The monthly meeting of the Ogden Astronomical Society will be held this Thursday July 10, 1997 in the Ott Planetarium star chamber on the Weber State University campus. This meeting will come to order at its usual time of 7:30 p.m.

A favored member of the local astronomical community, friend of the O.A.S. and former Director of the Hansen Planetarium, Mr. Von Del Chamberlain will share a special evening with the members and friends. Among his many focuses in the science over the years, Von Del has collected a unique assortment of meteorites. He will bring select samples of his collection to the July meeting and discuss their meaning and their origin. Issues relating to Earth's history and future aspects for meteoric impacts will likely be hot topics of discussion.

ANTELOPE ISLAND SHOULD OFFER BETTER SKIES IN JULY

Members will come together near the shores of the Great Salt Lake again this month. Saturday July 12, at White Rock Bay is the place. The last Antelope Island event was something of a soggy story. However, with the improving conditions the island should present the best seeing, for members and the public, to date.

Most of the bugs should be gone by now so a tailgate party sounds even better than before. Members and friends can come early to enjoy solar viewing and join the munch-bunch before dark. Scopes are needed to entertain the multitudes who show up. There are only two Antelope events left after this one so come and enjoy while we can.

HARMON'S CENTER IN OGDEN IS SCHEDULED FOR O.A.S. & PUBLIC

On Saturday July 19, O.A.S. members can assemble their telescope equipment in the outer parking lot of the Harmon's store at 2nd Street and Washington Blvd. For this, the third in the series of public outreach star parties, members can display their knowledge and observing talents through the lights of central Ogden. Want an observing challenge? This will work. Come, join the members before the sun sets so visitors and passers-by can eyeball the telescopes and ask questions before nightfall. Details on this and the other July star parties will be available at the July 10 meeting.

It seems like a long time since the last Monte Cristo star and tea party. That is because it has been a long time, eleven months to be exact. As was discussed in an earlier issue of The Star Diagonal, there will be only one official club event at Monte this year.

Friday and Saturday August 1 and 2 are the official dates of this year's event. As in years past of course, many members will likely arrive on Wednesday or Thursday in order to snag that best camp site for the weekend.

The Pot Luck feasts will be held on both Friday and Saturday nights at one of the camp sites in loop "E". We will not know which site is the lucky one until we get there, so stay tuned.

Arrangements have been made with the U.S. Forest Service for limited vehicular access to the meadow. Part of the club's agreement with the Forest Service is that overnight camping is not allowed in the meadow. Members and friends are asked to comply with this agreement. A Keep-It- Clean policy is in effect at all times in the forest. Carry it In and Carry it Out while in the meadow is the policy of the day.

Come and join the fun at the one and only Monte Cristo event for 1997. For further details come to the July 10 meeting or call Steve, Elgie, Bob or Doug.

Members should ponder what they could offer the club by considering nomination to a position on the Executive Committee. September is the Annual Meeting of the O.A.S. and will see the election of F.Y. 1997-98 officers. The nominating committee will be appointed soon and will seek enthusiastic folks with ideas and a will to lead. Make yourself known by contacting the committee first. Let your voice be heard.

It's Summer, kids. No more cold weather excuses for not getting out under the stars. Mosquitos are only in the mind. Get the dust off those lenses, there's plenty to see the month. From July 7 to August 7 we will witness a grazing occultation of Aldebaran, an asteroid in the "Coat Hanger", an excellent opportunity to see a 6.9 magnitude star while the Sun in still above the horizon, and, as August breaks, enjoy another Monte Cristo Star Party. Let's get to the details.

The first featured event this month occurs on the night of July 16-17 when magnitude 9.6 asteroid 2Pallas crosses the famous "Coat Hanger" asterism [a.k.a. Collinder 399] in Vulpecula (The Fox). Perhaps this configuration of stars has escaped your attention. Like the Pleiades, the Coat Hanger does not entirely fit the field of view of a telescope, even at low power. It is best viewed using binoculars. Once the Coat Hanger is located, you may want to switch to a telescope to zero in on Pallas (see insert in fig. 2). The star just west of Pallas has a magnitude of 9.5. For comparison, most of the stars in the asterism range from magnitude 5.2 to 7.0. Figure 1 and 2 show the location of the Coat Hanger relative to Cygnus and Sagitta and the position of Pallas at midnight. You may want to locate the asteroid on the nights prior to the 16^th and a few night thereafter to follow Pallas' progress and convince yourself this is not a star. On the 16^th Pallas' apparent speed will be 31.655" per hour at position angle 244.7. Pallas is one of the largest asteroids with an estimated diameter of 523 km. For some, this may be the first time you have seen an asteroid; it probably won't be the last.

As it negotiates its path across the Celestial Sphere, the Moon can be found anywhere in a band approximately 10 wide. Within this band there are a number of bright stars that can be occulted by the Moon, but none brighter than Aldebaran, the "Eye of the Bull'. Occultations of Aldebaran are not rare events; two have occurred over the past few months (April 10 and June 4). Grazing occultations of Aldebaran for a particular location on Earth are much more infrequent.

On the morning of July 29 viewers in most of the United State will again witness an occultation of Aldebaran. Some locations in Utah will get a special treat, a grazing occultation. Consider Aldebaran as a light source casting a shadow of the Moon on the Earth. Observers located at the edge of this shadow will see Aldebaran blink off and on as its light is intercepted by a succession of mountain peaks on the Moon's edge. Ogden observers will not see an occultation at all, being located north of the Lunar shadow. Those observing from Provo will witness an occultation (from 3:40:36 to 3:49:07 MDT), but not a graze. Somewhere in between these cities astronomers will be on the "graze line". Based on information obtained from the website of the International Occultation Timing Association (IOTA), the graze line passes through the following coordinates:

110°30.0'W, 411.66'N and 11230'W, 4015.55'N. The first point is the town of Oakley on the road between Wanship (off route 80) and Kamas. The second point is Lewiston Peak at the south end of the Oquirrh Mountains. Drawing a line between the two points we find the graze line passes about two miles south of the Draper golf course and about a mile north of Point of the Mountain on Interstate 15. The line also passes through the south end of Park City.

If you plan to rise early on the morning of the 29^th to observe the occultation, keep one thing in mind when chosing your site, Aldebaran will be only 13.5 above the horizon. Its azimuth will be 79.9. If you plan to view from sites like Park City or Oakley, be sure the mountains won't block your view by checking out the site before the event.

This event is of prime interest to IOTA and it must be noted that IOTA will be meeting at Utah Valley State College Planetarium at 9:00 a.m. on July 27, partially for the purpose of planning for the observation and timing of this event. The public, especially the amateur astronomy community is invited to attend. Interested persons may vistit IOTA's website at http://www.sky.net/~robinson/iotandx.htm or contact UVSC's Paul Mills at millspa@uvsc.edu )for additional information.

Incidentally, even if you are not planning to observe at the graze line, IOTA is interested in receiving video tapes of the event to assist in refining our knowledge of the Moon's profile. The Moon's precise dimensions are used during total eclipses of the Sun to determine cyclic changes in the Sun's diameter. These changes in turn may be helpful in the study of global warming. IOTA needs to know the observers location to an accuracy of 50 feet and the exact time of the disappearance and reappearance of Aldebaran. You may use the distance your observing site is from a street intersection to pinpoint the location. For timing, it is suggested you keep your camcorder running following the disappearance and reappearance of the star long enough to go indoors and record at least two minutes of The Weather Channel (don't connect your camcorder to the TV or VCR but point the camera directly at the TV screen. In the Salt Lake area the entire event can easily be recorded in one contiuous segment as long as that segment includes the disappearance, reappearance and two minute portion from the Weather Channel. An alternate timing method is to take advantage of a broadcasted time signal which can be picked up by the camcorder's microphone. Information on where these tapes can be sent can be obtained from David Dunham, President of the IOTA at dunhamdw@space2.spacenet.jhuapl.edu.

As some OAS'ers know I have logged a number of daytime hours at the eyepiece. Talk about light pollution! For the most part, this consists of viewing the planets, Moon and Sun. About five years ago I read that the twenty or so brightest stars can be observed in the daytime with optical aid. The first of these stars I observed was Vega. Being surprised at how easy this observation was, I became curious to see just how faint a star I could capture with my 8" SCT. Referring to Peterson's Field Guide, "Stars and Planets" list of "brightest stars to magnitude 3.5" I began to seek out progressively fainter stars. Fainter than mag. two, I found it difficult to find individual stars. It was time for a change of strategy. It was discovered at this time that double stars were much easier to locate, especially when one of the components is very bright. I switched to Peterson's list of double stars. Eventually, I perfected my technique to the point of detecting a star magnitude 7.8, the B component of double star 39 Draconis on July 25, 1993.

In July conditions are favorable to observe another faint star in the daytime, (Xi) Bootis B. Not a record-breaker at 6.9 magnitude, but still a challenging and very satisfying observation. Believe it or not, Boo is not that hard to find with the Sun up. Very conveniently this double (with a 4.7 mag. primary) has a declination almost identical to that of Arcturus ( Boo). Arcturus' declination is +1911' while that of Xi Boo is +1906'. A telescope with settings circles will be needed and a clock drive is very useful but not essential. Your scope must be polar aligned. This can be done on the night before the observation or during the daytime using the "solar drift" method. I do not have space here to describe the solar drift method in detail, but will provide personal assistance to anyone not familiar with the technique.

The "trick" in finding Xi Boo B is to first find Arcturus at R.A. 14:15.7+1911' and center it in the field. Next, lower the scope 5' to the declination of Xi Boo. At this point, set the R.A. circle to Arcturus' right ascension. Be sure Arcturus' image is in sharp focus. Now slowly slew the telescope eastward to Xi Boo's R.A., 14:51.4. With a bit of patience you will see Xi Boo A's image drift across the field. Center Xi Boo and readjust the focus. The B component is at a position angle of 318 and 6.6" from the 4.7 magnitude A component. At that PA, B will be found roughly northwest of A. If all goes well you will see the faint image of the 6.9 magnitude target. Good luck!

This month images are of Pluto the ninth planet. Pluto's orbit about the Sun is more elliptical and more steeply inclined to the plane of the ecliptic than is the orbit of any other planet. In fact, Pluto's orbit is so eccentric that this planet is sometimes closer to the Sun than Neptune is, now for example. Pluto has one moon Charon (pronounced KAR-en).

Pluto Data

Mean distance from Sun: 39.53 AU=5.914 x 10to9 km

Maximum distance from Sun: 49.53 AU=7.381 x 10to9 km

Minimum distance from Sun: 29.72 AU=4.446 x 10to9 km

Mean orbital velocity: 4.7 km/s

Sidereal period: 248.5 years

Rotation period: 6.387 days

Inclination of equator to orbit: 122^o

Inclination of orbit to ecliptic: 17.1^o

Diameter: 2300 km

Diameter (Earth=1): 0.18

Mass: 1.29 x 10to22 kg

Mass (Earth=1): 0.002

Mean density: 2030 kg/m3

Surface gravity (Earth=1): 0.04

Escape speed: 1.1 km/s

Mean surface temperature: -223 ^oC= -369 ^oF=50 K