Earth at 2017 Aphelion

Earth at Perihelion   Monday July 3rd, 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 20 UT (3 pm CDT) on Monday July 3rd the Earth is 1.01668 AU (94,506,310 miles; 152,093,163 km) from the Sun.
   Approximately one-half year or one-half revolution earlier, on January 4th, the Earth was at perihelion, its minimum distance from the Sun for this year (0.98331 AU (91,404,375 miles; 147,101,082 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 go to bobs-spaces.

Mercury at Aphelion

mercury at aphelion   Sunday February 21st the innermost planet Mercury reaches aphelion, its furthest distance from the Sun, 0.4667 AU, (69,817,326 km; 43,382,475 miles). Interestingly, I suppose, is that the next time Mercury reaches aphelion will be May 19th, 10 days after the Mercury transit of the Sun.

   All planets orbit the Sun with an orbital shape that is not circular but rather elliptical. How much away from being a circle is called eccentricity of an orbit. With 0 representing a circle and 1 a straight line Mercury, with an eccentricity of 0.2056, has the greatest eccentricity of the other 7 planets. The dwarf planet Pluto, for comparison, has an eccentricity of 0.2488.

   
   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Earth at Perihelion 2015

jul6-earth-aphelion   Monday 6 July, 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 20 UT on Monday 6 July (3 pm CDT) the Earth is 1.01668 AU (94,506,310 miles; 152,093,163 km) from the Sun. Approximately one-half year or one-half revolution later, on January 2nd, the Earth is at perihelion and is 0.98330 AU (91,403,445 miles; 147,099,586 km), its minimum distance from the Sun for the year. This 3% difference 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 more observing information.

Earth at its 2015 Perihelion

Earth at Perihelion   Feel the Heat?
   Sunday January 4th at 7 UT (1 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, at 12:00 UT (0600 CST) the Earth is 0.98328 AU (91,401,586 miles; 147,096,594 km) from the Sun. Approximately one-half year or one-half revolution later, on 6 July, the Earth is at aphelion and is 1.01668 AU(94,506,310 miles; 152,093,163 km), its maximum distance from the Sun for 2015. This difference 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.
   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.
   
   
   
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Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Earth At 2014 Aphelion

Earth at Perihelion   Friday 4 July, 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 0 UT on Friday 4 July (7 pm CDT Thursday 3 July) the Earth is 1.01682 AU (94,519,324 miles; 152,114,107 km) from the Sun. Approximately one-half year or one-half revolution later, on 4 January, the Earth is at perihelion and is 0.98330 AU (91,403,445 miles; 147,099,586 km), its minimum distance from the Sun for the year. This difference 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 more observing information.

Earth at 2014 Perihelion

Earth at Perihelion   Today, Saturday 4 January 2014, 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, at 12:00 UT (0600 CST) the Earth is 0.98330 AU (91,403,445 miles; 147,099,586 km) from the Sun. Approximately one-half year or one-half revolution later, on 4 July, the Earth is at aphelion and is 1.01682 AU(94,519,324 miles; 152,114,107 km), its maximum distance from the Sun for 2014. This difference 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 more observing information.

So Close, Yet So Cold!

not drawn to scale

not drawn full size

   Today, Tuesday 1 January 2013, 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, at 11 p.m. CST (0500 UT 2 January) the Earth is 147,098,161 km from the Sun. Approximately one-half year or one-half revolution later, on 5 July, the Earth is at aphelion (152,097,427 km), its maximum distance from the Sun for 2013. This difference 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.
   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.

   Caveat: “The above comments are obviously northern hemisphere biased, and I make no apologies to those in the opposite hemisphere who may be sitting on a beach somewhere enjoying strawberries and cream.” He said with a big grin.
   
   
Click here to go to the Qué tal in the Current Skies web site for more observing information.

Feed Me!

Devouring a Planet

   “Fried Planets” is the title for a recent News Release from NASA describing observations and data collected from a star in the constellation of Perseus the Hero. Using a 9.2 m telescope at the McDonald Observatory in the Davis Mountains of West Texas the star, BD+48 740 – a red giant star, has apparently destroyed, “devoured” one of its planets. This conclusion was reached after spectroscopic studies of the star revealed an abundance of the element Lithium in the red giant star. Lithium is typically destroyed during nuclear reactions in a star, so finding it in the amounts they detected suggests that this extra Lithium came from a planet or planets orbiting the red giant star. These planet or planets were close enough to the star to be engulfed and destroyed by the star as it expanded into a red giant star.
   Additionally the one planet still in orbit around BD+48 740 has an orbit that is the most elliptically shaped orbit for any planet observed so far – in our solar system or any of the exo-solar systems. The planet, roughly 1-2 times the mass of Jupiter, may have moved into this elliptical orbit during the time the planet or planets providing the Lithium were being destroyed by the red giant star.

Watch a ScienceCast video from NASA about this star and its activities.

Click here to go to the Qué tal in the Current Skies web site for more observing information.