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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Mercury at Inferior Conjunction

orbital-positions   Saturday August 26th the innermost planet Mercury reaches inferior conjunction. At inferior conjunction Mercury will move between the Earth and the Sun – much like the position of the Moon at new phase. 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 inferior 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).

   
   
   

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.

Mercury at Inferior Conjunction

orbital-positions   Thursday 19 June at 23 UT (6 pm CDT) the innermost planet Mercury reaches inferior conjunction. As the banner graphic at the top of the page shows, inferior conjunction of Mercury places Mercury between the Earth and the Sun – much like the position of the Moon at new phase. The graphic to the right shows the relative to the Earth and Sun position names for both inner planets and outer planets.

   The short video below, taken by the Mars Curiosity Rover, shows a transit of the Sun by Mercury as seen from the surface of Mars.

   
   
   
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.

A Lunar Twin?

Click on graphic to see it full size.

Click on graphic to see it full size.

   Friday evening, 30 May, the thin 2 day old waxing crescent Moon will be within about 6-7 degrees from the inner planet Mercury. And both will display a crescent phase shape due to their respective position to the east from the Sun, as the banner graphic at the the top of the page shows. However the Moon is in its waxing phases having just been at new Moon and now moving eastward from the Sun. While Mercury is in its waning phases as it is moving in retrograde, to the west, toward the Sun and inferior conjunction next month.

   
   
   
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.

Venus at Western Elongation

inner-planets-positions   Today Venus reaches the point in its orbit called greatest western elongation. As this graphic shows the inner planet Venus, or Mercury, is more or less at a right angle (90o) from the Sun and Earth at western elongation. From the surface of the Earth, your backyard, for example, Venus is to the right, or western side of the Sun and is rising before the Sun.

Click on graphic to see it full size.

Click on graphic to see it full size.

   At western elongation Venus, or for that matter Mercury the other inner planet, is as far out from the Sun as we see them and as a result Venus or Mercury will rise at the latest time in this orbit. Today Venus will be 46.6o from the Sun. From western elongation forward Venus or Mercury will be moving eastward toward the Sun and each day rising closer and closer to the time of sunrise. As the planet moves eastward it is moving further away from the Earth toward superior conjunction on the opposite side of the Sun. As the distance between the Earth and Venus, or Mercury, increases combined with the decreasing angle between the planet, the Earth, and the Sun, Venus or Mercury decreases in apparent size and also waxes through gibbous phase shapes but we never see it at a full phase since that is at superior conjunction.

   
   
   
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.

Mercury at Inferior Conjunction

orbits   From our perspective on Earth, the inner planet Mercury appears to move back and forth from the left side of the Sun to the right side and then back to the left side – over and over. This is our view of the planet as Mercury revolves around the Sun. From an overhead view we would see Mercury’s orbit circular as shown in the graphic to the right. However since the Earth’s orbit is essentially on the same plane, or level, as Mercury’s orbit we see Mercury move from one side of the Sun to the other side. Sort of back and forth motion from the east to the west side of the Sun with Mercury, today, centered between the two extremes (elongations) and at inferior conjunction.

From this Inferior Conjunction to the next one.

From this Inferior Conjunction to the next one.

   Mercury’s orbit is divided into four parts based on the planets position (location) relative to the Earth and the Sun somewhat like we describe phases of our Moon. Starting with today Mercury is between the Earth and the Sun at inferior conjunction. In approximately 1/4th of a revolution Mercury will be to the right of the Sun at western elongation – when Mercury rises before sunrise, and is known as a ‘morning star’. One-fourth of a revolution later Mercury is on the opposite side of the Sun, not visible from the Earth, and is at superior conjunction. Continuing along its orbital path Mercury will reach eastern elongation, on the left side of the Sun when it will rise after the Sun rises and sets after the Sun, as an ‘evening star’.
mercury-phases-ani   Viewing Mercury through a telescope will reveal phase changes similar to our Moon with the biggest difference being that there is no full Mercury phase—at least not one that we can see from Earth. Today while at inferior conjunction the Sun side of Mercury is reflecting sunlight and so like our new Moon phase we do not see either. Mercury moves from inferior conjunction toward western elongation and as it does so it starts as a relatively large crescent phase and by western elongation Mercury’s apparent size has decreased but it has waxed toward a quarter phase and 50% illuminated. As Mercury moves toward superior conjunction its apparent size decreases while its phase waxes through the gibbous shape. Once the planet moves away from the Sun and superior conjunction Mercury will be again seen in the gibbous phase but appears relatively small. As it continues along its orbit toward eastern elongation Mercury wanes to a larger appearing quarter phase and 50% illuminated. From eastern elongation to inferior conjunction Mercury’s apparent size increases while it wanes toward a thin crescent shape.
On March 14th Mercury reaches western elongation.

   
   
   
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.