Telescopes

Galileo Galilei (1564-1642)

History invented by Dutch lens maker in early 1600’s. Galileo: small 30X scope Observed the moon and “began” the modern age of Astronomy where measurement was more important than philosophy

How a telescope works gathers light through the objective (mirror or lens) wider is better because it gathers more light ability to see faint objects increases proportionally with the square of the radius of the objective focuses light viewed through an eyepiece (changing the eyepiece changes the magnification)

Major Telescope Parts Eyepieces Tripod & Mount Tube Assembly Focuser

General types of telescopes Refracting (objective is a lens) Reflecting (objective is a mirror) Newtonian (reflects once before hitting eyepiece) Cassegrain (reflects twice beefore hiting eyepiece)

Refractors (glass lens)

Refractors

Advantages and Disadvantages Easy to use and reliable High contrast images with no secondary mirror or diagonal obstruction. Sealed optical tube reduces image degrading air currents and protects optics. More expensive per inch of aperture Heavier, longer and bulkier than equivalent aperture reflectors. Small apertures Less suited for viewing small and faint deep sky objects. Color changes due to colors of light bending different amounts.

Reflectors (mirror)

Cassegrain reflector

Reflectors

Advantages and disadvantages Lower cost per inch of aperture Reasonably compact and portable up to focal lengths of 1000mm. Excellent for faint deep sky objects such as remote galaxies, nebulae and star clusters. Reasonably good for lunar and planetary work. Open optical tube design allows image-degrading air currents and air contaminants More fragile Large apertures (over 8") are bulky, heavy and tend to be expensive.

Catadioptric telescopes Best all-around, all-purpose telescope design. Combines the optical advantages of both lenses and mirrors while canceling their disadvantages. Sharp images over a wide field. Very good for lunar, planetary and binary star observing or photography. Closed tube design reduces image degrading air currents. Most are extremely compact and portable. Large apertures at reasonable prices and less expensive than equivalent aperture refractors.

Catadioptric Telescopes

Problems with earth-based telescopes Earth’s atmosphere reflects certain wavelengths x-rays, gamma rays and most UV light is not transmitted by our atmosphere Earth’s atmosphere blurs images the bending of light by the atmosphere depends on the temperature of the “air” “twinkling” (shimmering) effect “Light pollution” Solution? Put the telescope in space.

Gray = amount transparant

Disadvantages of space-based telescopes Expensive to launch and maintain Difficult to repair Low lifetime

Examples of space-based telescopes Hubble Space Telescope 3 times better resolution can see fainter objects Chandra X-ray Observatory Compton Gamma-Ray Observatory