Homework #4 What is the maximum resolution of your eyes (assume the wavelength range that your eyes are sensitive to is 300 – 700 nm and that your iris is ½ cm in diameter. What size eye would be required to see in the radio with the same maximum resolution of your eyes? (use 21 cm for the wavelength of typical radio waves) What is the maximum resolution of the VLBA (longest baseline = 5000 km) at a wavelength of 21 cm?

Telescopes

Astronomical objects emit all of these different kinds of radiation in varying amounts

Mm/Submm

Maunakea’s height

Radio wavelength observations are possible from Earth’s surface

The Very Large Array (VLA) in New Mexico

Observations at wavelengths other than visible light are revealing previously invisible sights Visible light image radio wavelength image

Astronomers use different instruments to look at light of different wavelengths - sometimes, we even have to go above Earth’s atmosphere.

SOFIA - the Stratospheric Observatory for Infrared Astronomy

Observations at other wavelengths are revealing previously invisible sights UV infrared Map of Orion region Ordinary visible

Consider Orion as Seen in Different Wavelengths of Light!

http://www. cnn. com/2001/LAW/02/20/scotus. heatdetector. 01. ap/index http://www.cnn.com/2001/LAW/02/20/scotus.heatdetector.01.ap/index.html

High above Earth’s atmosphere, the Hubble Space Telescope provides stunning details about the universe

Hubble Space Telescope Views of Orion Nebula showing stars hidden in clouds http://oposite.stsci.edu/pubinfo/pr/97/13/A.html

The Sun as seen in visible light from Earth and from space in X-rays by satellites

High Energy Gamma Rays - Compton Gamma Ray Observatory (GRO) Satellite

The Sky’s emission of Gamma Rays

But, we receive GRBs from every direction !! The fact that GRBs come from every direction imply that GRBs don’t come from our galaxy, but from other galaxies spread in every direction!

The typical refracting telescope: magnification = (objective lens focal length / eyepiece lens focal length)

Three main functions of a telescope brighten (called light gathering power) see fine detail (called resolution) and least important, magnify magnification = (objective lens focal length / eyepiece lens focal length)

A larger objective lens provides a brighter (not bigger) image

Two Fundamental Properties of a Telescope Angular Resolution smallest angle which can be seen  = 1.22  / D where  = wavelength; D = diameter of the aperture

Angular Resolution The ability to separate two objects. The angle between two objects decreases as your distance to them increases. The smallest angle at which you can distinguish two objects is your angular resolution.

Two Fundamental Properties of a Telescope Angular Resolution smallest angle which can be seen  = 1.22  / D Light-Collecting Area The telescope is a “photon bucket” A =  (D/2)2 D A

Angular Resolution:

Parts of the Human Eye pupil – allows light to enter the eye lens – focuses light to create an image retina – detects the light and generates signals which are sent to the brain A camera works in the same way where the shutter acts like the pupil and the film or CCD acts like the retina!

Lenses bend Light Focus – to bend all light waves coming from the same direction to a single point Light rays which come from different directions converge at different points to form an image.

Telescope Types Refractor Reflector focuses light using lenses focuses light using mirrors used exclusively in professional astronomy today

A refracting telescope uses a lens to concentrate incoming light Similar to a magnifying glass

Refracting telescopes have drawbacks Spherical aberration

Too spherical

Refracting telescopes have drawbacks Spherical aberration Chromatic aberration

Special achromatic compound lenses and lens coatings can often fix this aberration