August 2015

Financials:

Beginning balance June 1--$1829.67

One family joined in June—2 adults, 1 child

Paid Astronomical League dues $180.00

Filed tax exempt status forms for U.S. and Oklahoma governments

Ending balance June 30 $1689.67

No new members in July

34 people at tonight’s meeting—a new record? Several sets of visitors!

Virgil’s astronomy report:

The name of the comet the Philae lander touched down on is Churyumov-Gerasimenko or “Chury” for short

Minor planet Ceres has a small atmosphere

New planet discovered 21 light years away

Pluto: flowing nitrogen ice on Pluto is similar-looking to glaciers on Earth

New telescope is being built in China

Telescope Basics, hosted by Evan Zorn

Historical background:

Galileo was the first person to view the heavens using a telescope in a systematic fashion. He was the first person to see the 4 major moons of Jupiter. He used a reflector telescope, a type of scope that bends the light to focus light toward the back of the telescope.

The problem with a reflector-type telescope is its chromatic aberration. Colors of wavelengths are slightly different so the focus is in a slightly different plane for each color.

This causes “color ringing”.

All telescopes used up to the time of Isaac Newton are reflector types.

Isaac Newton tried to remove the effects of the chromatic aberration. If you use a mirror, there is no chromatic effect. Such telescopes are also cheaper to make because the only precise surface is the mirror. Telescopes with a primary and secondary mirror are known as “Newtonian Reflectors”.

The Hubble telescope as well as most other telescopes are reflector telescopes.

Laurent Cassegrain (1629-1693), a Catholic priest, developed the Cassegrain telescope in 1672. His improvement to the reflector telescope was having the light path go through a hole in the primary mirror.

Bernhard Schmidt invented the Schmidt camera in 1930 which then led to the Schmidt-Cassegrain telescope. This type of telescope has an aspherical corrector plate which corrects the coma and astigmatism.

John Dobson who developed the relatively simple Dobson telescope was born in China, then moved to San Franscisco. He joined the Vedanta Society monastery in San Francisco, becoming a monk of the Ramakrishna Order. He became involved with telescope design after joining the order but eventually his telescope work led to his removal from the order. After leaving the order he co-founded the San Francisco Sidewalk Astronomers. He died last year at the age of 98.

Daryl Doughty’s presentation on his own Schmidt-Cassegrain type telescope:

There are 2 basic telescope coordinate systems, the azimuth and the horizontal axis. Azimuth is expressed in terms of N (0 or 360 degrees), South (180 degrees), East (90 degrees) and West (270 degrees). The horizontal axis for his scope is 62 degrees altitude or elevation. You use these two measuresments like you use latitude and longitude. He can pivot his telescope in any direction along the vertical axis (azimuth). For example, he can tilt it to be parallel to the earth’s axis of rotation.

He uses a German equatorial mount with 2 perpendicular axes of rotation. This type of mount needs a counterweight to balance the telescope; need motors running on both axes. This type of mount wouldn’t work well close to the equator or the North Pole.

His advice in buying a telescope: get one with a good mount that is stable, steady and big enough to handle the telescope that you buy. He built his own observatory in his back yard with his permanent German equatorial style mount.

John Grismore’s presentation on his own telescope:

He has a portable “GoTo” computerized telescope, a Celestron 6-inch Schmidt-Cassegrain. It has an Ioptron computerized mount with celestial objects pre-loaded into it. It can calculate the coordinates of an object once it knows altitude, azimuth and time of day. Its axis retracts back into the mount. The top of his telescope has a GPS unit that shows latitude, longitude and time of day. It has “home” and “park” positions North/South. Use a level with this telescope to make sure it is pointing up. You select an object you wish to view and then “slew” to it. You can put a VSLR camera on the scope to take pictures. This type of telescope is not recommended for a beginner. It is helpful if you are familiar with the sky and telescope alignment first. The telescope, when used, must be fairly level and point fairly close to the south. It can take time to get it to level. John’s scope cost about $900. A fancier scope would cost about $1200 and a more basic one $300-400.

Azimuth mounts in general don’t rotate images. You can only photograph 90 second-two minute intervals before get rotational effects.

Steve Plank’s presentation on his own telescopes:

Steve showed us two telescopes. One is a Vixen MC110L which is a modified Cassegrain scope. It doesn’t have a corrector plate but otherwise internally it is like a Cassegrain; a type of reflector scope. Steve said this is probably the best beginner scope you can buy, in his opinion. It is sturdy and rugged. You can turn it vertically or horizontally. You can buy a mount and scope together for about $500-550.

If you try to look at the sun (with any kind of telescope) need a solar filter made specially for that scope.

The second type of telescope he showed us was a 10-inch zoom lens Dobson. It has a two-inch focuser with 2 speeds. Cost $499 with everything but the Tel-Ray. This type of telescope is good for viewing globular clusters and nebulae. You can get a 4-inch, 6-inch, 8, 12, and 16-inch Dobson. The difference between a 4-inch, 6-inch etc. scope is how much light it gathers. The more inches, the more light. A 10-inch scope will get you more detail on Saturn, for example, but the image of Saturn itself will not be bigger than on a 4-inch or 6-inch scope.

Steve recommends also to come to a club Star Party before buying a scope. We might have one in the fall at Tri County Tech. You can also look at telescopes.com

December presentation on lunar observation?