Week of April 29, 2013

This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Monday, April 29.  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, May 3, 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 6:06 a.m. on Monday, April 29 and sunset is at 7:51 p.m. providing us with over 13 hours of daylight.  Even after sunset, the light from the Sun will still illuminate our sky just over 1.5 hours.  This period of time is called twilight, which ends around 9:31 p.m. this week.  For those with a sun dial, solar transit or local noon occurs around 12:58 p.m. this week.

Moonrise for Monday, April 29 is at 11:20 p.m. on the preceding day and moonset is at 9:28 a.m. on the following day.  On Monday, April 29 the Moon will be exhibiting a waning gibbous phase with roughly 80% of the lunar disk illuminated.  Last quarter moon occurs on Thursday, May 2. 

International Space Station (ISS) Observing

There are no visible passes of ISS until May 16, 2013.

There are numerous other satellites visible during this rare dry spell of ISS passes.  Visit http://heavens-above.com/?lat=38.62722&lng=-90.19778&loc=Saint+Louis&alt=135&tz=CST to learn more about other satellites that will be visible.  If you are not in St. Louis you will need to reset the viewing location on the website linked.  As for what satellites to look for; I would recommend Tiangong1or Iridium Flares.

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 planet Jupiter will be visible shortly after sunset and sets around 10:49 p.m.  Grab a pair of binoculars and see how many of the Galilean moons you can see.  Depending on when you look you should be able to see all four; Io, Europa, Ganymede and Callisto.  As you watch them sketch their locations relative to Jupiter and you will be following in the footsteps of Galileo.


Look for the ringed planet shortly after it rises around 7:32 p.m. this week.  Currently Saturn is found in the constellation Libra just to the west of the bright stars Zubeneschamali and Zubenalgenubi.  Saturn reached opposition on April 28.  It is now at its brightest and will remain visible until November. 

May-June Planetary Grouping

At the end of May and beginning of June, there will be a fantastic grouping of planets low in the western skies.  In late May, Mercury and Venus both begin their next evening apparitions.  They eventually join Jupiter in the western skies shortly after sunset.  As we get closer to this conjunction more information will be posted.  For now read this article and start preparing for this celestial display.


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 Ursa Minor.  Also known as the Little Bear, this constellation can be found in the circumpolar sky.  The term circumpolar indicates that the stars which make up the constellation never really rise or set but rather circle around the North Star.  Due to its location in the circumpolar sky, Ursa Minor is visible all year long.  The name Ursa Minor comes from the ancient Greek interpretation of this star pattern.  The story involves a Nymph of the Moon goddess Artemis named Callisto.  She was wooed by Zeus and gave birth to a son named Arcas.  Fearing the anger of Artemis and his wife, Zeus turned Callisto into a bear.  One day her son was hunting and came across a great bear who unbeknownst to him was his mother.  As he knocked his arrow and took aim, Zeus intervened and turned Arcas into a bear.  Now a bear, Arcas recognized his mother and the two were then placed into the sky together safe from hunters and the ire of Hera.  This story led to the formation of Ursa Minor (Arcas) and Ursa Major (Callisto).

To find Ursa Minor locate the Big Dipper high in the northern skies.  Using the two stars at the end of the dipper’s bowl, trace a straight line above the bowl until you find Polaris.  This will be the brightest star in Ursa Minor.  Once you have found Polaris use the star chart linked below to find the rest of the stars of Ursa Minor. 


Object of the week for April 29 is the Little Dipper.  Even though the Little Dipper is well known to most, it is not nearly as easy to find as most would think.  Frequently people think that the star cluster M45 (Pleiades) is the Little Dipper.  It does indeed look like a small spoon but it is never seen in the north.  The common method used to find the Little Dipper is to use the last two stars in the bowl of the Big Dipper.  Just like was mentioned above, follow a straight line above the Big Dipper’s bowl and this will take you to the North Star.  The North Star is the last star in the Little Dipper’s handle.

The little dipper also serves as a good lesson in light pollution.  In cities most of the stars in the Little Dipper are very difficult to see due to light pollution drowning out their light.  The more stars you can see in the Little Dipper, the better your viewing conditions will be.  It is also important to mention that if you leave North America, it is no longer called the Little Dipper.  Both the Big and Little Dippers are not constellations but rather are asterisms.  These are informal groupings of stars as apposed to the formal groupings we call constellations.

Lastly, the Little Dipper was chosen for our first object in May as it will serve as our reference point for the rest of the month.  Most of the objects we will cover in May are visible in just a pair of binoculars but they will be considerately more difficult to find.  It is important to have a strong reference point to base our explorations from.                       

NASA Mission of the Month

Each month we will be celebrating a NASA mission of the month.  This month’s mission is the Hubble Space Telescope.  This telescope is named after the famous astronomer Edwin Hubble who showed us that the universe was huge and was expanding at exceeding rates.  This discovery revolutionized astronomy.  Much like the astronomer, the telescope continues to push our understanding of the universe and allows astronomers to see some of the most distant objects ever observed.  The Hubble Space Telescope has been in space now for over 20 years and has made over 1 million observations.  It continues to shed light on the universe and its origin.  To learn more about the Hubble Space Telescope 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, May 3, 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 May 3, 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 shows 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 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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