1. 6-1 Radiation: Information from Space
Light and Telescopes
6-1 Radiation: Information from Space

2. Light as a Wave and a Particle
Electromagnetic radiation – changing electric and magnetic fields that travel through space and transfer energy from place to another
Ex. Light or radio waves
Moves at the speed of light (186,000 mi/sec)

3. Light as a Wave and a Particle
Electromagnetic radiation is a wave phenomenon so we use the common measurements of wavelength and frequency
Wavelength is the distance between successive peaks of a wave
Frequency is the number of cycles that pass in one second

4. Light as a Wave and a Particle
An easy way to remember the relationship between wavelength and frequency is the larger (higher) the frequency the smaller (shorter) the wavelength and vise versa.

5. Light as a Wave and a Particle
Couple other terms dealing with light of importance:
Photon is a particle of light
Nanometer (nm) is the unit used to measure light particles
This is used because the wavelength of light particles are so much smaller (shorter) than other waves measured

6. Electromagnetic Spectrum
This spectrum is used to classify electromagnetic radiation
We are most familiar with the spectrum of visible light
Light near the short-wavelength end of the visible spectrum (400 nm) looks violet to our eyes, and light near the long-wavelength end (700 nm) looks red
Most electromagnetic radiation is absorbed in Earth’s atmosphere, and only radiation in the visual window and the radio window can reach Earth’s surface
Pg 101 Figure 6-2

7. Electromagnetic Spectrum
MAKE SURE YOU KNOW SPECTRUM ORDER FOR TEST…MULTIPLE QUESTIONS

8. 6-2 Astronomical Telescopes
Light and Telescopes
6-2 Astronomical Telescopes

9. Refracting Telescopes
The main element in a refracting telescope is a lens, a piece of glass carefully shaped so that light striking it is refracted, or bent, into an image

10. Refracting Telescopes
Terms:
Focal length is the distance from a lens to the point where it focuses parallel rays of light
Objective lens is the long-focal-length lens that forms an image of the object viewed
This lens is closest to the object
Eyepiece is a short-focal-length lens used to enlarge the image in a telescope
This lens is nearest the eye of the observer

11. Refracting Telescopes
Positives of Refracting Telescopes:
They are great for viewing planets, the moon, and star clusters
Negatives of Refracting Telescopes:
They are not very good for viewing very faint objects such as galaxies
REFRACTING ANIMATION

12. Reflecting Telescopes
In a reflecting telescope, a concave mirror, the objective mirror, focuses the starlight into an image that can be viewed with an eyepiece

13. Reflecting Telescopes
Positives for Reflecting Telescopes:
They are great for viewing faint objects such as galaxies. Very affordable.
Negatives for Reflecting Telescopes:
They are larger and this often makes them more difficult to store. They also need to be maintained often to make sure the optics are properly aligned.
REFLECTING ANIMATION

14. The Powers of a Telescope
A telescope can aid our eyes in only three ways
These three ways are the three powers of a telescope
They make images brighter, more detailed, and larger

15. The Powers of a Telescope
Light-gathering power refers to the ability of a telescope to collect light
Catching light in a telescope is like catching rain in a bucket – the bigger the bucket, the more rain it catches
Light-gathering Power = (DA/DB)2
For example, suppose we compare a telescope 24 cm in diameter with a telescope with a 4 cm diameter. The ratio of the diameters is 24/4, or 6, but the larger telescope doesn’t gather 6 times as much light. Light-gathering power increases as the ratio of diameters squared (in this case 62 or 6x6), so it gathers 36 times more light than the smaller telescope.

16. The Powers of a Telescope
Resolving Power is the 2nd power and it refers to the ability of a telescope to reveal fine detail
Resolving Power = 11.6 D
For example, the resolving power of a 25-cm telescope is 11.6 divided by 25. This means the resolving power is .46

17. The Powers of a Telescope
The third and least important power of a telescope is magnifying power, the ability to make the image bigger
Magnifying power = Focal length of the objective lens
Focal length of eyepiece
For example, if a telescope has an objective with a focal length of 80 cm and we use an eyepiece whose focal length is 0.5 cm, the magnification is 80/0.5 which gives us a magnification power of 160 times

18. The Powers of a Telescope
The search for light-gathering power and high resolution explains why almost all major observatories are located far from major cities and usually on high mountains
Astronomers avoid cities because of light pollution
This is the phenomenon of the brightening of the night sky by light scattered from artificial outdoor lighting, which can make it difficult or impossible to see faint objects like stars in the sky

19. Picture above is showing amount of light created at night by cities
Picture above is showing amount of light created at night by cities
Picture to right is showing the glare these lights put into the sky

20. Light and Telescopes
6-3 Special Instruments

21. Imaging Systems
Most modern astronomers use charge- coupled devices (CCDs) to record images
These devices can be used like a small photographic plate
They can detect both bright and faint objects in a single exposure, are much more sensitive that a photographic plate, and can be read directly into computer memory for later analysis

22. The Spectrograph
Spectrograph is a device that separates light by wavelength to produce a spectrum
Sir Isaac Newton was one of the first people to understand the changing of color of sunlight after it passes through a prism – he then concluded that white light was made up of a mixture of all colors

23. Light and Telescopes
6-4 Radio Telescopes

24. Operation of a Radio Telescope
A radio telescope usually consists of four parts:
A dish reflector, an antenna, an amplifier, and a recorder
These components, working together, make it possible for astronomers to detect radio radiation from celestial objects
This page was copied from Nick Strobel's Astronomy Notes. Go to his site at for the updated and corrected version.

25. This page was copied from Nick Strobel's Astronomy Notes
This page was copied from Nick Strobel's Astronomy Notes. Go to his site at for the updated and corrected version.
The Robert C Byrd Green Bank Telescope is the largest fully steerable radio telescope in the world

26. Limitations of the Radio Telescope
A radio astronomer works under three handicaps
Poor resolution
As with an optical telescope the only way to help improve these handicaps is to build a bigger telescope – which is the reason that radio telescopes are so large
To help improve resolution, radio astronomers can combine two or more telescopes

27. Limitations of the Radio Telescope
Low resolution
To help combat low resolution radio astronomers must build large collecting dishes
Interference
To avoid this kind of interference, radio astronomers locate their telescopes as far from civilization as possible
Keep them hidden deep in mountain valleys, they are able to listen to the sky protected from human-made radio noise

28. Advantages of Radio Telescopes
Three factors make Radio Telescopes worth while
First, and most important, a radio telescope can show us where clouds of cool hydrogen are located between stars
Radio signals have relatively long wavelengths, they can penetrate the vast clouds of dust that obscure our view at visual wavelengths
A radio telescope can detect objects that are more luminous at radio wavelengths than at visible wavelengths. This includes everything from the coldest clouds of gas to the hottest stars