Ryukyu Astronomy Club Newsletter
Volume 1, Issue 7 September 2002

Next Club Meeting - September 14th
Conference Room B at the Camp Lester Naval Hospital

August Meeting
The August meeting of the Ryukyu Astronomy Club was held on the 10th in the Navy Hospital's Conference Center.  There were 8 in attendance.  John O' Briant gave a great presentation on Kitt Peak National Observatory in Arizona.  John and his family visited there recently during their vacation.  In addition to a slide show with many great pictures and tons of information, John also distributed some brochures from the site.

Also in attendance was a guest, Gene Dolphin, who gave a presentation on auroras and the Fairbanks ice festival.  Gene had a slide show with many wonderful photos from a couple of trips to Fairbanks and recommended that if anyone was interested in making such a trip, the best time is March as this coincides with one of the annual peaks in aurora activity as well as the ice festival.  Gene also mentioned that his son is a profession astronomer currently working for the National Optical Astronomy Observatory (NOAO), the government organization responsible for operating and overseeing Kitt Peak.  And all coming together in Okinawa, Japan...truly a small world.

Afterwards several club members traveled to Maeda Point.  Tommy McGee and John O'Briant brought their 80mm computerized goto scopes and everyone enjoyed the view before the clouds rolled in.

Things to See This Month
The Sun has been putting on quite a show the last few months.  Several very large sunspots, many times the size of the Earth, have been visible recently.  If you have a solar filter for your binoculars or telescope, don't miss the show.  As always, when viewing the Sun, be sure to be extra cautious, even a brief exposure of unfiltered sunlight can permanently damage your eyesight.

September is about the best month to spend some time taking in the many great sights in the heart of our galaxy - the Milky Way.  The constellations Sagittarius and Scorpius hold a wondrous variety of nebula and star clusters.  Most locations in the United States, Europe and mainland Japan do not allow for the views we enjoy of this area of the sky here from Okinawa.  This section of sky is too low and close to the horizon for those farther north, but Okinawa is far enough south that Sagittarius is well-placed to show off its treasures.

Look to the south after sunset to locate the "teapot" and start scanning with a pair of binoculars.  From a dark site the view is incredible.  With a little practice, you should be able to find open clusters like M6 and M7 and one of the most spectacular globular clusters in the sky, M22.  Step up to the telescope and the list grows longer:

For more objects of interest and the locations of those listed above, download the latest chart from or visit and customize the online star chart for Okinawa's general location of 128 degrees East longitude and 26 degrees North latitude.

Magnitude - Measuring Brightness 
More than two thousand years ago, the first recorded attempt to quantify the brightness of sky objects was undertaken by the Greek astronomer Hipparcos.  His scale of measurement varied from first to sixth magnitude.  First magnitude stars were the brightest he could see, while sixth magnitude were the faintest.  As the science of astronomy progressed, the magnitude system was refined to allow precise measurements of all celestial objects.  For example, Venus is brighter than the brightest star and reaches a magnitude of more than -4 at times.  The brightest star in the sky, Sirius, is magnitude -1.  From a dark, clear site, the faintest stars most can see are magnitude 6, just as Hipparcos designated.  The following chart estimates the magnitude limits visible in various sized instruments under dark skies.



Limiting Magnitude

Naked eye

About 7mm









60 mm (2.4 in.)



80 mm (3.1 in.)



4 in.



114 mm (4.5 in)



5 in.



8 in.



11 in.



14 in.


A difference of 1 in magnitude is actually a difference of 2 1/2 in brightness.  Thus, the difference in brightness between a magnitude 2 star and a magnitude 4 star is 6.25 - 2 1/2 times 2 1/2.  This explains why larger and larger instruments only gain fractional improvements in limiting magnitude.  Nonetheless, these fractional differences are significant.  The relatively modest step of just 1 magnitude difference between a 5 inch and 8 inch telescope brings many thousands of faint deep sky objects into view.

We can estimate the magnitude of naked eye objects using a couple of the most recognizable star formations in the sky.  For viewers in the Northern Hemisphere, turn to the Little Dipper.  In the Southern Hemisphere, refer to the Southern Cross.  The magnitudes of their various stars are shown in this figure:


Magnitude figures for deep sky objects are not as clear-cut as those for stars and planets.  Generally the entire luminosity of the object is “summed up” and reported as if it were a single point light source (a star).  So, a very large object of several arcminutes could be reported with a fairly bright magnitude, but appear very faint in the eyepiece.  This is typically the case for nebulae and galaxies.  Consider the Andromeda Galaxy, M31.  It is generally reported as approximately magnitude 3.4, but that 3.4 is spread out in an area of about 180 by 60 arcminutes.  This is about 6 times the width of the full moon!  So, while a star of magnitude 3.4 is easily visible to the naked eye, M31 requires dark clear skies to be glimpsed without optical aid.

In the case of deep sky objects, a better measure of luminosity is "surface brightness".  Surface brightness is not standardized and thus varies from one recorder to another, but is generally a measurement of magnitude per square arcsecond.  Thus we can better compare deep sky objects and determine whether we should be able to view them in our telescope or binoculars.  One slight complication for using surface brightness is the fact that not all objects are uniformly bright across their entire surface.  Again consider M31.  The core is many times brighter than the surrounding spiral arms.  Thus, the surface brightness of the core is higher than the average surface brightness of the entire galaxy.

RAC Messier Award
Announcing the new Ryukyu Astronomy Club Messier Award!  Viewing the Messier objects is a great introduction to the night sky.  Upon observing 70 of the 110 Messier objects, you will receive a certificate and your name will be posted on the club web site.  We are still finalizing the details, but you can get started now.  All observations must be logged on or after September 1, 2002 and you must submit an electronic copy of your observations for each object (the format of the log will be available at our web site).  Details will be posted at our web site and we will send out an announcement when this section is ready.  A list of the 110 Messier objects can be found in the Downloads section of our web site.

Clear Skies!

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