Mercury at Inferior Conjunction

orbital-positions   Wednesday December 13th 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). For this inferior conjunction Mercury will be north of the ecliptic.

   
   
   

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.

The Geminids-2017

   A few hours after sunset local time, on Wednesday December 13th, look toward the west for ‘shooting stars’, or meteors coming from the area around the constellation the Gemini Twins. These are the annual Geminid Meteor Shower – one of the best meteor showers each year, and at times rivaling the August Perseid Meteor Shower. The calculated peak time for the meteors is December 14th at 7 UT (2 am CST), but this does not mean that is the only time to view them. The Geminid Meteor Shower is named for the constellation that the meteors radiate outward from. This is the same for all meteor showers, and the ‘spot’ in the sky is known as the radiant. The Geminid radiant is just above the ‘twin’ star Castor, and under ideal viewing conditions an average of about 70 meteors per hour could possibly be seen. This year without the interference of moonlight will increase the chances of seeing the meteors.
   Meteor showers result from the Earth’s orbital path intersecting areas of comet debris. Comets, as they orbit the Sun, leave behind pieces of their icy, dirty, selves. If these debris clouds happen to be along the Earth’s orbital path then the Earth will regularly pass through the comet debris cloud. As this happens the small comet pieces hit our outer atmosphere and vaporize from the friction generated heat. We then see these as the shooting stars that make up meteor showers.
   There are, however, two exceptions to this. The January Quadrantid Meteors and the Geminids each come from their own respective asteroid rather than a comet. The source for the Geminids is Asteroid 3200 Phaethon

   
   
   
   

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

December Moon at Ascending Node

   Friday December 8th the waning gibbous Moon will be crossing the plane of the ecliptic moving north relative to the ecliptic. 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.


   On December 8th the 21-day old waning gibbous Moon will be within the boundaries of Leo the Lion and about 3o east from the ‘Heart’ of the Lion, the star Regulus.

   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)

Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”

   
   
   

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 at Perigee


   Our Moon reaches perigee, (closest distance from Earth), for this orbit on Monday November 4th. At that time the Moon will be at a distance of 28.025 Earth diameters (367,492 km or 222,135 miles) from the Earth. This is approximately 17 hours after full Moon making this full Moon the year’s Super Moon.
   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*


   On the day of the perigee Moon the 16.5-day old waning gibbous Moon is above the eastern horizon about 1 hour after sunset local time. The Moon is located just east of Orion’s club and Orion appears to be swinging his club as if it were a baseball bat toward the Moon – but missed. Strike One!!.

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

   Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”

   
   
   

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.

Neptune at Eastern Quadrature

1dec-neptune-east-quadrature   Sunday December 3rd the position of the planet Neptune with respect to the Earth and the Sun places this ringed planet at what is called Eastern Quadrature. Neptune is at a 90 degree angle from the Earth – think first quarter Moon as that is a fair comparison of the relative positions. At this position Neptune follows the Sun across the sky from east to west as the Earth is rotating, meaning that Neptune rises after the Sun and sets after the Sun.

   Where is Neptune now? The 8th planet from the Sun is currently within the constellation of Aquarius the Water Bearer and has recently completed its retrograde motion (November 22th).

   
   
   
   
   
   This is a 1 minute clip from a video I made showing Neptune and some of its moons as viewed from the Voyager 2 spacecraft. This clip is from a longer video of a tour of the solar system and was part of a live musical performance called “Orbit”. The performances were done at the Gottleib Planetarium in Science City at Union Station in Kansas City MO.

   

   
   
   

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.

Taurus Sniffs the Moon!

   Saturday evening November 2nd the 14.5-day old waxing gibbous Moon (full Moon tomorrow) will be a couple of degrees from the reddish star Aldebaran in Taurus the Bull. Aldebaran is at one end of a v-shaped open star cluster, the Hyades, that makes up the face of Taurus. Because of its reddish color it has been described as the angry eye of the bull.
   Normally the Hyades are a great view with binoculars as is the Pleiades, another open star cluster that is often described as a ‘baby dipper’.

   
   
   

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.

Mars – Spica Conjunction


   Starting with Wednesday November 27th and continuing for the next several days the ‘Red Planet’ Mars will pass within about 3-4o from the blue-white star Spica in Virgo the Harvest Maiden. This animated graphic is set for 5:30 am CST at 1-day intervals starting with November 27th and ending on December 3rd.
   Jupiter is several degrees further east from Mars but by this time of the morning Jupiter will have just risen.

   Those familiar with the starry sky probably have heard the mnemonic “Follow the Arc to Arcturus, then speed to Spica” as a way to use the stars forming the curved handle (the ‘Arc’) of the Big Dipper as a guide to the reddish star Arcturus and then Spica. Read a bit more about following the arc from a previous post.
   
   
   

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.