Week of October 21, 2013

This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Monday, October 21.  All times are given as local St. Louis time (Central Daylight 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, November 1, 2013 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 7:16 a.m. on Monday, October 21 and sunset is at 6:14 p.m. providing us with 11 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 7:43 p.m. this week.  For those with a sun dial, solar transit or local noon occurs around 12:46 p.m. this week. 

Moonrise for Monday, October 21 is at 8:04 p.m. and moonset is at 10:44 a.m. on the following day.  The Moon will be exhibiting a waning gibbous phase with roughly 92% of the lunar disk illuminated. Last quarter moon occurs on October 26.

International Space Station (ISS) Observing

The next visible passes of ISS over St. Louis are all evening passes.  The best passes are on the evenings of October 26, 27 and 29.  See the table below for information regarding these passes.

Catch ISS flying over St. Louis in the evening hours starting Monday, October 21. 

Date

Mag

Starts

Max. altitude

Ends

Time

Alt.

Az.

Time

Alt.

Az.

Time

Alt.

Az.

21 Oct

-0.3

20:24:20

10

NNW

20:24:39

12

NNW

20:24:39

12

NNW

22 Oct

-1.2

19:36:23

10

NNW

19:38:21

16

NNE

19:38:21

16

NNE

23 Oct

-0.9

18:48:29

10

NNW

18:50:04

13

NNE

18:51:39

10

NE

23 Oct

-0.6

20:24:11

10

NW

20:25:01

16

NW

20:25:01

16

NW

24 Oct

-2.2

19:36:03

10

NW

19:38:49

30

NNE

19:38:49

30

NNE

25 Oct

-1.7

18:47:58

10

NNW

18:50:36

21

NNE

18:52:42

13

ENE

25 Oct

-0.8

20:24:17

10

WNW

20:25:38

22

WNW

20:25:38

22

WNW

26 Oct

-3.4

19:35:53

10

NW

19:39:14

82

NE

19:39:38

66

ESE

27 Oct

-2.9

18:47:35

10

NW

18:50:49

46

NE

18:53:48

12

ESE

27 Oct

-0.5

20:25:02

10

W

20:26:45

17

WSW

20:26:45

17

WSW

28 Oct

-1.5

19:36:04

10

WNW

19:39:03

30

SW

19:41:08

16

S

29 Oct

-2.6

18:47:24

10

WNW

18:50:42

58

SW

18:53:58

10

SE

30 Oct

 0.2

19:38:07

10

WSW

19:38:32

10

SW

19:38:56

10

SW

     

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:

http://www.jpl.nasa.gov/

The Planets Visible Without A Telescope

Venus

The brightest planet in the sky is well into another evening apparition becoming visible about 30 minutes after sunset.  Venus will be low to the horizon and any trees or buildings west of you may obscure it from view.  Venus is currently seen in the constellation Ophiuchus and will set by 8:21 p.m. 

Mars

Mars is out of the Sun’s glare and will rise around 2:46 a.m. this week.  For those awake around 4:00 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 it 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.

Jupiter

The largest planet in our solar system has returned to our skies.  This week it will rise around 11:09 p.m. becoming visible roughly 30 minutes later.  It is currently paired with Mars in the morning skies. 

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. 

The constellation for October will be Cepheus the King.  In Greek mythology Cepheus is best known as the husband of Cassiopeia and father to Andromeda.  These three are famously part of the story of Perseus.  Cepheus was also one of the Argonauts that sailed with Jason as he quested for the Golden Fleece. 

Usually Cepheus is listed as part of the fall sky but in reality from St. Louis he is visible year round.  Cepheus is part of our circumpolar which means it never rises or sets but rather just circles around the North Star.  If the stars were visible in the daytime, Cepheus would always be visible.  The easiest way to find Cepheus is to star hop from Alpha to Beta Cassiopeiae and keep heading to the north.  Look for an elongated upside down house shape of stars.  The house shape extends almost to the North Star. 

The first object we will cover in Cepheus is the variable star Delta Cephei.  This star is the prototype Cepheid variable.  It is a giant yellow star that due to internal pulsation will flare in brightness then fade back down to its normal magnitude.  The cause of these pulsations is not confirmed but one theory suggests that Cepheids are stars that have an internal struggle between the outward pressure of radiation and the internal pull of gravity.  Due to increasing and decreasing temperatures the balance of these forces ebb and flow causing the star to expand and contact. 

Cepheid variables also have a special place in astronomy as the period of their pulsations is directly related to their absolute brightness which in turn can be used to measure how far away the star is.  This period luminosity relationship was discovered by one of astronomy’s unsung heroes.  Her name was Henrietta Swan Leavitt and she was hired on as a computer at the Harvard College Observatory in 1893.  Regardless of her advanced education Henrietta was held back from academic careers in astronomy as in those days it was primarily seen a male prerogative.  In 1912 she was cataloging variable stars in the Small Magellanic Cloud and found 25 of them to be Cepheids.  When she arranged them in order of periods she discovered that the longer the period was the brighter the star was.  This discovery was one of the most important in modern astronomy.  Using Henrietta’s period luminosity discovery and his discovery of a Cepheid in what was then known as the Andromeda Nebula, Edwin Hubble was able to prove that the Andromeda Nebula could not be a nebula in the Milky Way but instead must be a galaxy beyond ours.  In essence what Henrietta did for astronomy is she gave astronomers the tool that opened the universe to our understanding.  For this critical discovery she received little to no recognition.  So when you look to Delta Cephei this month remember this and think of Henrietta Swan Leavitt and maybe do your part to teach people about this unsung hero of astronomy.

Delta Cephei varies in its brightness over a period of 5.366 days.  It changes from 4.4 magnitude to 3.5 magnitude in about one and half days then fades back to 4.4 magnitude slowly over a period of four days.  Both the maxima and minima are bright enough to be seen without the aid of a telescope or binoculars.  Owing to this and the short time it takes to brighten then fade, Delta Cephei is a great beginning target for those interested in variable star astronomy. 

To find Delta Cephei use Cassiopeia to find the house shape of Cepheus.  Next locate the stars Alpha and Gamma Cephei.  These are the two stars that mark the bottom of the house shape of Cepheus.  If you look closely at Gamma Cephei you will notice it is part of a little triangle shape of stars.  The star that marks the peak of this little triangle shape as it extends away from Cepheus is Delta Cephei.  Use the maps linked below to help you find this gem of the northern skies.  I will also include links to the AAVSO site for further reading about Cepheid variables and Henrietta Swan Leavitt. 

http://iau.org/static/public/constellations/gif/CEP.gif

http://www.aavso.org/files/vsots/0900.pdf

http://www.aavso.org/henrietta-leavitt-%E2%80%93-celebrating-forgotten-astronomer

The object for the week of October 7 is the star Mu Cephei.  Also known as Herschel’s Garnet Star, Mu Cephei is a long period pulsating red supergiant star.  In other words it is a star at the end of its life and is pulsating internally as it begins the process leading to a spectacular explosion called a type II supernova.  With a diameter roughly 1,600 times greater than the Sun’s, Mu Cephei is the third largest star discovered.  It is also one of the most distant stars visible to the naked eye.  It is believed that Mu Cephei has a total luminosity of 600,000 times the Sun’s.  On top of all this it is one of the reddest stars in the sky which is why Herschel called it the Garnet Star.

To find this fascinating star look between the stars Alpha and Zeta Cephei that mark the bottom of the house shape described above.  About halfway between them you will notice a star with a distinct reddish hue to it.  This is a star to keep an eye on as it will change its brightness from nearly 5th magnitude up to about 3.5 magnitude.  Unfortunately it does this about every 2 to 2.5 years.  Not the best of variable stars but worth a look.  For further help finding Mu Cephei and for additional information follow the links below.

http://iau.org/static/public/constellations/gif/CEP.gif

http://www.aavso.org/vsots_mucep

http://www.astroscience.org/abdul-ahad/Mu_Cephei.html    

The object for the week of October 14 is the open star cluster NGC 188.  This open star cluster is a grouping of roughly 120 observed stars that lie at a distance of 5,400 light years.  NGC is listed at 8.1 magnitude which would normally put it within the limit of a decent pair of binoculars.  Unfortunately NGC 188 is quite far away and its light is very diffuse meaning that any city lights will wash this star cluster from view.  Dark skies are a must and in reality most will need a telescope to see this cluster but it is worth the effort. 

NGC 188 stands out amongst its brighter brethren as it is extremely old for an open star cluster.  Most open clusters are made up of hot O, B and A class stars that use up their hydrogen at extreme rates.  Due to these stars gluttony they only last a few million years before they leave their main sequence becoming red supergiants and soon after will reach the end of their stellar lives.  NGC 188 is made up of mostly cooler and smaller G and K class stars similar to the Sun.  Due to their smaller and cooler nature the stars of NGC 188 are roughly 5 billion years old.  In addition to their long stellar lives the stars in NGC 188 lay above the plane of the Milky Way galaxy.  Due to its location there is less gravitational interaction with the main mass of the galaxy.  Most open clusters orbit much further into our galaxy’s mass which results in a cluster being pulled apart. 

To find NGC 188 use the Big Dipper to locate the North Star Polaris.  This star is not in Cepheus but lies near its northern boundary.  Once you have found Polaris just look 4 degrees away.  Use the chart linked below to find this elusive but fascinating star cluster.

http://iau.org/static/public/constellations/gif/CEP.gif

The object of the week of October 21 is the multiple star system ξ (Xi) Cephei.  Laying roughly 100 light years away Xi Cephei is a fine multiple star system even for light polluted skies.  Separated by 8 seconds of arc, Xi Cephei is easy to split using only 60x magnification with most telescopes.  Remember upping a telescopes magnification is done by changing eyepieces.  The two stars you will see will have different colors.  Normally I would describe what colors you would see but in researching the star numerous different colors have been suggested so instead I will let you decide for yourself.  What you will see is a 4.5 star with a fainter 6th magnitude companion.  The primary star is an A- Class star so it should be a bluish white star and the secondary star is a F-class star so it should appear white.  Stars frequently have different apparent colors due to dust and other factors scattering or affecting how we perceive their colors.  Due to this, reports describing these stars have described them as yellow, orange, blue and violet.  Take a look at this fine pair of stars and see what you think their colors are. 

Xi Cephei is not two but three and perhaps even four stars.  The third companion is too close to the primary to be seen in backyard telescopes.  It is another F-class star that takes roughly 810 days to orbit the primary star in this system.  Some also suggest that there is a 4th companion to this system but it is not confirmed if it is a star that lies in the line of sight with Xi Cephei or if it is a true companion.  If it is a true companion it would take roughly 80,000 years to orbit the primary star. 

To find Xi Cephei locate the house shape of Cepheus as described above.  In the middle of the house there is a 4th magnitude star, this is Xi Cephei.  It will be the brightest star you see inside the house so there should be no confusing it.  While you are looking at Xi Cephei try looking 5 degrees further south.  Not far from Xi Cephei is a fantastic five star system called Struve 461 that will be a challenge but will be visible using the same magnification used to split Xi Cephei.  Use the links below to help you locate the multiple star systems described for this week.

http://iau.org/static/public/constellations/gif/CEP.gif

http://bestdoubles.wordpress.com/2010/07/28/beautiful-xi-cephei-guides-you-to-a-nearby-5-star-multiple-%CE%BF%CF%83461/     

NASA Mission of the Month

Each month we will be celebrating a NASA mission of the month.  This month’s mission is the historic and current Cassini/Huygens mission.  This mission launched on October 15, 1997.  It reached orbit around Saturn in 2004.  The primary mission lasted until 2008 and included detailed studies of Saturn’s rings, its moons with special interest in the moons Titan and Iapetus, Saturn’s atmosphere and its magnetosphere.  The primary mission also included the Huygens probe which successfully landed on the moon Titan transmitting images and information as it descended to the surface.  The Cassini mission was extended to the year 2010 and was renamed the Cassini Equinox Mission.  This extension was designed to study Saturn during its equinox.  As Cassini reached the end of the Equinox mission it was once again extended.  This time called the Cassini Solstice Mission its focus is to now study the Saturnian system during its solstice.  This mission extension will end in 2017 with two close flybys of the moon Titan.  The first will alter the orbit of the spacecraft so it passes a mere 3,000 km above the clouds of Saturn and the second will send the spacecraft on a trajectory that will see it plunge into the atmosphere of Saturn.  By its end Cassini will have been in space for 20 years giving us new insight to the Saturn and Jupiter systems, the heliosphere and a better understanding of the solar system as a whole.  To learn more visit www.nasa.gov or http://www.esa.int/ESA and search for Cassini.      

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, November 1, 2013, 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 November 1, 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

http://www.slsc.org/laserium

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