Week of Monday, July 14

This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Monday, July 14.  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, August 1, 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 5:48 a.m. on Monday, July 14 and sunset is at 8:25 p.m. providing us with nearly 15 hours of daylight.  Even after sunset, the light from the Sun will still dimly illuminate our sky for about 2 hours.  This period of time is called twilight, which ends around 10:18 p.m. this week.  For those with a sun dial, solar transit or local noon occurs around 1:07 p.m. this week.     

Moonrise for Monday, July 14 occurs at 9:58 p.m.  Moonset will occur at 9:40 a.m. on the following day.  On Monday, July 14 the Moon will be exhibiting a waning gibbous phase with roughly 92% of the lunar disk illuminated.  Last quarter moon occurs on July 18 this week at 9:08 p.m.      

International Space Station (ISS) Observing

This week visible passes of ISS will be in the early morning hours.  The best of these will occur on the July 16 and 20.  To learn more about this pass and others this week use the information below.

Catch ISS flying over St. Louis in the morning starting Monday, July 14. 

Date

Mag

Starts

Max. altitude

Ends

Time

Alt.

Az.

Time

Alt.

Az.

Time

Alt.

Az.

15 Jul

-1.4

04:23:25

15

S

04:25:12

22

SE

04:27:53

10

ENE

16 Jul

-0.7

03:37:07

12

SE

03:37:07

12

SE

03:38:34

10

ESE

16 Jul

-3.0

05:10:06

10

WSW

05:13:26

64

NW

05:16:47

10

NE

17 Jul

-3.2

04:23:41

30

SW

04:25:10

71

SE

04:28:31

10

NE

18 Jul

-2.2

03:37:19

36

ESE

03:37:19

36

ESE

03:40:07

10

ENE

18 Jul

-1.6

05:10:54

10

W

05:13:47

26

NNW

05:16:41

10

NNE

19 Jul

-0.4

02:50:54

13

E

02:50:54

13

E

02:51:27

10

E

19 Jul

-2.3

04:23:48

23

W

04:25:26

40

NNW

04:28:38

10

NE

20 Jul

-3.0

03:37:21

66

N

03:37:21

66

N

03:40:31

10

NE

20 Jul

-0.7

05:12:26

10

NW

05:14:26

15

NNW

05:16:26

10

NNE

21 Jul

-1.0

02:50:53

23

ENE

02:50:53

23

ENE

02:52:19

10

NE

21 Jul

-1.0

04:23:47

12

WNW

04:26:00

19

NNW

04:28:32

10

NNE

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

Venus is now well within its current morning apparition. It rises around 3:52 a.m. becoming easily visible by 4:30 a.m.  Venus is currently exhibiting a gibbous phase with roughly 60% of the Venusian disk illuminated.

Mars

Mars is now in the constellation Virgo and rises before the Sun sets.  For those awake around 9:00 p.m. you will see a reddish-orange object high in the southern skies.  We have now passed by Mars in our orbit and will continue to move further away each day.  Mars will set by 12:28 a.m. 

Saturn

Saturn has reached opposition and thus will rise before the sun sets.  Look for it in the southeast about 30 minutes to an hour after sunset depending on how clear your southeastern skies are.  Saturn will remain with us until 1:43 a.m.  It forms a nice triangle in the sky with Libra’s two brightest stars Zubenelgenubi and Zubeneschamali. 

If you watch Saturn in relation to these two stars you will notice it is exhibiting retrograde motion.  This is caused as the Earth catches up with a planet and then passes it by.  During this we see the planet from changing angles making it appear to move westward and then eastward again. This motion is more prevalent with planets closer to us such as Mars.  If you go outside once a week for the rest of the year and sketch where Saturn is in relation to Zubenelgenubi and Zubeneschamli you will see this retrograde motion. 

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 July will explore objects in the constellation called Lyra the Harp.  This constellation is one of those that are part of the bright asterism known as the Summer Triangle.  It contains the bright star Vega which is one of the three stars that make the bright triangle.  The Summer Triangle acts as a beacon for observers during the summer months helping us find other constellations and the objects they contain.  Due to the visibility and usefulness of the triangle, the constellation Lyra is one of the first visited by many observers during the summer months. 

The ancient Greeks imagined this small bright grouping of stars as the lyre that Apollo gave to his son Orpheus.  After the death of his wife Eurydice, Orpheus played his lyre impressing Hyades the god of the underworld.  Hyades was so impressed that he allowed Eurydice to follow Orpheus out of the underworld provided that Orpheus not turn back and look at her until they were safely out.  Orpheus at the last minute could not resist and when he turned back to look she was gone forever.

Lyra is also the home of one of the best meteor showers we see every year.  The Lyrid meteor shower is caused as the Earth annually plows through debris left by Comet Thatcher.  The first recorded observation of this meteor shower dates back to 687 BCE when Chinese astronomers recorded what appeared to be stars falling out of the sky in April.  April is the peak month to view the Lyrids with a peak date of April 22.

http://meteorshowersonline.com/lyrids.html

The crown jewel of Lyra is the bright star Vega.  This beautiful star is an A-class star meaning it will appear blue white in color.  The temperature of Vega is about 9,600 Kelvin making it about 1.7 times hotter than the Sun.  It is only twice the mass of the Sun but because of its higher temperature it is about 40 times more luminous.  This makes Vega one of the most luminous stars in the Sun’s galactic neighborhood.  As Vega is more massive and hotter it will only exist about one tenth as long as the Sun.  That is the nature of the bigger and brighter stars. 

One interesting feature of Vega is its location along the path that the Earth’s northern axis follows during the precession of the equinoxes.  This process is caused because of the Earth’s oblate shape and the tidal forces applied to our planet by the Sun and Moon.  As a result of these two factors the Earth wobbles causing our axis to trace out a cone shape.  This changing orientation causes the north polar axis to be orientated towards different stars.  We do not have to worry about a changing North Star as the precession process takes 26,000 years to complete one full wobble.  This equates to about one degree of motion per year.  In about 12,000 years Vega will become the Earth’s North Star. 

To find Lyra and its crown jewel all you have to do is look east about 45 minutes after sunset.  Doing this you will see three bright stars which form the Summer Triangle asterism mentioned above.  The other two stars in the triangle are called Denib and Altair.  As twilight begins to fade you will notice a parallelogram shape of stars just below Vega.  This is the main pattern people use to identify Lyra the Harp. 

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

The first object we will cover in Lyra is the beautiful planetary nebula called M57 or the Ring Nebula.  Planetary nebulae are the remnants of stars like the Sun as they begin to evolve.  The Sun and all stars start out fusing the hydrogen at their cores.  From this process atoms of helium are produced along with some energy which eventually becomes the light we see emitted by stars.  Like our cars or any device that consumes a material component it will eventually run out of this “fuel” source.  Once the Sun runs out of its core hydrogen its core will begin to collapse and the outer layers will expand and cool.  Due to its collapse core temperature will rise until the helium that has been collecting at the core begins to fuse.  Again the core will run out of its “fuel” and collapses until it is hot enough that carbon and oxygen can fuse.  This stage is called a white dwarf and it is where most stars will end their stellar lives. At this stage all that is left is a much smaller but hotter core.  For a brief time this high temperature allows the dying star to excite the gasses around it creating a beautiful fluorescing cloud of gas and debris.  This is what is called a planetary nebula.  When we observe M57 we are looking at the Sun’s distant future. 

To find M57 first locate the star Vega and the parallelogram shape below it.  Once you have identified the parallelogram shape of stars you need to identify the two southern most stars in this shape.  They are named Beta and Gamma Lyrae.  Using a telescope scan between these two stars and you will find a distinct ring shaped source of light.  This is the planetary nebula M57. 

M57 shines with a magnitude of 8.8 which means it is dim enough that we do need a telescope to observe it.  It is possible that big binoculars will spot it but M57 is roughly one arc minute across causing it to appear very small through wide field devices.  Because of this giant binoculars that have the resolving power to see this nebula would only reveal a small star like object.  If you do not have your own telescope, look up your local astronomy clubs.  Astronomy clubs, museums and many universities will host observing nights that are free to anyone.  Here in St. Louis we have three active astronomy clubs.  All three of them host numerous observing nights one of which is our First Friday observing program.  Below you will find links to the astronomy clubs in St. Louis and more information about M57.

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

http://messier.seds.org/m/m057.html

http://www.slasonline.org/

http://www.asemonline.org/

http://stemideas.org/outreach-projects/star-gazing/

The object for the week of July 7 is the star Delta Lyrae.  There are a few reasons I wanted to cover this star in the night sky update.  First it is a double star.  Unlike those in the past this double is not physically a pair but rather is called an optical double.  These two stars happen to appear close together but are actually about 200 light years apart.  Frequently you will see them listed as Delta-1 and Delta-2.  Delta-1 is a bright B-Class hydrogen fusing star that has a temperature of 18,000 Kelvins.  This puts Delta-1 at nearly 3000 times hotter than the Sun.  Delta-2 is about 200 light years closer to us and is an M-Class red giant star.  Delta-2 is about 7 times more massive than the Sun and is about 300 times larger than the Sun. 

The bright red color of Delta-2 and the blue color of Delta-1 give the pair a very nice color contrast making them an attractive pair to seek out.  In addition to the color contrast Delta-1 is a member of an open star cluster called Stephenson 1.  This is a cluster that is not very well detached from the background stars and it has less than 50 component stars. 

In addition to Delta-1 & 2 you can also try to find another red star called SAO 67546.  This is another member of the Stephenson 1 cluster that is a K-class red giant star that will have an orange hue.  Both Delta-2 and SAO 67546 are stars on their way to becoming white dwarfs that could produce planetary nebulae like M57 discussed last week. 

To find the optical double star Delta Lyrae and the associated Stephenson 1 star cluster first find the bright star Vega.  Once you have identified Vega look for the parallelogram shape of stars below the bright star described last week.  This time we want to use the northern two stars of the parallelogram shape.  These stars are called Zeta and Delta Lyrae.  The latter of the two being our target star. 

Those with sharp vision will be able to determine that Delta Lyrae is two stars.  The distinct color of the two stars and the Stephenson 1 cluster can be seen clearly through a simple pair of binoculars.  The best view of the cluster will be through a telescope using a low magnification eyepiece.  Reference the map linked below for help finding Delta Lyrae and the associated Stephenson 1 star cluster.

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

The object for the week of July 14 is the multiple star system Epsilon Lyrae.  What looks to be a 4th magnitude star near Vega is really the combined glow of four separate stars.  Last week we covered a similar multiple star called Beta Lyrae but Epsilon is different in that its member stars are gravitationally bound to one another.  In other words Epsilon Lyrae is a binary system.  Careful inspection of Epsilon Lyrae will reveal two stars using just your eyes.  For those of us with less than perfect vision a pair of binoculars will plainly reveal what looks like two bright white stars.  The western of the two is Epsilon 1 and the eastern of the two is Epsilon 2.  Epsilon 1 and 2 are separated by roughly 10,000 AU (AU = 93 million miles; average distance between Earth and Sun) and are estimated to take nearly 400,000 years to orbit each other. 

Using a decent telescope at moderate magnification Epsilon 1 and 2 can each be split into two stars.  Splitting Epsilon 1 and 2 is easy because they are about 200 seconds of ac apart.  Splitting the two pairs is a bit more difficult because they are only a few second of arc apart.  A moderate sized telescope will work you will just have to bump up the magnification.  The Epsilon 1 pair is labeled 1A and 1B and the Epsilon 2 pair is labeled 2C and 2D.

All four stars are A-class stars with temperatures that range from 7700 kelvins to 8200 kelvins.  At these temperatures the stars shine with a white to bluish white color.  The stars have masses at 1.9, 1.5, 1.9 and 1.8 solar masses making them main sequence white dwarf stars. These are not the same as the white dwarf discussed above with M57.  The white dwarf related to M57 is a highly evolved star that has shed its outer layers revealing a small dense core that is fusing carbon and oxygen.  Main sequence white dwarfs are young hydrogen fusing stars that are still in their prime.

The stars in the Epsilon Lyrae system are approximately 800 million years old.  For the time being they are gravitationally bound but as they move through the Milky Way the pairs will likely separate into two separate double star systems.  Finding Epsilon Lyrae is pretty simple as it is right next to the bright star Vega.  Once you find Vega all you have to do is look about 2 degrees to the east and you will see Epsilon Lyrae.  If you deal with light pollution or diminished vision you will likely need binoculars to spilt the wide pair.  To spot all four stars you will need a telescope.  Depending on how large your telescope is you will need moderate to high magnification to split all four.  If you have an interest in finding more double or multiple star systems there are numerous other options this time of year.  Sky and Telescope has some very nice articles that will help you find many more doubles and more importantly help you refine your observing skills that are required to find and observe this type of object.  Below you will find links to these articles and the IAU map of Lyra.

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

http://www.skyandtelescope.com/observing/celestial-objects-to-watch/double-stars/  

Our next Star Party will be held on Friday, August 1, 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 August 1, join us indoors in our planetarium theater for “The Sky Tonight”.  Showtime is at 7 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

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