Mercury in Motion

mercury-ani
   This week my students worked on a lab involving the planet Mercury. Part of the lab was to determine the dates for the next elongations of Mercury and also the degrees of elongation. As they worked on their lab they were able to observe Mercury (using software) as it moved from eastern elongation last month through inferior conjunction and then to western elongation next month. I was so pleased when some of them commented that Mercury was moving in retrograde motion as it traveled through inferior conjunction, October 16th, as the animated graphic is showing.
   In the animated graphic I have added the ecliptic (green line) to show the relationship between Mercury’s orbit and the ecliptic. Mercury is inclined 7o from the plane of the ecliptic and as you can see it is below the ecliptic, with the 4th of October as its maximum separation from the ecliptic.

Click on graphic to see it full size.

Click on graphic to see it full size.

   Currently Mercury is still setting after the Sun sets but that will not be for much longer. As the students noticed, when you combine Mercury’s orbital speed (which right now is toward the west and the Sun) with the apparent motion of the Sun toward the east the two close in on each other rather quickly – at least compared to when Mercury is moving toward the east after western elongation. Mercury moves at approximately 4o per day compared with the Sun’s apparent motion of approximately 1o per day.
   
   
   
[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.

Mercury at Superior Conjunction

mercury-ani   Today or late last night depending on your time zone at 6 UT (Midnight CST) the innermost planet Mercury reached what is called superior conjunction. at this position the planet Mercury is on the opposite side of the Sun from the Earth. From superior conjunction the planet Mercury will continue moving eastward and will become visible as an evening planet during January.

   
   
   
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.

The Elongated Mercury

   This evening the waxing crescent Moon and three planets will be above the western horizon at sunset, however depending on your latitude and shape of your local horizon Mercury and Saturn may be a challenge to see. Adding to that is at the time of sunset the sky is still too bright to see these planets with the naked eye. And by the time the sky darkens enough, maybe another 20 minutes or so, Mercury and Saturn may have already set.

Mercury at Elongation

9 October: Mercury at Greatest Eastern Elongation

   The Planet Mercury has reached the point in its orbit around the Sun where it is at its maximum angle out from the Sun as we see the two of them from here on Earth. This is known as an elongation. Since Mercury is currently on the left or east side of the Sun it is an ‘evening planet’ setting after the Sun, and today it is at its Greatest Eastern Elongation.
   Not one to stop, Mercury continues moving until reaching greatest western elongation at the end of next month. Until then the innermost planet will be moving in retrograde or toward the west. As Mercury moves west at the rate of about 4 degrees each day the Sun in its apparent motion toward the east is moving about 1 degree each day. So in less than a month, on 1 November, Mercury will have reached inferior conjunction, between the Sun and Earth.

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