Ch. 6 - Astronomical Instruments (Telescopes)

Why do we need telescopes? Humans can only see 6000 stars at night and cannot resolve (discern) the detail of objects in the sky if they are too close together. Humans also cannot see anything but visible light. We also need some way to record images, like in photography.

A Reflecting Mirror brings light to a focus

A Refracting Lens can form an image by using the principle of the refraction of light

Image Formation can occur with a concave mirror

Two types of Telescope: Reflectors and Refractors

Types of Reflecting Telescopes

The Palomar Telescope was the largest for many years

Palomar Telescope (notice the person near the focus)

exposure time of the photo is obviously limited. Telescopes should be large to give lots of sensitivity to dim light by collecting a large area of light. Longer exposures also produce better images. But you have to quit before dawn, so the exposure time of the photo is obviously limited.

Mauna Kea Observatory in Hawaii

Resolution is critical for seeing image detail

Diffraction is an effect that limits resolution in images Diffraction is an effect that limits resolution in images. Large openings (apertures) reduce this spreading effect.

Atmospheric Turbulence is reduced at high altitudes

The Hubble Space Telescope is above the atmosphere.

Hubble Space Telescope images are much better than from ground-based telescopes of the same size.

Telescopes are available for most of the Electromagnetic Spectrum Radio (and microwave), infrared, visible, ultraviolet, X-ray, Gamma ray

The radio telescope at Green Bank, West Virginia can operate day and night.

The Arecibo Observatory (Puerto Rico) is a large radio telescope.

A radio “image” of a Radio Galaxy, along with the visible image

The Very Large Array Interferometer near Socorro, New Mexico, uses an array connected by electronics

Comparison of radio image (left) and optical image (right)

Infrared Telescopes are hoisted by balloons or put in orbit to get above the water vapor in the atmosphere.

Infrared Image of the constellation Orion, compared to the visible image on the right

The Hubble Space Telescope can obtain ultraviolet pictures The Hubble Space Telescope can obtain ultraviolet pictures. Ultraviolet images are shown using false color.

X-ray Telescopes are made of mirrors of special layered metal and are put in orbit because X-rays do not penetrate far in air.

Chandra Observatory, mounted in the shuttle Columbia

The Compton Gamma Ray Observatory, during deployment from the space shuttle

A Gamma-ray image does not show the detail of visible images, but indicates very energetic phenomena.

Multiple Wavelengths give us a fuller picture of the cosmos