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TELESCOPES. Telescope – a device that permits distant and faint objects to be viewed as if they were much brighter and closer to the observer. Typically used to observe the skies. Used to learn about A. distant stars, B. nebulas and C. galaxies. INTRODUCTION. Telescopes
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Telescope – a device that permits distant and faint objects to be viewed as if they were much brighter and closer to the observer. • Typically used to observe the skies. • Used to learn about • A. distant stars, • B. nebulas and • C. galaxies. INTRODUCTION
Telescopes • Used to tackle scientific questions about the: • a. birth of the universe, • b. emergence of structure in the early universe, • c. formation of evolution of stars, galaxies and planetary systems and • d. conditions for the emergence of life itself. Introduction
Optical telescopes – work by collecting and magnifying visible light that is given off by stars or reflected from the surface planets. Focus – a point in space where all the light rays converge. Eye piece – small magnifying lens placed at the focus allows the image to be viewed. Cameras – instruments placed near the focus make a precise recording of the light gathered by a telescope. INTRODUCTION
Objective lens - the lens or combination of lenses in an optical instrument nearest to and facing the object being viewed. Focal length - distance from lens to focal point. INTRODUCTION
Observatories – Earth based telescopes located around the world. Only radio waves, visible light and some infrared radiation can penetrate Earth’s atmosphere. • Space telescopes – can collect waves from other regions of the electromagnetic spectrum. • Spectroscopy – visible light is divided into component wavelengths through the use of prism or diffraction grating. • Decodes starlight to yield information about an object’s temperature, motion and other dynamics, chemical composition and presence of magnetic fields. INTRODUCTION
Kitt Peak National Observatory is silhouetted against the night sky. Located near Tucson, Arizona, Kitt Peak houses a variety of instruments, including a large McMath solar telescope. The telescope’s main mirror is 150 cm (59 in) in diameter and has a focal length of 91.5 m (300 ft). Kitt Peak also houses a 400-cm (157-in) reflecting telescope and a 11-m (36-ft) radio telescope. KITT PEAK NATIONAL OBSERVATORY
II. Optical Telescopes • A. Refracting telescopes or refractors – use a glass lens to bend, or refract, starlight and bring it to a focus. The convex lens bends light at the edge of the lens to a greater angle than light coming through the center so all of the rays converge to a focus. • Focal length – distance between the lens and the place where the rays converge. • Light gathering power is proportional to the size of the objective and the ratio of the focal lengths of the objective lens and the eyepiece. • Chromatic aberration – causes different colors of light to come to a different focus because every color has its own degree of refraction. • A fundamental limitation of refractors is that lenses beyond 40 inches are impractical because they weigh more than half a ton and sag under their own weight. • Cannot be supported from behind compared to optical mirrors. OPTICAL TELESCOPES
Refracting Telescope The simplest refracting telescope has two convex lenses, which are thicker in the middle than at the edges. The lens closest to the object is called the objective lens. This lens collects light from a distant source and brings it to a focus as an upside-down image within the telescope tube. The eyepiece lens forms an image that remains inverted. More complex refracting telescopes contain an additional lens to flip the image right-side up. Refracting telescope
B. Reflecting Telescopes – uses precisely curved mirror instead of a lens to collect starlight. The concave mirror brings reflected light waves to a focus at a point above the mirror. Useful for gathering light from dim objects. Galileo is considered to be the first person to use telescopes for astronomical observations. His design was capable of magnifying objects 30 times. OPTICAL TELESCOPES
The twin Keck telescopes are the world’s largest optical telescopes. They sit in the Mauna Kea Observatory on Mauna Kea, a dormant volcano in Hawaii. The Mauna Kea Observatory is located at an altitude of 4,205 m (13,796 ft), which permits excellent nighttime viewing with a minimum of interference from artificial light sources. The Keck telescopes are both reflecting telescopes that use a giant mirror consisting of 36 individual segments. The segments collect light and bring it to a common focus. On both mirrors, each of the mirror’s 36 segments measure about 2 m (6.6 ft) across.
The first reflecting telescope was designed by Sir Isaac Newton in 1668. A reflecting telescope uses a curved mirror to focus the light. Light from distant objects such as stars and galaxies enters the telescope tube in parallel rays. These rays are reflected from the concave mirror to a diagonal plane mirror. The diagonal mirror reflects the light through a hole in the side of the telescope tube to a lens in the eyepiece. REFLECTING TELESCOPES
Reflecting telescopes can be made larger than refracting telescopes because the curved mirror can be supported along its entire surface, while a large lens can only be supported at its edges. A large surface can collect more light from distant stars than a small surface. Modern reflecting telescopes include the 508-cm (200-in) reflector at the Palomar Observatory in California and the 400-cm (158-in) reflector at Cerro Tololo Inter-American Observatory near La Serena, Chile. Reflecting telescopes
> Reflecting telescope’s light sensitivity increases with the square of the diameter of the telescopes mirror. Doubling mirror’s diameter increases light-gathering power by a factor of four. > Larger optical telescopes can see faint objects better and faster. > Mirror has a hyperbolic or parabolic shape bringing light to a precise focus. It can also be a sphere. > Mirror could be made with Pyrex glass, borosilicate glass and glass-ceramic composite. > Huge mirrors are expensive and difficult to make, challenging to move while tracking celestial objects and heavy. E.g. The 200 inch Hale telescope on California’s Mount Palomar weighs 14 tons. OPTICAL TELESCOPES
Twin Keck telescopes in Mauna Kea, Hawaii broke the mirror size barrier by combining 36 hexagonal 72 inch mirror with a light collecting power equal to that of a 400 in mirror. • Mirror weight has been reduced by sandwiching a honey comb pattern of glass ribs between a thin, but rigid concave mirror and a flat back plate. • Meniscus mirrors too thin to support their own weight were developed. Adjustable framework supports the meniscus mirror. • Servomechanical actuators – controlled by the computer, continually adjust the shape of the mirror as it tracks celestial targets. OPTICAL TELESCOPES
C. Resolution – the ability to see fine detail. Increases with mirror or lens size. Turbulent atmosphere blurs incoming starlight. Adaptive optics- distorts mirrors to remove the blur of starlight. E.g. Mauna Kea outfitted with this technology takes pictures 20 times better. Can resolve a coin size at distance of more than 50 kilometers. D. Optical Interferometry – combines signals from telescopes in separate locations so that resulting image is equal to that received from one giant telescope. E.g. Very Large Telescope (VLT) in the Acatama Desert in northern Chile. > VLT combines light from four 323 inch telescopes and several smaller telescopes to produce an image equivalent to that of a 630 inch telescope. > Use to resolve bright, closely paired objects like double stars. May be used to observe Earth-size planets orbiting stars. Optical telescopes
