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.

Along the Ecliptic

   In the posting yesterday I described the shape, or eccentricity, or the Earth’s orbit as not being a factor in how we have seasons. As we all should have learned it is the tilt of the Earth’s rotational axis relative to the plane of the ecliptic. This tilt is approximately 23.5o and this combined with revolution around the Sun is as they say ‘the reasons for seasons.’
    But this is not the point of this posting, but rather it is the plane of the ecliptic and where planets, dwarf planets, and our Moon orbit relative to the plane of the ecliptic. This relationship is known as inclination and it is the angle, in degrees, above the plane of the ecliptic. What this means is that the Earth’s orbit the bright green line, which is in reality the ecliptic, is the reference plane from which the other Sun orbiting objects respective orbit is tilted from. If you follow this explanation, and perhaps have read or noticed that each month I have posted when the Moon reaches its ascending or descending node. This ascending and descending node also applies to the other planets and dwarf planets as well because the planets and dwarf planets, like our Moon, have orbital paths tilted away from the plane of the ecliptic as this graphic shows. The table below shows the inclination for the planets and one dwarf planet.

   What got me started on this was in part from what I wrote yesterday but also yesterday evening as I was attempting to get some pictures of the rising full Moon through some trees. This was despite the air temperature being near 0° F! Nonetheless as I was looking around enjoying the first really clear sky evening in a several weeks I couldn’t help but notice how Mercury, Venus and Mars were lined up from west to east along where I visualized in my mind the location of the ecliptic. Then using my ‘go to’ Astronomy simulator I set up a slideshow with the ecliptic, planets, a few dwarf planets, and our Moon displayed and set to 1-hour intervals starting with sunrise 7:30 am CST, my local time. You can see how the planets are very close to the ecliptic compared with the dwarf planets. The Moon is sometimes below, sometimes above, and sometimes right on the ecliptic – which if timed right gives us an eclipse.

Inclinations of 8 Planets and 1 Dwarf Planet
Name	Inclination
Mercury	7.01°
Venus	3.39°
Earth	0°	
Mars	1.85°	
Jupiter	1.31°
Saturn	2.49°
Uranus	0.77°
Neptune	1.77°
Pluto	17.15°

This slideshow requires JavaScript.

   
   
   
[centup]
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 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.
   
   
   
[centup]
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.

Here Come the Orinids

Sunday 21 October – 4 am CDT

   The Orionid Meteor shower reaches its peak on the morning of Sunday the 21st. Best viewing is looking toward the east to south part of the sky after midnight and before sunrise. Look for the stars of Orion – most find Orion from the 3 bright stars forming his belt. Look to the left from the belt stars for the bright reddish-orange star Betelgeuse (often pronounced ‘beetle juice’) that represents Orion’s right shoulder. A little further to the left from Betelgeuse is the radiant, the area where the meteors or shooting stars will seem to be radiating outward from.
   All annular meteor showers, like Orionids, and the more well-known August Perseids, are named for the constellation the radiant is located within. Meteor showers are the result of several factors including the reaction between the comet’s dirty, icy surface with the Sun’s radiant energy and the orbital path the Earth and comets follow around the Sun. All comets leave behind clumps or clouds of comet debris, their surface material, as they come closer to the Sun’s heat energy. Some of this comet debris is left along the Earth’s orbital path such that the Earth regularly passes through these debris clouds. As the Earth passes through the debris the small bits of rock enter the Earth’s atmosphere and as they heat from friction and melt they glow briefly appearing as streaks of light. Some meteors leave a bright glowing trail, called a train, for a few moments. The Orionids average around 20 meteors per hour, however this year estimates are that that number may go up to as many as 60 per hour.
   How the number per hour can increase is based on the debris cloud and where the Earth passes through it. The debris is cloud-like in its shape and there are parts of the ‘cloud’ where the particles are more numerous – the thicker parts of the debris cloud. Meteor showers, like the Earth’s orbit are pretty well known so part of the equation for determining the number per hour is based on knowing what part of the debris cloud the Earth will pass through. This year we apparently pass through a thicker part of the debris cloud.
   Hang on to your hat!

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