Sun Enters Capricornus not Aquarius- – 2019


 Monday January 20th at 9 UT the Sun in its apparent eastward motion along the ecliptic enters the boundaries of the constellation Capricornus the Sea Goat. This is the actual location of the Sun.
   Interestingly, according to the pseudoscience of astrology, 6 hours later, at 15 UT Monday January 20th, the Sun should be entering the constellation of Aquarius the Water Bearer.

   
   
   

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Mars on the Move

   Friday morning January 17th, before sunrise, the last quarter Moon will be about 5-6o from the blue-white star Spica in Virgo the Harvest Maiden. However the celestial highlight coming up is further east or lower and closer to the eastern horizon where there are two reddish-colored objects of about the same apparent brightness or magnitude. One object is the planet Mars and the other is the star Antares in Scorpius the Scorpion.

click on animated graphic to see it larger

Mars passing Antares – January 17-23 – 6 am CST

   Watch over the next several mornings and you will be able to determine which one is Mars and which is Antares as one of them moves past the other – as this animated graphic is showing. Also, relative to Mars and Antares the Moon is waning in phase as it zips past the two.

   There is an interesting connection between the star Antares and the planet Mars, based on their similar reddish color. There are times like this year when the two are close and part of the mythology surrounding the two suggests that the star was given its name so as to not confuse it with the planet Mars. The name Antares comes from the Greek word translated to ‘Rival of Mars’.

   Whenever that was historically Mars was probably known as one of the ‘wandering stars’ from the Greek word ‘planetai’. So with its reddish color, like blood, this ‘wandering star’ came to represent Mars, the ‘G-d of War’. Antares, on the other hand is a red supergiant star with a diameter estimated to be such that if it were at the center of our solar system Antares would fill the solar system out to around the main asteroid belt between Mars and Jupiter.

   
   
   

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Saturn at Solar Conjunction – 2019

   Monday January 13th 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 Earth 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. This animated graphic starts with Saturn and the Sun above the horizon a couple of hours after sunrise. The animation is set for 1-day intervals showing the Sun moving eastward away from Saturn. The sky is purposely left dark to show Saturn more easily.

   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.


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From a Crab to a Lion

   Over the next two evenings, January 11th and 12th, the waning gibbous Moon moves from near the Beehive Cluster, M-44, an open star cluster in Cancer the Crab to near the bright star Regulus in Leo the Lion. M-44, with an apparent magnitude of 3.50 in a dark sky without the Moon nearby is visible to the unaided eye and is easily seen with optical assistance like binoculars, or a low-power wide field eyepiece.


   
   
   

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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Waxing Gibbous Moon Near Aldebaran

   Tuesday evening January 7th the 13-day old waxing gibbous Moon will be about 3-4o from the reddish star Aldebaran. Aldebaran is known as the ‘angry’ red eye of the constellation pattern Taurus the Bull.

    Aldebaran is located at one end of a v-shaped cluster of stars making up the face of the Bull. This group of stars are all part of an open star cluster known as the Hyades. They are one of two naked-eye visible open star clusters within the boundaries of the constellation. The other one is the little dipper-shaped group known as the Pleiades.

   
   
   

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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Earth at Perihelion – 2020

   Feel the Heat?
   Sunday January 5th at 8 UT (3 am CST), as the Earth continues its annual trek around the Sun, the Earth reaches a point in its orbit that is called perihelion. Perihelion is the minimum distance that separates the Earth from the Sun, and we are the closest to the Sun for the year at this point in the orbit. So this year, 2020, the Earth is 0.9832 AU (91,398,199 miles : 147,091,144 km) from the Sun.

   Approximately one-half year or one-half revolution later, on July 4th, the Earth is at aphelion and is 1.01669 AU (94,507,634 miles; 152,096,155 km), its maximum distance from the Sun for 2020. This approximately 3% difference in distances between perihelion and aphelion is due to the shape of the Earth’s orbit being elliptical rather than circular. However the Earth has a mildly elliptically shaped orbit that is closer to being slightly out-of-round than the incorrect, very elliptical orbit that is often shown – like the illustration used here.

sun2014-ani   In Astronomy the shape of a planet’s orbit is called eccentricity, with 0 being a circle and 1 a straight line. Any value between 0 and 1 represents an ellipse. The shape of the Earth’s orbit is so close to being circular that the apparent size of the Sun does not appear to change as this animated graphic shows. The difference between perihelion and aphelion is about 3%.

   Eccentricity for each planet is listed below for comparison.

Planet	   Eccentricity	
Mercury	   0.2056
Venus	   0.0068
Earth	   0.0167
Mars	   0.0934
Jupiter	   0.0484
Saturn	   0.0542
Uranus	   0.0472
Neptune	   0.0086
Pluto	   0.2488

   To read more about the Earth’s orbit and get some teaching ideas click here to download a PDF copy of my January 2011 Scope on the Skies column Solar Explorations.
   Here is a good classroom activity about the Earth’s orbit and its effect on the apparent size of the Sun: Why Does the Size of the Sun Appear to Change? A Year of the Sun.


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Moon – Venus Conjunction

   Friday evening December 28th over the western horizon around sunset look for the 3-day old waxing crescent Moon to be about 2o from the inner planet Venus. Both will easily fit within the field of view of binoculars.

   I should clarify that the view of the conjunction as described above is based on my latitude and longitude in the midwest U.S.A. The separation between the Moon and Venus will vary depending on your location. At other geographic locations, like southern South America and Antarctica, the crescent Moon occults Venus.

   The occultation begins at 2 UT or for my time zone at 9:00 pm CST.

   This animated graphic is set for a latitude of 56oS to show the Venus Occultation. Venus was also enlarged to make it more visible in the graphic.

   
   
   

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