WHERE: AT EXPLORIT Science Center, 3141 5th Street, Davis.

ALL ABOUT TELESCOPES!
Saturday, December 4, 2004
from 7:00 - 9:00p.m. at Explorit
3141 5th Street, Davis

Join us Saturday evening, Dec. 4th, at 7:00 p.m., when we will discuss the different types of telescopes and accessories. We will also look at the stars in the night sky, weather permitting.

On a clear night far from city lights, we can see about 2000-3000 stars with our naked eyes. To see millions of stars, we need to use telescopes or binoculars. Telescopes work like our eyes-the image formed is upside-down and flipped right to left. The brain corrects the eyes' image to its right orientation. In a telescope, the image is not usually corrected.

About Telescopes
There are three basic types of telescopes. Refracting (lens) telescopes use lenses to refract or bend light to produce an image. The primary convex objective lens (at the top of the telescope) collects and focuses light on the smaller eyepiece lens (at the base). It has excellent contrast but gets expensive and bulky with large diameter lenses. Reflecting (Newtonian) telescopes use mirrors to reflect light to produce an image. Light is collected by a concave primary mirror (at the base of the telescope) and reflected back to a flat secondary mirror (near the top of the scope), and then reflected on the eyepiece lens. It has medium contrast, but is relatively inexpensive and bulky as size increases. Combo (Schmidt-Cassegrain or Maksutov-Cassegrain) telescopes 'fold' light by using a combination of mirrors and lenses to form an image. Light is collected by a concave primary mirror (at the base of the telescope) and reflected back to a flat secondary mirror and correcting lens (at the top of the scope), and then reflected on the eyepiece lens. It has a condensed, portable tube and is less expensive than a big refractor.

Telescopes are mounted on alt-azimuth or equatorial tripods that allow them to point to a specific location in the sky. Telescopes with drive motors allow the scopes to track objects as they move in the sky due to Earth's rotation A Dobsonian telescope is a Newtonian mounted on a cradle rather than a tripod.

Eyepiece lenses focus the collected light to the eye and determine the magnifica-tion, brightness and contrast of the image. Eyepieces contain 2 to 5 lens elements with single or multiple anti-reflective coatings. Plossl, Orthoscopic, Kellner, and Huygenian are examples of eyepieces. The quality of an eyepiece is determined by its make, focal length (factor in the telescope's magnifying capacity), apparent field of view (width of the field of view), and eye relief (distance between eye and eyepiece lens).

Telescopes collect starlight containing vital information such as the star's mass, velocity, chemical composition, etc. They (a) collect light coming from a star, thus making it appear brighter - Light-gathering Power (proportional to the square of the diameter of the objective lens/primary mirror), (b) bring out details - Resolving Power (equal to 5 divided by the diameter of the objective/primary), and (c) enlarge a section of the sky - Magnifying Power (equal to the focal length of the eyepiece divided by the focal length of the objective/primary). The actual field of view is equal to the apparent field of view of the eyepiece divided by the telescope's magnification. The f-number of the telescope is equal to the focal length of the objective or primary divided by its diameter.

The Winter Night Sky
Saturn (-0.0, Gemini) rises in the even-ing, Jupiter (-1.6, Virgo) rises late at night, Venus (-3.9, Virgo/Libra) & Mars (+1.7, Virgo/Libra) rise before dawn.
See Comet Machholz (Taurus) in the evening sky. Winter Solstice is Dec. 21.
Perihelion (Earth closest to Sun) is Jan. 1.
Moon's phases: Full Moon: Nov. 26/
Dec. 26, Last Quarter: Dec. 4/Jan. 3. New Moon: Dec. 11/Jan. 10, First Quarter: Dec. 18/Jan. 16.

To Receive These Bulletins via E-mail Contact Explorit at: Explorit Science Center

The Astronomy Club is for everyone - adults, children, knowledgeable or ignorant. Come to listen, look and learn, or to share your expertise or experience.