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1. Astronomers Observe Light Radiated Toward Earth By Matter in Space

2. Light is Energy That is Radiated as a Wave with both Electric and Magnetic Properties

3. The Electromagnetic Spectrum Shows All Light Grouped in BANDS organized by wavelength

All light travels through space at the same speed -- The Speed of Light -- 300,000 kilometer/second !!!

The distance light travels in one year is called a Light Year -- about 10 trillion kilometers

Our galaxy -- the Milky Way -- is about 100,000 light years in diameter and contains more than 200 billion stars!!

The nearest star system to our Sun is Alpha Centauri -- about 4.2 light years away!! How many kilometers is that??

Optical Window – some UV light, all visible light and some infrared light

Radio Window – some radio waves and some microwaves

Fortunately, gamma rays, x-rays and much UV light are absorbed by Earth's atmosphere -- sparing us from harm

Earth's atmosphere is transparent (like a window) only to certain bands, including:

Galileo Improved the Refracting Telescope to observe visible light

Refractors use curved glass lenses to magnify objects up to 30x

Visible light is refracted (bent) as it enters and exits a curved glass lens

-- visible light is refracted (bent) as it passes from air into material of a different density.

-- white light bent by glass prism is spread into rainbow

-- through water too!

You can blend colors back into white light too!

-- Lenses can be arranged to refract (bend) light in ways that make objects appear larger than they are.

-- The lens tricks the brain into thinking the object is larger than it is

-- Object is magnified

Convex Glass Lens

Chromatic Aberration is a problem with refracting lenses

-- white light is separated into colors of the rainbow

-- creates image blurry with rainbows at edges

Diagram of Refracting Telescope

Sir Isaac Newton developed Reflecting lens Telescopes

Reflector Telescopes use mirrors (instead of glass lenses)

Two Advantages of reflecting telescopes:

1. No Chromatic Aberration – no separation of white light into colors of the rainbow

2. Mirrors weigh less than glass lensesUniversal Law of Gravitation

All objects in the universe exert a force on each other that is related to the mass of the two objects and the distance between them

This force is gravity

Reflecting Telescope uses mirrors to gather and focus light

Mirrors focus light by reflecting it, NOT refracting it

Modern Telescopes Are Designed to Observe Specific Bands of Light

Arecibo Radio Telescope in Puerto Rico – located on a mountain and dug into the ground facing up so that it only detects radio waves from space, not radio waves emitted by radio stations. Radio waves are very long, so receiver must be very wide and it does NOT have to be a smooth surface

Since our atmosphere is transparent to Radio Waves we can position radio telescopes on Earth

Arecibo also emits radio waves that bounce off near-Earth asteriods and back to the telescope so we can keep track of how close they come to Earth!

Click here to see a radio image of an asteroid taken by the Arecibo radio telescope

The South Pole Telescope observes microwave light from space. It is located in Antarctica because the altitude is very high and the air is very dry. The atmosphere on mountain tops is much thinner and thus is more transparent to microwaves. Moisture in the air is a very effective blocker of microwaves.

Image of the “Cosmic Microwave Background” energy left over from the formation of the Universe 13.75 billion years ago – aka, the “Big Bang”

Spitzer Space Telescope – designed to detect the infrared light emitted by the cooler gas of Nebulas (the remains of supernovae) and the rings of Jupiter, Saturn, Uranus and Neptune

Earth's atmosphere absorbs most infrared light, so infrared telescopes are designed to orbit Earth above the atmosphere

Image of Saturn’s largest ring – made by Spitzer

Hubble Space Telescope has orbited above Earth’s atmosphere for over 20 years – taking pictures of the visible light emitted and reflected by objects in space

Although our atmosphere is transparent to visible light, Hubble takes much clearer pictures because it is above the atmosphere

Hubble Ultra Deep Field of the many Galaxies in our region of the Universe

SOHO Solar Space Telescope – detects UV light emitted by the Sun

SOHO helps astronomers predict dangerous "space weather" caused by massive ejections of particles and energy by the Sun.

Space weather can cause satellites to fall out or orbit, expose airline passengers to be exposed to high doses of radiation and cause electrical blackouts on Earth.

Image of the UV light emitted by the Sun taken by the SOHO space telescope, showing a large ejection of energy and particles in the upper right quadrant of the Sun.

Image is colorized to help us see different wavelengths within the band of UV light

Chandra Space Telescope

Designed to detect X-rays emitted by the hottest objects in space such as neutron stars and black holes

All space X-rays are blocked by our atmosphere

Infrared image of the famous “Crab Nebula” taken by the Spitzer Space telescope. It shows the cooler dust swirling around the remains of an exploded star

Image of the same “Crab Nebula” taken by the Chandra X-ray telescope. The central white star spewing a jet of x-rays is clearly visible

Hubble Space Telescope Video