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.
   
   
   
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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.

Mars Watch

mars-spica-ani   The planet Mars rises a couple of hours before the Sun rises and is easily seen just a few degrees above the bluish-white star Spica in the constellation Virgo the Maiden. Mars is currently moving eastward and during this month it will stay close enough to Spica that the two will fit within the field of view of 7×50 binoculars as this animated graphic shows. Each frame of the graphic shows the daily position of Mars relative to Spica for February. On the 19th the waning gibbous Moon is very close to Spica.
   Click here to see a graphic showing the pre-dawn sky with Mars, Spica, Saturn, and Antares.

   
   
   
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 Watch

Mercury 1 to 13 February 6 pm CST

Mercury 1 to 13 February 6 pm CST

   This evening and for the next several the innermost planet Mercury will be visible at sunset above the southwest horizon as the banner graphic at the top of the page shows. Mercury reaches inferior conjunction, between the Sun and Earth, on the 15th and between now and then Mercury will be moving west toward the Sun. Each evening at the same time Mercury may be observed to be lower above the horizon as it moves toward inferior conjunction as this animated graphic is showing.
You might also notice that in each frame (day) the Sun is a little higher at the same time. This is the Sun’s apparent daily eastward motion along the ecliptic. This is also why it takes such a relatively short time for Mercury to orbit from eastern elongation to inferior conjunction. Combine the Sun’s nearly 1 degree/day east with Mercury’s westward orbital motion of 4 degrees/day and it is easy to see why the ‘closing rate’ is so fast.
mercury-phases-ani     Another interesting and observable change is Mercury waning from a small gibbous phase to a larger crescent phase as this small animated graphic is showing. It shows the planet from the 1st to the 15th when Mercury reaches inferior 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.