Week of December 16, 2013

This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Monday, December 16.  All times are given as local St. Louis time (Central Standard Time).  For definitions of terminology used in the night sky update, click the highlighted text.

Information updated weekly or as needed.

Join us for our next star party, Friday, January 3, 2014 held in association with the St. Louis Astronomical Society. For details, see the information at the bottom of this page.

The Sun and the Moon

Sunrise is at 7:12 a.m. on Monday, December 16 and sunset is at 4:41 p.m. providing us with less than 10 hours of daylight.  Even after sunset, the light from the Sun will still illuminate our sky for about one hour and 30 minutes.  This period of time is called twilight, which ends around 6:16 p.m. this week.  For those with a sun dial, solar transit or local noon occurs around 11:57 a.m. this week.  We are entering our last few days of fall as the Winter Solstice occurs this week on December 21.  On January 4, 2014 Earth will be at it closest to the Sun.  This fact may sound strange as temperatures are lower in the winter.  Proximity to the Sun is not what drives the Earth’s seasonal temperature changes but rather the Earth’s axial tilt.  Due to the Earth’s rotational axis being tilted 23.4 degrees the northern and southern hemispheres will spend part of the year pointed away from or towards the Sun.  During these periods one hemisphere receives less or more direct sunlight which in turn drives the changes in temperature.  If you would like more information on Earth’s seasonal change visit


Moonrise for Monday, December 16 occurs at 4:31 p.m.  Moonset will occur at 7:10 a.m. on the following day.  Full moon occurs on December 17.  December’s full moon is named the Full Cold Moon.  

International Space Station (ISS) Observing

The next visible passes of ISS over St. Louis are all evening passes.  None of the passes listed below are great due to the low altitude of each pass.  The two best passes are on the evenings of December 17 and 23.  Learn more about the passes and others this week in the table below.

Catch ISS flying over St. Louis in the evening hours starting Monday, December 16. 





Max. altitude











16 Dec











17 Dec











22 Dec











23 Dec











23 Dec












Magnitude (Mag): The Measure of brightness for a celestial object.  The lower the value is, the brighter the object will be.

Altitude (Alt):  The angle of a celestial object measured upwards from the observer’s horizon.

Azimuth (Az):  The direction of a celestial object, measured clockwise from an observer’s location with north being 0°, east being 90°, south being 180° and west being 270°.

For information about ISS flyovers and other visible satellites, visit www.heavens-above.com

Detailed information regarding all unmanned exploration of our universe, missions past, present, and planned, can be found at Jet Propulsion Laboratories:


The Planets Visible Without A Telescope


The brightest planet in the sky is well into another evening apparition becoming visible about 20 minutes after sunset.  Venus will be low to the horizon and any trees or buildings southwest of you may obscure it from view.  Venus is currently seen in the constellation Sagittarius and will set by 7:07 p.m.  If you have binoculars at home you should notice that Venus in a crescent phase.  Due to Venus being closer to the Sun it is always in a phase similar to those we see the Moon exhibit.  The difference is Venus is always closer to the Sun so we never see a full Venus.  As Venus approaches its inferior conjunction in January next year, Venus will exhibit a thinner and thinner crescent shape.    


Mars is now in the constellation Virgo and will rise around 12:38 a.m. this week.  For those awake around 2:00 a.m. look to the east and you will see a reddish-orange object just above the horizon.  Mars will be seen earlier each week as we start to catch up with it in our orbit.  Mars will be close to us again in 2014 reaching opposition on April 8, 2014.  Fans of Mars rejoice it is back and on its way to another close approach.


The largest planet in our solar system has returned to our evening skies.  This week it will rise around 6:18 p.m. becoming visible roughly 30 minutes later.  Just above and to the east of Jupiter you will see the 1st magnitude stars Castor and Pollux.  Looking at these stars and then comparing them to Jupiter you will see that the stars are twinkling and Jupiter is not.  The twinkling you see is called scintillation which is a distortion of the stars light by Earth’s atmosphere.  Testing for scintillation is how you can distinguish stars from planets. 


Saturn is climbing out of the glare of the Sun by 4:17 a.m.  Morning twilight will still be a small problem and trees and buildings will continue to obscure our views.  For those that can find a clear eastern horizon you should be able to spot Saturn by about 5:15 a.m.  Binoculars will help but as the month goes Saturn will become easier to see.

Constellation of the Month

Each month we will highlight one constellation and some of the objects that can be found within the boundaries of that constellation.  At the start of the month we will list only a few of these objects and each week we will add another to the list.  Some objects will be visible to the unaided eye and some may require a telescope.  Many of the objects listed will require a map of the sky to find or may require repeat observations to notice various properties.  Links to star charts and other information that will be useful in identifying the objects listed will be given at the end of each week’s section. 

For December we will be doing things a little different.  Instead of highlighting a constellation for December we will be tracking down some of the closest stars to the Sun.   Observing projects like this are a good way to refine your observing skills.  They also serve as a nice alternative for when you want something more than the same old faint fuzzies you have been looking at for the last few months.  All of the stars chosen for this month will be visible in binoculars and some will be visible to the naked eye. 

Week one of our expedition through our stellar neighborhood will bring us to two of the closest and brightest stars in the sky; Sirius and Procyon.  These two stars are found in the winter circle and will be visible by 10:00 p.m. 

Sirius is the brightest star in the night sky shinning at magnitude -1.74 and it is the 6th closest to the Sun.  It is a white A-Class hydrogen fusing star.  It has a smaller and hotter companion known as Sirius B that has evolved into a white dwarf star at the end of it existence.  Sirius B is the remnant core of a more massive star that was likely 5 to 7 times more massive than the Sun.  All that remains of Sirius B is a dense hot core of carbon and oxygen.  This dense core is only 0.92 times the size of Earth and shines with a luminosity of 2.8 percent of the Sun’s total output.  Sirius B is very difficult to see due to the intensely bright glare of its partner Sirius A. 

Procyon is the 8th brightest star in the night sky shining at a magnitude of 0.34 and it is the 15th closest star to the Sun.  Like Sirius, Procyon is a binary system with the main component star (A) being a hot white F-Class star and the secondary star (B) is a white dwarf star at the end of its life.  Both of the white dwarfs discussed in this section are two of three white dwarfs that helped identify and understand what white dwarfs actually are.

To find both Sirius and Procyon, look for Orion the Hunter and his famous three belt stars.  Once you have found the belt follow the three stars to the left of the belt and the brightest star you see will be Sirius.  Looking east of the belt will bring you to Procyon in Canis Minor.  Both of the stars are members of what many observers call the Winter Circle.  This is a group of stars that circles Orion and helps identify most of the winter constellations.  For those just beginning with backyard astronomy this structure is in my opinion the best place to start.  Use the maps below to help identify the star Sirius and Procyon. 



For the week of December 9 we will visit the 10th nearest star, Epsilon Eridani.  It is a K2-Class orange star that currently is in its main sequence.  The temperature of this star is roughly 5,000 K making it just a bit cooler than the Sun.  Epsilon Eridani is not much smaller than the Sun but it only shines with about 35% the luminosity of the Sun.  At that luminosity and a distance of 10.5 light years, Epsilon Eridani appears as a 3.73 magnitude star in our southern skies. 

Epsilon Eridani has been the focus of a number of studies.  Since the 1930’s this star was believed to either have a companion or to be a potential candidate for a nearby star that has a planet.  The companion theory was disproven but in 1985 a circumstellar debris disc was discovered.  Observations of this dusty debris ring showed evidence of clumping that was suggestive of a large body orbiting the star.  Since the 1980s radiometric observations were been done that indicated there was a large body perturbing Epsilon Eridani.  From 2001 to 2003 the Hubble Space Telescope joined the hunt and confirmed that there is indeed a planet orbiting Epsilon Eridani.

The SETI program also considered Epsilon Eridani a star of interest.  The SETI program or the Search for Extraterrestrial Intelligence included Epsilon Eridani as a target for their radio telescopes hoping to find signals that would indicate an advanced civilization may live on a planet orbiting the star.  No such signal has been found yet but SETI is still strong and actively searching the skies for the signal that most want to believe is out there. 

Epsilon Eridani has also been the focus of a number of studies interested in developing alternative propulsion methods with the hopes of sending a ship to a nearby star.  Current methods of propulsion cannot provide the thrust needed to get a spacecraft to a nearby star in a human lifetime.  For decades now scientists have been looking into new methods to get us to stars like Epsilon Eridani.  The Deadelus and Icarus programs included Epsilon Eridani as a target star that could be reached using one of their alternative methods.  Various designs including nuclear fusion, fission and laser propulsion have been suggested to get a spacecraft to Epsilon Eridani within a human lifetime.  These ship designs are purely theoretical but still remain as likely ways humanity will be able to visit our stellar neighbors in the future.

Epsilon Eridani is found in the constellation Eridanis the River.  This constellation starts at the celestial equator and heads south out of view from us here in St. Louis.  The part of Eridanis we can see is found just south and west of the constellation Orion.  Finding Epsilon Eridani starts with finding the bright stars Saiph and Rigel at the bottom of Orion.  Draw a line extending from Saiph to Rigel and follow that line roughly 20 degrees to the west.  Doing this you will see four stars ranging in brightness from 2nd to 3rd magnitude.  These four stars form a crooked line of stars and the west most of these stars is Epsilon Eridani.  Use the maps linked below to find the guides stars and Epsilon Eridani.  There will also be links to the relevant programs discussed above.





For the week of December 16 we will visit 61 Cygni, the 16th closest star to the Sun.  Let’s start with the fact that 61 Cygni is not one but two stars.  The stars in this binary system take 659 years to orbit each other and are 44 to 124 AU (1 AU = 93,000,000 miles) apart depending on where they are in their orbits.  Together they appear as one star to the naked eye making them the 4th closest star visible without the aid of a telescope or pair of binoculars. However, using a pair of binoculars will split 61 Cygni into its two component stars.  The three naked eye stars that are closer are those discussed in the previous weeks.  61 Cygni A and B are both Orange K-Class stars that are smaller, cooler and older then the Sun.

The 61 Cygni system has also been dubbed Piazzi’s Flying Star due to its large proper motion in the sky.  Careful observations of this star through an entire year will reveal that this pair of stars is moving through the sky.  Even though all stars are moving most are far enough away that detection of their proper motion is not possible through backyard instruments.  Stars like 61 Cygni that have high proper motions and are close to us allow us to monitor their movement through the Milky Way by carefully monitoring them in respect to the background star fields.    

To find 61 Cygni first locate the Summer Triangle.  The three stars that make the Summer Triangle are Deneb, Vega and Altair.  These bright stars can be seen in the western skies about 40 minutes after sunset.  Once you can see the triangle focus on the star Deneb.  This is the tail star of Cygnus the Swan and will be your starting point for finding 61 Cygni.  From Denib start scanning to the east and you will see two pairs of stars within 10 degrees of Deneb.  The first pair stars are the Xi and Nu Cygni and the second pair is Sigma and Tau Cygni.  These four stars range in brightness from 3.5 to 4.5 magnitude and should be visible to the unaided eye.  West of Sigma and Tau Cygni using binoculars you will see a fainter pair of stars.  The northern star of this pair is 61 Cygni.  Even though the directions sound complicated, finding 61 Cygni is not very difficult.  The key is to use a good map of the sky.  61 Cygni is visible to the unaided eye but in light polluted areas you will be better off using a pair of binoculars.


2013 Year of the Comet Part II

Earlier in the year we talked about 2013 as being year of the comet.  In the spring we had Comet PANSTARRS and for the end of the year we mentioned Comet ISON that was first predicated to become visible to the naked eye and had the chance to become as bright as the full moon.  Well, so far the year of the comet has not panned out as people were hoping for.  Comet PANSTARRS was supposed to become visible to the naked eye but for most it remained just beyond naked eye visibility.  It was still quite beautiful through binoculars and telescopes but it did not break the naked eye threshold for most observers. 

Perihelion for Comet ISON has now come and gone.  Like many comets ISON failed to survive its close approach to the Sun.  As a consolation for the demise of Comet ISON there are two other comets you can see in the morning skies.  These comets are named Lovejoy (C/2013 R1) and Linear X1.  Comet Lovejoy is easy to see in binoculars and Linear X1 will require a telescope.  Find out more information about these two comets and the demise of Comet ISON below.

General Comet Information



Star Charts Showing Comet Locations in the Sky




Demise of Comet ISON



Comet Update 12/02/2013:

Comet Lovejoy (C/2013 R1): This comet remains a great comet through a pair of binoculars and can now be found in the constellation Bootes. It is shining at magnitude 4.6 making it an easy target in a pair of binoculars and should be visible to the unaided eye away from city lights.  Use the finder chart above to locate this comet.

Comet Linear X1: This comet is hanging at 9th magnitude so it should still be visible in small telescopes.  Use the link above to find daily locations for this comet.

NASA Mission of the Month

Each month we will be celebrating a NASA mission of the month.  This month’s mission is the Solar and Heliospheric Observatory (SOHO).  This is a telescope that dedicates it’s time to observing the Sun.  Telescopes like SOHO and its predecessor the Solar Dynamics Observatory (SDO) have revolutionized the fields of solar physics and stellar astronomy.  Our understanding of how the Sun functions has changed dramatically since the launch of SOHO.  In addition to the Sun, SOHO has helped observe comets, asteroids and anything else that moves within its field of view.  It is a fascinating telescope that provides us with a front row seat to the most important object in our solar system.  To learn more visit


50th Anniversary of the James S. McDonnell Planetarium

2013 marks the 50th anniversary of the James S. McDonnell Planetarium.  There are a number of events planned for the year that will celebrate the 50th anniversary.  For more information about the planetarium and the 50th anniversary, visit www.slsc.org

Our next Star Party will be held on Friday, January 3, 2014, from dusk until 10 p.m.

Weather permitting, the St. Louis Astronomical Society and the Science Center will set up a number of telescopes outdoors and be on-hand to answer your questions.  Telescope viewing begins at 8:00 p.m.  Regardless of the weather on January 3, join us indoors in our planetarium theater for “The Sky Tonight”.  Showtime is at 7 p.m.  As there is a 7 p.m. star show there will be only one Laserium show on all First Fridays.  This show begins at 8:30 p.m.  Information for laser shows can be found at http://www.slsc.org/laserium

This free, indoor star program will introduce you to the current night sky, the planets, and the seasonal constellations. Doors open 15 minutes before show time. Shows begins at 7 p.m. Sorry, no late admissions due to safety issues in the darkened theater.

The St. Louis Astronomical Society hosts the monthly Star Parties at the Science Center which are held on the first Friday of each month. Our Monthly Star Parties are open to the public and free of charge.  For more information about the St. Louis Astronomical Society visit their website at www.slasonline.org


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