The Very Large Array (VLA) in New Mexico

Observations at wavelengths other than visible light are revealing previously invisible sights Visible light imageradio 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 Ordinary visible infrared Map of Orion region

Consider Orion as Seen in Different Wavelengths of Light!

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

Yesterday’s 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!

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 1.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 1. Angular Resolution smallest angle which can be seen  = 1.22 / D 2. Light-Collecting Area The telescope is a “photon bucket” A =  (D/2) 2 A D

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 –focuses light using lenses Reflector –focuses light using mirrors –used exclusively in professional astronomy today

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

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

Refracting telescopes have drawbacks Spherical aberration Chromatic aberration Sagging due to gravity distorting the lens Unwanted refractions opaque to certain wavelengths of light

Refractor Yerkes 40-inch telescope; largest refractor in the world

Reflector Gemini 8-m Telescope, Mauna Kea, Hawaii

Reflectors MMT – Mt. Hopkins, AZ SUBARU – Mauna Kea, HI

Reflecting telescopes use mirrors to concentrate incoming starlight

Newtonian Focus Prime Focus Cassegrain focus coude’ focus

Astronomer’s face two major obstacles in observing the skies Light Pollution from Cities

Tucson, Arizona in 1959 and 1980

Astronomer’s face two major obstacles in observing the skies Light Pollution from Cities Effects of Twinkling from Earth’s atmosphere

Rapid changes in the density of Earth’s atmosphere cause passing starlight to quickly change direction, making stars appear to twinkle.

Irregularities in the atmosphere’s density cause the light to not arrive at the telescope as plane parallel waves. Lens Atmosphere

Haleakalä Observatory, Maui (Faulkes Telescope North)

Advanced technology is spawning a new generation of equipment to view the universe CCDs (charge-coupled devices) Large telescopes on remote mountain tops –Maunakea –Cerro Pachon in Chile Orbiting space observatories Adaptive Optics to counteract the blurring of Earth’s atmosphere

Adaptive Optics (AO) It is possible to “de-twinkle” a star. The wavefronts of a star’s light rays are deformed by the atmosphere. By monitoring the distortions of the light from a nearby bright star (or a laser): –a computer can deform the secondary mirror in the opposite way. –the wavefronts, when reflected, are restored to their original state. AO mirror offAO mirror on Angular resolution improves. These two stars are separated by 0.38  Without AO, we see only one star.

A.O. Movie…

Instruments in the Focal Plane 1. Imaging –use a camera to take pictures (images) –Photometry  measure total amount of light from an object 2.Spectroscopy –use a spectrograph to separate the light into its different wavelengths (colors) How do astronomers use the light collected by a telescope?

Imaging Filters are placed in front of a camera to allow only certain colors to be imaged Single color images are superimposed to form true color images.

A little color theory:

So why do TV’s use RGB? Shouldn’t they use RYB? Shouldn’t they use RYB?

Spectroscopy The spectrograph reflects light off a grating: a finely ruled, smooth surface. Light interferes with itself and disperses into colors. This spectrum is recorded by a CCD detector.