Jupiter at Eastern Quadrature

1apr-jupiter-east-quad   On Tuesday 1 April the position of the planet Jupiter with respect to the Earth and the Sun places the solar system’s largest planet at an orbital position called eastern quadrature. Jupiter is at a 90 degree angle from the Earth as this graphic shows. Think first quarter Moon as that is a fair comparison of the relative positions. At this position Jupiter follows the Sun across the sky from east to west as the Earth is rotating, meaning that Jupiter rises after the Sun and consequently sets after the Sun.
   Where is Jupiter now? Click here to see a graphic showing Jupiter and the star field of northern hemisphere winter and spring stars. I purposely chose a later time, 11:30 pm CDT, because at about that time Saturn and Mars will be visible above the eastern horizon.

   This is a short 6-7 minute video I made as part of a live musical performance called “Orbit” that was performed at the Gottleib Planetarium in Kansas City Missouri in May 2011. This is a piece from the much longer tour of the solar system performance and video and shows Jupiter, Saturn and some of their moons as viewed from the Cassini spacecraft.

   
   
   
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 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.

Heliocentric Opposition

   Today, Monday 11 November, Jupiter and Dwarf Planet Pluto will be at the position along their orbital path where they are on opposite sides of the Sun from each other. This is called a heliocentric opposition and is based on using the heliocentric coordinate system. This is essentially a horizontal system of 0-360 degrees as measured eastward around the Sun. Jupiter has a heliocentric longitude of 100 degrees compared with Pluto’s heliocentric longitude of 280 degrees. If nothing else what I think is interesting is how the orbits of these two planets compare with each other. The banner graphic at the top of the page shows the radius of each each planet. Pluto is 32.54 AU from the Sun, while Jupiter is only 5.17 Au from the Sun.

   
   
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.

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Jupiter in Retrograde Motion

Jupiter in Retrograde Motion

   Today at 7 UT (1 am CST) the outer planet Jupiter became stationary in its eastward orbital motion around the Sun. It will now begin moving backward toward the west. This reversal in motion is known as retrograde motion and is something that occurs to varying amounts as the Earth passes by each outer planet.
   The Earth passing by an outer planet is a result of the Earth having a faster orbital speed, and as the angles between Earth and an outer planet change there is the appearance of the outer planet slowing down and stopping its regular eastward motion. Then for a time ranging from a week or so to several months the outer planet appears to be moving backward or toward the west. After a time the planet resumes its eastward motion.
   Below is a short list with the Right Ascension (RA) and Declination (Dec) for Jupiter every 10 days showing the changing position of Jupiter during its period of retrograde motion. RA increases in value as a planet orbits toward the east and decreases in value during retrograde motion. Using the free equatorial star chart downloaded from the Stephen F. Austin Observatory the position of Jupiter could be plotted as the retrograde motion occurs. The last column shows the Jupiter to Earth distance in Astronomical Units (AU).

Date     RA       Dec     Distance
Nov  6  7 28   + 21 51   4.6996051
Nov 16  7 28   + 21 54   4.5643608
Nov 26  7 26   + 21 59   4.4447808
Dec  6  7 23   + 22 07   4.3456108
Dec 16  7 18   + 22 17   4.2713962
Dec 26  7 13   + 22 28   4.2255230
Jan  5  7 07   + 22 39   4.2104464
Jan 15  7 01   + 22 49   4.2271619
Jan 25  6 56   + 22 58   4.2748290
Feb  4  6 51   + 23 05   4.3514587
Feb 14  6 48   + 23 10   4.4536150
Feb 24  6 46   + 23 14   4.5769570
Mar  6  6 45   + 23 16   4.7169518
Mar 16  6 46   + 23 16   4.8685936
Mar 26  6 48   + 23 14   5.0271761
Apr  5  6 51   + 23 11   5.1884131

   
   
   
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.

Leaving Low-Earth Orbit – Finally?

Expanded View of New System

In what I think is the first step toward realizing the goal of taking crews beyond low-Earth orbit NASA has now approved plans that detail the design specifications and other features of a heavy lift vehicle capable of taking large payloads including crew beyond Earth orbit. This could mean crewed missions to the Moon, Mars, asteroids, and beyond(?).

Click here to read more about the Space Launch System (SLS)