Week of August 26, 2013

This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Monday, August 26.  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, September 6, 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 6:25 a.m. on Monday, August 26 and sunset is at 7:40p.m. providing us with under 14 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 9:14 p.m. this week.  For those with a sun dial, solar transit or local noon occurs around 1:03 p.m. this week. 

Moonrise for Monday, August 26 is at 10:55 p.m. and moonset is at 1:19 p.m. on the following day.  The Moon will be exhibiting a waning gibbous phase with roughly 66% of the lunar disk illuminated.  Last quarter moon occurs on August 28.      

International Space Station (ISS) Observing

There is only one visible pass of ISS over St. Louis for the next two weeks. See the table below for information regarding this pass.  If this single pass doesn’t satisfy your hunger for satellite observing, there are a few iridium flares coming up that will be quite good for us in St. Louis.  If you have an interest in observing these iridium flares follow this link.

http://www.heavens-above.com/IridiumFlares.aspx?lat=38.62722&lng=-90.19778&loc=Saint+Louis&alt=135&tz=CST

Catch ISS flying over St. Louis in the evening hours starting Monday, August 26. 

Date

Mag

Starts

Max. altitude

Ends

Time

Alt.

Az.

Time

Alt.

Az.

Time

Alt.

Az.

27 Aug

-0.8

20:48:08

10

NNW

20:50:11

15

NNE

20:52:13

10

ENE

           

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 Virgo and will set by 9:10 p.m. 

Mars

Mars is finally out of the Sun’s glare rising at 3:34 a.m.  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 2:22 a.m. becoming visible roughly 30 minutes later.  It is currently paired with Mars in the morning skies. 

Saturn

Look for the ringed planet shortly after sunset high in the south.  Currently Saturn is found in the constellation Virgo just to the east of the bright star Spica.  Saturn will set by 10:25 p.m.

 

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. 

As this is our last full month of summer we will do things a bit different.  This month we will cover some of the overlooked constellations of the summer sky.  These will be the smaller minor constellations that are often lost amongst the larger more famous constellations.  Each week we will add a constellation to look for and a few of its highlights.

The first of our overlooked constellations will be Sagitta the Arrow.  There seems to be some debate as to what arrow this is supposed to represent but most seem to agree it is an arrow relevant to the story of Aquila the Eagle.  This was Zeus’s eagle that pecked at Prometheus nightly as a punishment for stealing fire from the gods and giving it to humankind.  Sagitta the arrow is believed to be either the arrow that Hercules used to kill Aquila saving Prometheus from this eternal torture or the arrow that Aquila carried in his talons.

To find Sagitta look for the bright Summer Triangle containing the three stars Denib, Vega and Altair.  Once you have found Altair look about 8 degrees north of the bright star and there will be five star s that look like a small arrow.  Sagitta is one of the smallest constellations so it will be easy to miss. Using the star chart linked below you should have no problem identifying this small group of stars.

It may be small but Sagitta has a number of interesting objects to look at.  One of these objects is the eclipsing binary (EB) called U Sagittae.  This is a pair of stars that orbits one another in such a way that they eclipse each other from our perspective.  During the primary eclipse of the pair the star will fade in brightness from 7.9 to 9.2 magnitude. U Sagittae’s minima will last for a little more than one hour.  The primary eclipse of this EB star occurs every 3.25 days.  It will be a suitable target for binoculars and small telescopes.  To find U Sagittae look 5 degrees west of Alpha Sagittae and then 1.75 degrees to the north.  This will be a tough find but well worth the effort.  It is one of the better EB stars in the northern hemisphere. 

Another interesting object in Sagitta is the globular star cluster M71.  It is a class X-XI cluster meaning it is a very loose globular cluster according to the Shapley-Sawyer ranking system.  It has the mass of approximately 17,000 stars that are found to be roughly 13,000 light years away from us. 

Shining at a magnitude of 8.2, M71 is a target for a good pair of binoculars or a small telescope.  It will be easy to find as it is directly between the bright stars Delta and Gamma Sagittae.  Pan back and forth between these stars and you should have no problem finding M71.

Sagitta may be small but it is loaded with goodies for the careful observer.  Get a good map for Sagitta and there are many other things to look for besides the two we listed.  Unfortunately most of these objects are best viewed through a telescope.

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

http://messier.seds.org/m/m071.html

The next overlooked constellation is Vulpecula the Fox.  Vulpecula is one of the newer constellations having been named by the Polish astronomer Johannes Hevelius in 1687.  For those that found Sagitta last week all you have to do is look above Sagitta and you are in Vulpecula.  Cygnus lies directly to the north of Vulpecula. 

Even though Vulpecula is relatively large there are not a lot of deep sky objects to look for.  That being said, one of the best planetary nebulas is found in the fox.  Known as M27 or the Dumbell Nebula this deep sky object offers us a look into the Sun’s future demise.  Most are familiar with how large stars end which is an event called a supernova.  Stars like the Sun are not massive enough for this to occur and instead will shed off its outer layers dwindling down to a white dwarf star.  This is the future of the Sun in roughly five billion years.  The material that low mass stars shed off tends to be seen as a symmetrical cloud of dust and gas, this is what astronomers call a planetary nebula.  M27 was the first planetary nebula to be discovered.

To find M27 you need to find Gamma Sagittae which is the brightest star at the tip of the arrow.  Look about 3 degrees to the north and you will find M27.  Lying at a distance of 1,250 light years, the dumbbell nebula shines at a magnitude of 7.1 meaning that in moderate viewing conditions it can be seen in a pair of astronomical binoculars (10x50).  It will be best seen in telescopes with wide fields of view as it covers an area of 6 arc minutes. 

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

http://messier.seds.org/m/m027.html

The overlooked constellation for the week of August 19 is Delphinus the Dolphin.  Delphinus was the dolphin that carried the Greek poet Arion to the shores of Tarentum allowing him to escape the pirates that were perusing him.

Delphinus lies east of Sagitta and south of Vulpecula.  It will be easier to spot then the two previously listed constellations owing to a small collection of bright stars in a diamond and triangle shape.  Outside of this small group of stars the rest of Delphinus is relatively faint. 

Due to being a small constellation, Delphinus only has a few objects that are reasonably easy to find if you have a good star chart.  We will start with a collection of multiple star systems.  The first double star to stop at is Gamma Delphini.  This star marks the nose of the dolphin and is easily seen to the unaided eye.  This binary system is a pair of stars that are separated by roughly 9 arc seconds.  Gamma Delphini is easily split with small telescope using about 35x.  **Magnification is not something you should worry about when buying a telescope but it is something that you should be familiar with for double star observing. ** You change the magnification of your telescope by changing the eyepiece.  To calculate your telescope’s magnification you need to divide the focal length or your telescope by the focal length of the eyepiece. (ex. Focal length of telescope = 1000mm/eye piece = 25mm; 1000/25 = 40x magnification)  I will include a link to an article that will cover this topic in greater detail. 

If you are enticed by the Gamma Delphini double then try the double star Struve 2725 and the triple star Struve 2703.  Both of these are split using a telescope at about 50x.  Struve 2725 is found just below Gamma Delphini in the same field of view and Struve 2703 is found between the stars Beta and Zeta Delphini near the tail of the dolphin.  Use the linked maps below to find these stars.  In the second map Struve 2725 and 2703 will not be named but will be represented as a small dot with a horizontal line through it near the larger guide stars listed. 

There are a few globular clusters and planetary nebulae in Delphinus but they will be tough finds if you are observing in light polluted conditions.  For those interested in trying their hand at finding these deep sky objects look up information for NGC 6934, 7006, 6891 and 6905.  Be aware you will need a telescope for these and will likely have to leave the lights of St. Louis to find them.

This week there is a special observing project available to anyone with a pair of binoculars.  When choosing the constellation for this week there was a bit of astronomical serendipity that occurred.  After choosing Delphinus it was announced that a new nova star had been discovered in the dolphin.  Nova stars are a type of variable star that typically involve a binary system with the primary star being a white dwarf and the secondary being a cooler low mass star.  As they orbit each other the white dwarf star accretes or steals material from its companion.  This material builds up and when the temperature and pressure is high enough a thermo-nuclear event occurs.  This explosion causes the star to flare in brightness by about 10 magnitudes.  On August 14th Koichi Itagaki discovered the nova star Del 2013 shining at a magnitude of 6.8.  Over the next few days astronomers around the world followed Del 2013 as it continued to brighten to about 4.5 magnitude.  It was last reported at 4.8 magnitude and will likely remain here for the next few days.  Many novae will only be seen once in a human lifetime so try and see it while the seeing is still good.  Novae typically flare dramatically in brightness and then slowly fade back out of view.  You should have at least a week to see Del 2013 through just a pair of binoculars.  For those interested in observing this rare sight use the second map linked below.

Update 8/26/2013: Del 2013 is now shining at roughly magnitude 6.  This will make it difficult in city skies to spot it in a pair of binoculars.  Small telescopes will still get the job done and with moonlight no longer a major issue it should still be visible through most telescopes.

http://www.iau.org/static/public/constellations/gif/DEL.gif

http://media.skyandtelescope.com/documents/Nova_in_Delphinus_PSA64.pdf

http://www.telescopes.com/telescopes/magnificationandusingeyepiecesarticle.cfm

The Final constellation for August is Scutum the Shield.  Like Vulpecula, Scutum is a modern constellation named in 1690 by astronomer Johannes Hevelius.  It is located south of Aquila the Eagle and north of Sagittarius.  To find Scutum, locate the diamond shape of Aquila and identify the brightest star in the constellation named Altair.  From Altair star hop down to Delta Aquilae then to Lambda Aquilae.  Once you are at this point look for a small diamond shaped grouping of stars and you have found Scutum.

The best object to look for in Scutum is the open star cluster M11.  This young group of 2,900 stars is estimated to be roughly 220 million years old and is approximately 6,000 light years away.  Shining at an apparent magnitude of 6.3, M11 is visible in binoculars and will be spectacular at low powers through most telescopes.  M11 is one of the richest and most spectacular of the open clusters visible in the northern hemisphere.  To find M11 locate the star Beta Scuti and look about two degrees the southeast.  When observing through a telescope some of the brightest stars in the cluster form a V-shape.  It is because of this that M11 is also called the Wild Duck Cluster.

M11 is one of six open clusters in Scutum.  There is also a globular cluster, planetary nebula and reflection nebula to look for as well.  I would recommend spending some time in Scutum while it is still high in the evening skies.

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

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

http://messier.seds.org/m/m011.html

As you can see that even though these constellations were small and not very prominent in our skies, they contain lots of goodies that make them worth our time.  When you are learning to find the bigger and brighter constellations take the time to scan your star charts to see what other little gems you may find in the same area. 

NASA Mission of the Month

Each month we will be celebrating a NASA mission of the month.  This month’s mission is the Mars Science Laboratory (MSL).  The MSL rover now called Curiosity was launched on November 26, 2011 and successfully landed on Mars August 5/6, 2012.  It is a mission that will be exploring the habitability of the Martian environment looking for evidence that it could have supported life in the past.  To learn more about the MSL mission visit

http://mars.jpl.nasa.gov/msl/

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, September 6, 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 September 6, join us indoors in our planetarium theater for “The Sky Tonight”.  Showtime is at 7 p.m. (Please note this time changed from 8:00 p.m. to 7:00 p.m. due to Laserium starting a 8:30 p.m.)  

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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