Telescopes

• Collect more light than eye

• More detailed images than human eye

• Larger aperture is better– Aperture refers to the diameter of the primary

lens or mirror of telescope

• Magnification is useless without:sensitivity and resolution are crucial

Refractor Telescope

Reflector Telescope

Reflectors

Sensitivity

Compound Mirror:

Diffraction Pattern

Angular Resolution

• Larger aperture (diameter) telescopes have smaller diffraction patterns

• The smaller the diffraction patterns result in better angular resolution (more detail)

• Diffraction limit in arcseconds = 2.5 105 (/D) = wavelength D = aperture

• Smallest detail that can be resolved

Bigger is Better

1. Better sensitivity: more light gathering area

2. Better angular resolution in most instances: more detail

Figure shows effect of larger aperture

Seeing: Atmospheric Effect

Why Put a Telescope in Orbit?

• The only reason to put a visible light telescope in space is to improve resolution!

• a) ground-based b) damaged Hubblec) enhanced image d) repaired Hubble

Atmospheric Windows

• Certain wavelengths require orbiting telescopes• Radio and visible light can be done from ground

Mauna Kea