Sun Enters Cancer

19july-view-from-earth   Thursday July 20th the Sun in its apparent eastward motion along the ecliptic, moves out of the constellation Gemini the Twins and into the constellation of Cancer the Crab. This is the true or actual position of the Sun as opposed to the pseudoscience of astrology which usually has the astrological Sun one constellation ahead or east from the Astronomical Sun’s position.

   Read a little more about how astrology has the Sun incorrectly placed in a previous blog, and in another blog discussing the effects of precession.
   
   
   

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.

Mars and Neptune Conjunction, inlcuding the Moon and Venus


   A previous post described the daily motion of Mars as it moves toward the planet Neptune. Well Monday evening January 2nd the planets Mars and Neptune, and our Moon (a 5-day old waxing crescent Moon) will all fit within the field of view of binoculars with Mars and Neptune separated by about 1.5o.

   In that post I had also mentioned that were Neptune observed from the surface of Mars then Neptune would be starting its retrograde motion. Actually I was not entirely correct as I was basing this on how the two planets looked from Earth rather than Neptune as seen from Mars. Compare the distance between the Earth and Mars and the difference between the orbital speed of the two planets. Then consider Mars and Neptune where there is a greater difference between the orbital speeds of Mars and Neptune as well as the distance between the Mars and Neptune then there is between the Earth and Mars.

   What this means is that Neptune, as viewed from Mars, will not actually begin to retrograde until around the middle of June.

   
   
   

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.

October Moon at Perigee

16oct-perigee_moon   The Moon reaches perigee, (minimum distance from Earth), this month on Sunday October 16th. At that time the Moon will more or less be at a distance of 28.05 Earth diameters (357,861 km or 222,364 miles) from the Earth.
   The Moon reaches perigee Sunday at 23:47 UT (6:47 pm CDT) and this is less than 20 hours after it was at full Moon phase also on Sunday but at 4:23 UT, (11:23 pm CDT October 15th). Since the full Moon is this close to its closest to the Earth for this orbit the full Moon could be considered one of the ‘Super Moons’ this year.
   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 lunar perigee the 16-day old just past full waning gibbous Moon rises at around sunset local time and is over the southwest horizon at sunrise the following morning. Two of the Dwarf planets, Eris and Ceres are near the Moon but due to their respective apparent magnitudes (Ceres 7.0; Eris 18.6) and the bright reflected light from the Moon the two are all but invisible. Interestingly these two represent two similar but very different types of Dwarf Planets – Ceres is within the main asteroid belt at a distance of 1.9 AU (176,616,033 miles; 284,235,954 km) while Eris is in the outer regions of the solar system at a distance of 95 AU (8,830,801,690 miles; 14,211,797,715 km) from 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 go to bobs-spaces.

September Moon at Ascending Node #2

1sep-ascending-node   Wednesday September 28th the waning crescent 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 the morning of the 28ththe Moon will rise as a very thin 27-day old waning crescent Moon.

   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.

Moon Passes the Hyades

   Over the next couple of nights or early mornings the waning gibbous Moon will pass across the stars of the Hyades, a v-shaped open star cluster that makes up the face of Taurus the Bull. Depending on your geographical location you may see the Moon either pass very closely to the reddish star Aldebaran.
    From parts of Eastern Africa, Middle East, and South Asia the waning Gibbous Moon will be within 0.2o from Aldebaran.
   
   
   

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.

Mercury at Inferior Conjunction

orbital-positions   Monday September 12th 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.

mercury at inferior conjunction   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). In this situation Mercury is still south of the ecliptic but heading toward its ascending node on September 23rd.

   
   
   

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.

Mercury Begins to Retrograde

mercury-retrograde-ani   The innermost planet Mercury is about 2 weeks after its Greatest Eastern Elongation on August 16th. As the name suggests Mercury has been on the east (left) side of the Sun and visible in the evening skies after sunset. From a combination of the Earth’s and Mercury’s orbital speed and angle relative to each other Mercury is now seen as moving westward toward Inferior Conjunction on September 12th. Mercury will continue moving westward until it reaches its Greatest Western Elongation on September 28th.
   Retrograde or westward motion is probably best known as it relates to the apparent motion an outer planet relative to the Earth has. mars-retrograde-aniThis apparent westward motion comes about as the Earth, moving faster than an outer planet, catches up with and passes the slower moving outer planet. As this happens the outer planet appears to slow down, pause, then move westward for a period of time lasting from days to weeks. At some point the angle between the Earth and the outer planet has shifted enough so that it appears as if the westward motion has ended and the outer planet resumes its direct or eastward motion around the Sun.
   For an outer planet this is an apparent motion relative to the stars in the background, while for the two inner planets they really do move westward as they orbit the Sun between eastern and western elongation, and along the way passing between the Earth and the Sun at inferior conjunction.

   
   
   

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.