 From the ground the atmosphere distorts images.  Light pollution from streetlights, city lights, car lights, and more hinders the seeing conditions through a telescope.  On the surface, the best place to look at stars is on a very high altitude where the atmosphere is clearer.  If you can see stars twinkling, conditions are relatively good for optical viewing.

Solutions: Put telescopes on mountaintops, especially in deserts Put telescopes in space

 Telescopes are designed to collect as much light as possible from a light sources and deliver it to a detector so we can study it more.  3 types of optical scopes-  Reflectors  Refractors  Cassegrain

 Refractors go through a lens.  The lens bends light as is goes from travelling through air to glass.  This makes a distorted image.  Benefits:.

 Virtually maintenance free due to their close optical tube design  No mirror to adjust  Rugged and long-lasting design  Great as a daytime telescope also for birding and other hobbies vs. other telescopes  Generally lighter and smaller optical tube assembly (OTA) per inch of aperture

 Most expensive per inch of aperture than other telescopes  Price of refractors escalates highly after 3 inches  Affordable refractors are very small aperture which will be outgrown by many astronomers over time  Image gets distorted when bent through the lens

 Easy to use and even construct  Excellent for faint deep sky objects such as remote galaxies, nebulae and star clusters because of their larger apertures for light gathering.  Delivers very bright images  Reasonably compact and portable  A reflector costs the least per inch of aperture compared to refractors since mirrors can be produced at less cost than lenses

 Slight light loss due to secondary obstruction when compared with refractors  The tube is open to the air, which means dust on the optics even if the tube is kept under wraps  Reflectors may require a little more care and maintenance

Reflecting mirror Light is collected on a main mirror, that reflects it to the prime focus which then leads to our eyes.

Most versatile type of telescope Best near focus capability of any type telescope First-rate for deep sky observing or astrophotography with fast films or CCD's Excellent for lunar, planetary and binary star observing plus terrestrial viewing and photography Closed tube design reduces image degrading from air currents Compact and durable

 More expensive than reflectors of equal aperture  Its appearance may not be popular with everybody's taste  Slight light loss due to secondary mirror obstruction compared to refractors

The prime focus of the telescope is where the incoming light is focused and sent to our eyes

The Keck telescope on top of Mauna Loa in Hawaii, a modern research telescope:

Effect of improving resolution: (a) 10′; (b) 1′; (c) 5″; (d) 1″

Image processing by computers can sharpen images

Radio telescopes: Similar to optical reflecting telescopes Prime focus Less sensitive to imperfections (due to longer wavelength); can be made very large

Largest radio telescope: 300-m dish at Arecibo

Advantages of radio astronomy: Can observe 24 hours a day Atmospheric conditions don’t interfere- can be cloudy and rainy Observations at an entirely different frequency; get totally different information

Interferometry: Combine information from several widely spread radio telescopes as if they came from a single dish Resolution will be that of dish whose diameter = largest separation between dishes

Interferometry involves combining signals from two receivers; the amount of interference depends on the direction of the signal

Can get radio images whose resolution is close to optical Interferometry can also be done with visible light but is much more difficult due to shorter wavelengths

Infrared radiation can image where visible radiation is blocked; generally can use optical telescope mirrors and lenses

Infrared telescopes can also be in space; the image on the left is from the Infrared Astronomy Satellite

The Spitzer Space Telescope, an infrared telescope, is in orbit around the Sun. These are some of its images.

Ultraviolet observing must be done in space, as the atmosphere absorbs almost all ultraviolet rays.

X-rays and gamma rays will not reflect off mirrors as other wavelengths do; need new techniques X-rays will reflect at a very shallow angle and can therefore be focused

X-ray image of supernova remnant

Gamma rays cannot be focused at all; images are therefore coarse

Much can be learned from observing the same astronomical object at many wavelengths. Here, the Milky Way: