Week of Monday, June 24, 2013

This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Monday, June 24.  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, July 5, 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 5:38 a.m. on Monday, June 24 and sunset is at 8:29 p.m. providing us with nearly 15 hours of daylight.  Even after sunset, the light from the Sun will still illuminate our sky for nearly two hours.  This period of time is called twilight, which ends around 10:27 p.m. this week.  For those with a sun dial, solar transit or local noon occurs around 1:04 p.m. this week. 

Moonrise for Monday, June 24 is at 9:33 p.m. and moonset is at 8:16 a.m. the following day.  On Monday, June 24 the Moon will be exhibiting a waning gibbous phase with roughly 98% of the lunar disk illuminated.  Last quarter moon occurs on June 29.

International Space Station (ISS) Observing

ISS passes over St. Louis for the next two weeks starting Monday, June 24 are evening passes.  Unfortunately we are headed into a dry spell for ISS passes.  After June 25 we will not see ISS again until July 15.  This will be a good opportunity to try and spot some of the other satellites passing overhead.  There are a couple of good morning passes for Tiangong 1 on June 30 and July 2.  Here is a link to information regarding passes of Tiangong 1

http://heavens-above.com/PassSummary.aspx?satid=37820&lat=38.62722&lng=-90.19778&loc=Saint+Louis&alt=135&tz=CST

Catch ISS flying over St. Louis in the evening hours the week of Monday, June 24. 

Date

Mag

Starts

Max. altitude

Ends

Time

Alt.

Az.

Time

Alt.

Az.

Time

Alt.

Az.

24 Jun

-0.9

21:59:20

10

W

22:01:18

15

SW

22:02:49

12

SSW

25 Jun

-1.7

21:09:53

10

WNW

21:12:43

27

SW

21:15:33

10

SSE

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 Gemini and will set by 10:00 p.m. 

Mars

Mars is finally coming out of the Sun’s glare during the hours of morning twilight.  It rises about one hour before the Sun which means for most it will be difficult to find.  For those awake around 5:00 a.m. look to the east and you may find 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.

Saturn

Look for the ringed planet shortly after sunset low in the southeast.  Currently Saturn is found in the constellation Virgo just to the east of the bright star Spica.  Saturn will set by 2:29 a.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. 

This month our constellation is Scorpius.  This is a prominent summer constellation that is rising by 9 p.m. and is above the horizon around 11 p.m.  Why focus on a something that becomes visible so late?  Unfortunately due to the growing daylight and twilight hours, we do not have dark skies until after 10 p.m.

Scorpius is one of the twelve zodiacal constellations.  Zodiac constellations were created by ancient astronomers to track the movement of stars that appeared to wander amongst the other stars.  They noticed that the wandering stars always followed a specific path in the sky.  Today we call this the ecliptic and the wandering stars we now know as planets.  Also found along the ecliptic are the Sun and Moon meaning that Scorpius and the other zodiac constellations are visible anywhere on the Earth.     

The name Scorpius comes from the ancient Greeks who saw this as the giant scorpion that killed the great hunter Orion.  Owing to the fact that Scorpius is visible around the world, there are numerous other interpretations for this grouping of stars.  One of my favorites comes from ancient Polynesia in which many of the ancient islanders believed this was the giant fishhook the Sky Father plunged into the oceans to pull up the islands. 

To find Scorpius look almost due south after 11:00 p.m. and you will find a large and bright fishhook shape of stars.  The first star in Scorpius you see through the veil of twilight is the red supergiant Antares.  Many people see this as the heart of the scorpion and it is our first stop in Scorpius. 

http://www.iau.org/static/public/constellations/pdf/SCO.pdf    

Object of the week for June 3 is the bright star Antares.  Also known as Alpha Scorpii, this is the brightest star in Scorpius and the 15th brightest in the sky.  It is unmistakable as it has a distinct reddish orange color.  The reddish color indicates the star is a red supergiant nearing the end of its stellar life.  In optical light Antares is 10,000 times brighter then the Sun.  Due to a cool surface temperature of 3600 Kelvin, Antares radiates a great deal of light in the infrared wavelength.  If you account for this, Antares is a whopping 60,000 times brighter then the Sun.  Antares lies approximately 550 light years away, is 15 to 18 times more massive than the Sun and has a radius of 3.4 AU (one AU = 93 million miles; average distance between Sun and Earth).  Due to its high mass, Antares will likely develop an iron core that will lead to a violent core collapse resulting in an explosion called a type II supernova

Antares is also a double and a variable star.  Both features will be difficult to observe but are worth looking in to.  Antares is a semi-regular variable that only changes by a few tenths of a magnitude.  The companion to Antares a hot B-class star called Antares B which lays only 550 AU away.  At this distance, Antares B is fully immersed in the solar wind from Antares.  With an angular distance of less than 3 arc seconds it will require at least a 6-inch telescope to resolve the companion.  If you are successful in splitting the pair you should notice that Antares B has a greenish color that is the result of a color contrast caused by the bright reddish light from Antares.

Object for the week of June 10 is a globular star cluster called M4.  This is one of 156 globular star clusters found in the Milky Way galaxy.  M4 is one of the closest globular clusters to us lying at a distance of roughly 7,200 light years away.  Its age is estimated to be roughly 12.2 billion years old making it one of the oldest structures in the Milky Way.  It orbits the galaxy once every 116 million years passing through the galactic plane from time to time.  Due to tidal forces, this cluster sheds stars each time it passes through the galactic plane.  Currently it has a mass of about 67,000 solar masses which is low compared to other globular clusters.  Using the Hubble Space Telescope scientists have peered into the heart of this globular and found a stellar graveyard.  The center of this cluster has a number of white dwarf stars which are the dense carbon/oxygen cores of low mass stars that at the end of their lives.  It is estimated that M4 has upwards of 40,000 white dwarfs which will likely be used to refine its estimated age.  M4’s Shapley-Sawyer classification is XI indicating it is a loosely concentrated globular star cluster. 

To find M4 look for Antares discussed last week and then scan about 1.4 degrees to the west.  M4 has a magnitude of 5.6 making it just barely visible to the unaided eye if observing from dark locations.  It is an easy find in binoculars and will resolve into individual stars through a 4-inch instrument.  Looking closely you can see a bar-like structure of stars extending through the center of the cluster.  M4 is a fascinating look into the distant past of the Milky Way.  It will be visible all summer long and is a great deep sky object for beginning observers.

http://messier.seds.org/m/m004.html

Object for the Week of June 17 is the open star cluster M7.  This star cluster also known as Ptolemy’s cluster, is roughly 800 light years away and has a mass of roughly 735 solar masses.  To the naked eye M7 appears as a faint patch of nebulous light that was first recorded by Claudius Ptolemy in his treaties on astronomy called the Almagest.  Through binoculars you will start to resolve some of the brightest stars and through a telescope you can count 30 to 80 individual stars.  A number of the stars in M7 are double stars and on the western edge of the cluster there is a much more distant and faint globular cluster called NGC 6453.  Also in the cluster is a planetary nebula called PK356-4.1 but this will require dark skies and a large telescope to see.

M7 is simple to find once Scorpius has fully risen above the horizon.  First look for the tail of the scorpion or barb of the fishhook shape.  The two brightest stars in the barb are Shaula and Lesath.  Once you have found this part of Scorpius look about 4 degrees northeast of Shaula and you will easily see this bright star cluster.  M7 is a great deep sky object for those just starting to explore the sky’s deep sky wonders.

http://messier.seds.org/m/m007.html  

Object of the week of June 24 is a variable star called Dschubba or Delta Scorpii.  Found in the head of the scorpion, Dschubba is a star that normally shines at a magnitude of 2.32.  This puts it at the 5th brightest star in Scorpius.  Back in 2000, variable star observers were making brightness estimates of stars listed as having a constant brightness.  One observer noted that one of these stars Delta Scorpii had brightened by roughly 1/10 of a magnitude.  To the average observer this change would not have been noticeable but to veteran variable observers this was big.  They continued to watch this star over the next couple of years the star continued to brighten peaking at near 1st magnitude making it the second brightest star in Scorpius.  Since then Delta Scorpii has remained this bright with sudden dips in brightness that quickly end seeing the star return to the brighter state as quickly as the dimming occurred.  This complex light curve generated by the flare event and the short periods of variability are due to the complex nature of Delta Scorpii. 

Delta Scorpii is a BE-star.  This is a late evolutionary stage of rapidly rotating hot B-type (blue) subgiant stars as they leave their main sequence phase of their lives.  BE-stars rotate extraordinarily fast and as a result they lose matter from their equatorial regions creating a disk of material around the star.  BE-stars are hot enough that they ionize this disk of material and interstellar gasses extending about 10 light years away from the star.  Another clue to the sudden flaring of this star comes from the fact that it is a binary system containing four stars.  From this point on we will refer to them as δ Sco A (main component), B, C and D.  Of these four, δ Sco C is about the distance between the Sun and Saturn (~ 9.6 AU) from δ Sco A making an orbit every 10 years.  This star is of particular interest as in the year 2000 when Delta Scorpii started to flare, this companion star reached it periastron which is the closest point in its orbit to δ Sco A.  This flare and periastron relationship between δ Sco A & C was confirmed in 2011 when δ Sco C completed another periastron.  In 2011 Delta Scorpii flared again reaching a magnitude of 1.6.  What is likely happening is gravitational forces caused by δ Sco C as it orbits δ Sco A strengthen as it reaches periastron triggering a greater amount of mass loss from δ Sco A. In return we see more material being ionized causing the star we see to brightened significantly. 

Currently Delta Scorpii stands at roughly 1.9 magnitude.  The quicker more subtle light variations are not completely understood yet and will require further observations.  If you would like to monitor this star for future light variations you will need to have a map of the sky indicating magnitudes of the surrounding stars.  The trick to variable star observing is to use stars with magnitudes similar to the maximum and minimum brightness of your target star.  Linked below will be a map from the American Association of Variable Star Observers (AAVSO) that will list numerous photoelectric magnitudes of stars around Delta Scorpii in addition to marking a handful of other variable stars around Scorpius.  Also found below will be an AAVSO article describing the complex nature of BE-stars and the discovery that Delta Scorpii was one of them.  You will not need a telescope for this project but it will be best to observe from a dark location if at all possible.  For further variable star information go to AAVSO to learn about the different types of variable stars and to find current observations made by members of AAVSO.  Be warned, variable star observing can be difficult at first but once hooked it becomes very addictive.  You may find yourself daydreaming thinking about variable stars and their light curves. 

Stellar Magnitude Map

http://www.aavso.org/vsots_delsco

NASA Mission of the Month

Each month we will be celebrating a NASA mission of the month.  This month’s mission is the historic Gemini Program.  The Gemini Program lasted from 1962 to 1966; it included 10 manned flights and was the intermediary program between the Mercury and Apollo programs.  The Gemini program was needed so NASA could learn more about long duration space flights and their effects on astronauts; develop rendezvous and docking methods with other orbiting space craft; perfect reentry and landing methods; and learn more about the effects of weightlessness on astronauts and their physiological reactions.  These four Gemini mission objects were crucial for getting astronauts to the Moon and back.  Project Gemini doesn’t always the credit it deserves but without it the Apollo missions would not have happened.  To learn more about Project Gemini visit http://www-pao.ksc.nasa.gov/kscpao/history/gemini/gemini.htm

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.

Our next Star Party will be held on Friday, July 5, 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 July 5, 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.)

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 8 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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