Moon on the Move

   Over the next few evenings, Saturday December 14th, Sunday the 15th, and Monday the 16th the waning gibbous Moon will orbit eastward starting from about 7-8o south of Pollux to passing about 6-8o from M-44, the ‘Beehive Cluster’, an open star cluster in the constellation Cancer the Crab. By Monday the 16th the waning gibbous Moon will be about 2o from the heart of Leo the Lion, the star Regulus.
   During a 24-hour rotation of the Earth the Moon will have moved approximately 15o eastward. In terms of Moon position that 15o is equal to one hour — (divide 360o by 24 hours = 15o). What this has to do with the Moon’s position is that each day or night the Moon rises about 1 hour earlier. These 3 graphics show the effect of this in that it will be about 1 hour later for the Moon to be more or less in the same spot in the sky relative to the horizon.

   
   
   

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December Moon at Ascending Node

   Friday December 13th the 17.5-day old waning gibbous Moon rises between the legs of the Gemini Twins. The Moon will be about 10-11o to the west from the ‘Twin’ Stars Pollux and Gemini. As it is rising the Moon will be crossing the plane of the ecliptic moving north. This is known as the ascending node, one of two intersections the Moon’s orbital path has with the ecliptic. The ecliptic is actually the Earth’s orbit and the Moon’s orbit is inclined about 6o from the ecliptic. So there are two node intersections, the ascending and descending nodes.

   Does our Moon actually go around the Earth as many graphics show? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*
*Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

   

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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Venus – Saturn Conjunction

   Wednesday evening November 11th look toward the western horizon for a grouping of 3 planets and one dwarf planet. Very low over the horizon and possibly to low to be seen is the outer planet Jupiter. About 7-8o east from Jupiter is the dwarf planet Ceres, however at nearly 9th magnitude and low above the horizon Ceres will be difficult to see, if at all.
   Several degrees east from Jupiter and Ceres is the brightly shining inner planet Venus and about 1-2o from Venus is the outer planet Saturn. These two planets will make a nice contrast in apparent magnitude (Venus: -3.95 Saturn: 0.57) as they easily will fit within the field of view of binoculars.

   
   
   

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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Moon Conjunction with Aldebaran

   Tuesday evening, November 10th, about an hour or so after sunset, the 14.5-day old waxing gibbous Moon will be about 2-3o from the reddish star Aldebaran. Aldebaran is at one end of the v-shaped open star cluster the Hyades in Taurus the Bull.

   
   
   

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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A Couple of Morning Planets

   Early chilly mornings yes, but two planets are visible before the Sun rises. Maybe seeing Mars and Mercury will make it worthwhile? They are both within the realm of the constellation Libra the Scales. As a bonus Dwarf Planet Haumea is also above the horizon but with an apparent magnitude of 17.0 it is virtually invisible without some optical assistance.

   
   
   

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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December Moon at Apogee

   Our Moon reaches apogee, (greatest distance from Earth), for this orbit, on Thursday December 5th. At that time the Moon will be at a distance of 31.70 Earth diameters 251,311 miles (404,447 km) from the Earth.

   On the day of the apogee Moon the 9-day old waxing gibbous Moon rises during mid-afternoon and sets later the following morning several hours before sunrise..

   Does our Moon actually go around the Earth as this graphic shows? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*

   *Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.


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Tales Along the Ecliptic

   Once in a while the planets are arranged such that they are spread across the sky as they look in this graphic. However over time, several days, this arrangement changes as the planets continue moving along their orbits.
   The planets are not lined up in a straight line outward from the Sun but rather are arranged along the ecliptic. The ecliptic is the Earth’s orbital path around the Sun and the respective orbit of each planet is inclined from the ecliptic. And this is one of those times when it is easy to visualize the ecliptic. Click here to read a previous posting about the ecliptic and planet inclination.

   This animated graphic is showing the terrestrial planets as they move along their respective orbits for this month. They are not ‘lined up’ as they appear to be in the above horizon picture.

   This graphic shows the solar system out to Neptune and from this perspective the planets are obviously not in a straight line on December 1st.

   
   
   

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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