Mercury at East Elongation

orbital-positions    On Sunday December 11th Mercury, the innermost planet, will reach its orbital position known as greatest eastern elongation. At that moment Mercury, the Sun, and the Earth, would be arranged in something close to approximating a right angle as this graphic shows.
   From our perspective the orbits of Mercury and Venus appear to move from one side of the Sun to the other – out to the left (east) from the Sun to eastern elongation, then reverse and move westward (inferior conjunction) between the Earth and the Sun to western elongation.
click on animated graphic to see it larger    From there the inner planet moves eastward going behind the Sun (superior conjunction) and eventually reappearing on the eastern side of the Sun for an eastern elongation. Repeat over and over – do not stop!
   This animated graphic shows Mercury at its eastern elongation and its orbital path. The horizon is removed in one graphic so Mercury’s orbit around the Sun could be visualized better.

   
   
   
   

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.

Saturn at Solar Conjunction: 2016

10dec-saturn-solar-conjunction   Saturday December 10th the planet Saturn will have reached the astronomical coordinates that officially place it at solar conjunction. From our perspective the planet is behind the Sun, or on the opposite side of the Sun from the Earth.
   In reality it is not as much as Saturn moving behind the Sun as it is the Sun passing in front of Saturn – or so it seems. As a distant outer planet Saturn moves more slowly around the Sun than the Earth does. One year on Saturn is equal to 29.7 years (10,832 days) on Earth. So in one day Saturn would travel how much of the 360o orbit around the Sun? That would amount to approximately 0.033o each day.
   The Sun, in its apparent motion along the ecliptic moves at the rate the Earth is moving which is 0.99o each day. So with the Sun’s apparent motion (0.99o/day) it quickly, relative to Saturn, passes Saturn while both are moving eastward. So with that in mind you could start watching for Saturn to reappear in the morning skies later next month.

   
   
   

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.

A Planet Buffet

   Friday night December 9th offers up a planet buffet featuring eight planets above the horizon and one under your feet. As this graphic shows one of the outermost of the 8 planets, Uranus, is above the eastern horizon as are two Dwarf Planets, Ceres and Eris, and the waxing gibbous Moon. Further west over the southern horizon is the outermost of the 8 planets, Neptune, and over the southwest horizon are Mars, Venus, Pluto, and Mercury. And under your feet? Look down to see the Earth – can’t miss it!
   Ceres is the closest Dwarf Planet to us as it is within the main asteroid belt between Jupiter and Mars. The other Dwarf Planet is Eris which at 96 AU is located much further than Ceres (2.2 AU) and Uranus (19.4 AU) and Neptune (30 AU).

   
   
   

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.

Follow the Arc to Spica, or Jupiter

   There is an ‘old’ Astronomical saying, a sort of memory aid, for finding at least two constellations by way of their alpha, or brightest star in their respective constellation. In Bootes the Herdsman there is the orange-reddish star Arcturus, and in Virgo the Harvest Maiden the bluish-white star Spica. The saying – “follow the arc to Arcturus, then speed to Spica” is how you connect these two stars with the curve, or arc, in the handle of the Big Dipper. This is typically done during the Northern Hemisphere spring and summer season when Bootes and Virgo are in the evening skies. However during the late autumn and winter months in the Northern Hemisphere this memory aid works best in the early morning skies before the Sun rises.
   So despite the graphic showing the morning sky for December 8th you could go out any morning for the next few months and find the 7 stars making up the Big Dipper. Then look for the curved handle and follow the arc or curved handle toward Arcturus and then continue on to Spica, or for the time being, the planet Jupiter.

   
   
   

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.

December Moon Descends on Neptune

   Well not exactly descending on Neptune but on Tuesday December 6th the first quarter Moon will be crossing the plane of the ecliptic moving south. This is known as the descending node, one of two intersections the Moon’s orbital path (dark green line) has with the ecliptic. Several hours after the node crossing the Moon will pass within less than 0.5o from Neptune – that separation depending on your longitude/time zone.
(The Moon and Neptune in the graphic have exaggerated sizes.)
   

   On the day of the node crossing the 7-day old first quarter Moon rises around mid-day local time and is visible most of the night, setting a couple of hours after midnight.

   
   
   

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.

Moon Passes Mars

   The waxing crescent Moon will pass by the red planet Mars on December 4th and 5th as this animated graphic below is showing. The graphic is set for around 7 pm CST.

   
   
   

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.

ISS This Evening

   This evening, Thursday December 1st, the International Space Station, ISS, did another orbit over my part of the world as it first appeared in the southwest near the setting waxing crescent Moon. It climbed to nearly straight overhead as it passed by the stars of Delphinus the Dolphin, Sagitta the Arrow, and Deneb in the Cygnus the Swan, until it passed out of my camera’s field of view. I continued to watch it cruise past the stars of Cassiopeia the Queen high over the northeast horizon.

   This was my first time for seeing the entire flyover from when the ISS appeared in the southwest until it faded out near Cassiopeia. Pretty cool.
   Camera settings: 21 stacked pictures at 18mm; ISO 1600; f3.5; 3.5 sec; at 2 second intervals.
   

   
   
   

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.