is 10:54 pm March 19th. Regardless, for those in the northern hemisphere winter is ending and spring has ‘sprung’ (starts). From a geographical perspective we would describe the Sun as being over the Earth’s equator, and as this graphic shows there would be an equal amount of daylight and night on our planet as a result.
    At mid-day on the equator the sun is directly overhead and from that latitude you have no elongated shadow, just a ‘blob-like’ shadow at your feet as this picture of my feet taken at mid-day in Quito Ecuador shows.

    Regardless of your hemispheric preference get outside and cast a shadow!

  Northern hemisphere spring officially (well at least astronomically) begins at 03:54 UT on the 20th which for my time zone is 10:54 pm March 19th when the Sun reaches the celestial coordinates of 0 hours and 0 degrees as it moves northward along the ecliptic crossing the celestial equator. At this location the Sun is just within the constellation of Pisces the Fishes and not entering Aries the Ram as the pseudoscience of astrology would have you believe.

    To learn more about the celestial coordinates click here to read a previous post about seasons and the equinox.

   Click here to see the online world sunlight map used to make the day/night graphic at the top of the page.


   Celebrate Solar Week March 23rd-27th. Click here to go to the Solar Week web site.

   
   
   
   During a trip to Quito Ecuador to visit one of the exchange student we had hosted, and her family, we spent the day at a Museum on the equator, Mitad del Mundo. I brought along my over-sized protractor knowing in advance that we would be at the museum. So at mid-day I had my wife stand on the equator (yellow line) and hold a string to the top of her head while Cathy, a sister of our exchange student, held the protractor. This was done during the summer so the Sun was over the northern horizon at mid-day and the Sun’s angle above the northern horizon was around 75o.

   Here is a short series of hourly pictures taken during the day on the September equinox on the equator in Quito Ecuador at Collegio Menor San Francisco de Quito, a private school that I visited and did the SunShIP project with (Sun Shadow Investigation Project).

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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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Saturn at Solar Conjunction – 2019

   Monday January 13th the planet Saturn will have reached the astronomical coordinates that officially place it at solar conjunction. From our perspective the planet is behind the Sun, or on the opposite side of the Sun from the Earth.

   In reality it is not as much as Saturn moving behind the Sun as it is the Sun passing in front of Saturn – or so it seems. As a distant outer planet Saturn moves more slowly around the Sun than the Earth does. One year on Saturn is equal to 29.7 years (10,832 days) on Earth. So in one Earth day Saturn would travel how much of the 360o orbit around the Sun? That would amount to approximately 0.033o each day.

   The Sun, in its apparent motion along the ecliptic moves at the rate the Earth is moving which is 0.99o each day. So with the Sun’s apparent motion (0.99o/day) it quickly, relative to Saturn, passes Saturn while both are moving eastward. This animated graphic starts with Saturn and the Sun above the horizon a couple of hours after sunrise. The animation is set for 1-day intervals showing the Sun moving eastward away from Saturn. The sky is purposely left dark to show Saturn more easily.

   So with that in mind you could start watching for Saturn to reappear in the morning skies later next month.
   
   
   

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 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.

   
   
   
   

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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Sunspot on the Move

   The Sun is now displaying a rather large sunspot. It started appearing April 8th, and the following morning the sunspot was even more obvious. These pictures were taken with a Cannon Rebel EOS T7i with a Thousand Oaks Optical Solar Filter. This type of filter is a ‘visible light’ solar filter that makes it safe to look at, and take pictures of the Sun. In order to see flares, prominences and other features typically shown in solar images requires special filters. Among the more popular for ‘amateur use is a Hydrogen-alpha filter telescope.
    Camera settings for all pictures: 300 mm; f/32;/ ISO-6400; 1/60 sec .

   
   
   

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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Neptune and Vesta at Solar Conjunction

   Thursday March 7th the outer planet Neptune, and Asteroid Vesta reach a point in their respective orbit where they move behind the Sun as we view them from Earth. Neptune, or any of the other outer planets (Mars to Neptune), dwarf planets, or small solar system bodies beyond the Earth’s orbit, will all eventually reach this position on the opposite side of the Sun known as solar conjunction.
   For the two inner planets, Mercury and Venus, when they are at a similar position on the opposite side of the Sun, they are at superior conjunction.
   
   
   

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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Saturn at 2018 Solar Conjunction

10dec-saturn-solar-conjunction   Wednesday January 2nd the planet Saturn will have reached the astronomical coordinates that officially place it at solar conjunction. From our perspective the planet is behind the Sun, or on the opposite side of the Sun from the Earth.
   In reality it is not as much as Saturn moving behind the Sun as it is the Sun passing in front of Saturn – or so it seems. As a distant outer planet Saturn moves more slowly around the Sun than the Earth does. One year on Saturn is equal to 29.7 years (10,832 days) on Earth. So in one day Saturn would travel how much of the 360o orbit around the Sun? That would amount to approximately 0.033o each day.
   The Sun, in its apparent motion along the ecliptic moves at the rate the Earth is moving which is 0.99o each day. So with the Sun’s apparent motion (0.99o/day) it quickly, relative to Saturn, passes Saturn while both are moving eastward. So with that in mind you could start watching for Saturn to reappear in the morning skies later next month.

   
   
   

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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Mercury at Superior Conjunction

orbital-positions   Friday September 21st the innermost planet Mercury reaches superior conjunction. At superior conjunction Mercury will be on the opposite side of the Sun. The graphic to the right shows the planet positions relative to the Earth and Sun for both inner planets and outer planets.

   While at this superior 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 superior conjunction Mercury will be a few degrees north of the ecliptic and will cross the ecliptic moving south, descending node, on September 23rd.
   

   
   
   

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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