AY Honors/Lighthouses - Advanced/Answer Key

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1. Have the Lighthouses Honor

For tips and instruction see Lighthouses.

2. Make a scrapbook including the following:
a. Pictures, post cards or drawings of twenty-five lighthouses. Label should included a brief description of: location, year built, active/non-active status, and order of the lens.
b. Write up a short history of the above lighthouses.
c. Include drawings/pictures and answers to all the requirements for this honor in your scrapbook.

2a) Pictures, post cards or drawings of twenty-five lighthouses. Label should included a brief description of: location, year built, active/non-active status, and order of the lens.

  • Collect pictures/postcards/drawings of twenty-five (25) lighthouses

2b) Write up a short history of the above lighthouses.

  • Include a write-up on the lighthouse(s) with your picture/post card/drawing

2c) Include drawings/pictures and answers to all the requirements for this honor in your scrapbook.

  • You might be able to also work (or extend) your Scrapbooking honor

3. List the development of a Fresnel lens, including:
a. Name of the gentleman that invented it.
b. Country that he came from
c. Year developed

Augustin-Jean Fresnel

3a) Name of the gentleman that invented it: Augustin-Jean Fresnel (pronounced fray-NELL) is most often given credit for the development of this lens for use in lighthouses.

3b) Country that he came from: Fresnel (May 10, 1788 – July 14, 1827), was a French physicist who contributed significantly to the establishment of the theory of wave optics.

3c) Year developed: According to Smithsonian, the first Fresnel lens was used in 1822 in a lighthouse on the Gironde River in France, Cardovan Tower; its light could be seen from more than 20 miles out.

  • A Fresnel lens is a type of lens invented by French physicist Augustin-Jean Fresnel. Originally developed for lighthouses, the design enables the construction of lenses of large aperture and short focal length without the weight and volume of material which would be required in conventional lens design. Compared to earlier lenses, the Fresnel lens is much thinner, and passes more light which allows lighthouses to be visible over much longer distances.
Cardouan Tower
  • The idea of creating a thinner, lighter lens by making it with separate sections mounted in a frame is often attributed to Georges-Louis Leclerc, Comte de Buffon. However, it is difficult to find any other sources that link Buffon to work with optics. French physicist and engineer Augustin-Jean Fresnel is most often given credit for the development of this lens for use in lighthouses. According to Smithsonian, the first Fresnel lens was used in 1822 in a lighthouse on the Gironde River in France, Cardovan Tower; its light could be seen from more than 20 miles out. Scottish physicist Sir David Brewster is credited with convincing The United Kingdom to use these lenses in their lighthouses.
  • The Fresnel lens reduces the amount of material required compared to a conventional spherical lens by breaking the lens into a set of concentric annular sections known as Fresnel zones.
  • In the first (and largest) variations of the lens, each of these zones was a different prism. Though a lens might look like a single piece of glass, closer examination reveals that it is many small pieces. It was not until modern computer-controlled milling equipment (CNC) could turn out large complex pieces that these lenses were single pieces of glass.
  • For each of these zones, the overall thickness of the lens is decreased, effectively chopping the continuous surface of a standard lens into a set of surfaces of the same curvature, with discontinuities between them. This allows a substantial reduction in thickness (and thus weight and volume of material) of the lens, at the expense of reducing the imaging quality of the lens.


4. Draw a Fresnel lens:

a. Show how prisms are used to concentrate light
b. Draw a bull’s eye lens and state its purpose

1: Cross section of a Fresnel lens 2: Cross section of a conventional plano-convex lens of equivalent power
A triangular prism, bending light
How the prisms and lens work together on the Fresnel to bend and concentrate light


5. Make a chart showing each class of Fresnel lens:

You can get a nice diagram/chart at the Library of Congress.

a. Define order and list by size

  • 1st Order - focal length 920mm. Use: Largest seacoast lights.
  • 2nd Order - focal length 750mm. Use: Great Lakes lighthouses, seacoast islands, sounds.
  • 3rd Order - focal length 500mm. Use: Seacoast, sounds, river entry, bays, channels, range lights.
  • 4th Order - focal length 250mm. Use: Shoals, reefs, harbor lights, islands in rivers and harbors.
  • 5th Order - focal length 182.5mm. Use: Breakwaters, river lights, channels, small islands in sounds.
  • 6th Order - focal length 150mm. Use: Pier or breakwater lights in harbors.

b. Name at least one lighthouse using each order


Here's a listing of the classical Fresnel Lenses in the United States: http://uslhs.org/resources_lighthouse_lenses_4.php

6. Research and describe the history of the mechanism for rotating lights

In early years and the lenses were rotated by a weight driven clockwork assembly wound by lighthouse keepers (sometimes as often as every two hours). The lens assembly usually floated in mercury to reduce friction. In more modern lighthouses, electric lights and motor drives were used, generally powered by diesel electric generators. These also supplied electricity for the lighthouse keepers.

7. Make a chart of six lighthouses showing nighttime (light) and daytime (daymark) signature.

Daymark

Lighthouses have distinguishing daymarks. No two lighthouses are exactly alike. This way, ships and sailors can determine their location. For example, if you see a red lantern and black and white spiral stripes, you will know that you are off the coast of St. Augustine.


  • Alcatraz Island Lighthouse
    Natural color with black lantern with Octagonal/Pyramidal tower.

  • Point Loma Light
    Square Pyramidal (skeletal).

  • Fourteen Foot Bank Light
    Cast Iron (Square)

  • Alligator Reef Light
    White octagonal pyramid on black skeleton tower.

  • St. Augustine Light
    Conical tower, red lantern and black and white spiral stripes

  • Thomas Point Shoal Light
    Square on hexagonal house, White with Red Roof and Black Lantern.

  • Holland Harbor Light
    Wood, Square, Red.

  • Cape Hatteras Light
    Conical, white and black spiral bands with red brick base.

Nightmark

In similar fashion, the signature or pattern of light at night is the nightmark. By viewing this distinctive signature, sailors can tell their location even in the dark.

  • Pigeon Point Light Station: Flashing white 10s
  • Point Bonita Lighthouse: Occulting white once every 4s
  • Ponce de Leon Inlet Light: fixed light (original)
  • Cape Hatteras Light: Short flash every 7.5 seconds
  • Au Sable Light: Flashing white every 6 s
  • Fort Washington Light: flashing red

8. What is a lightship? Why and where are lightships needed?

Ambrose Lightship

A lightship is a lighthouse on a ship. It allows a lighthouse to be put where a lighthouse cannot be built. For example, a lightship may be moored over treacherous reefs, or marking the narrow approaches to a channel. Also, at harbor entrance(s) where lighthouses can not be built or placed in areas too far offshore for a land-based lighthouse's lens to reach.

Here's a link for more information: http://www.nps.gov/history/maritime/ltshipmain.htm


9. Read about lighthouse keepers and list some of the hazards they faced in completing their duties.

A lighthouse keeper is the person responsible for tending and caring for a lighthouse, particularly the light and lens in the days when oil lamps and clockwork mechanisms where used. Keepers were needed to trim the wicks, replenish fuel, wind clockworks and perform maintenance tasks such as cleaning lenses and windows.

Many lighthouse keepers lived in isolated locations. The isolation could cause mental health issues. In a medical emergency they could be far from help. They had to climb towers and could fall. They also served as first responders to shipwrecks in storms which could be dangerous. Traveling over the ocean to and from work also had its hazards.

10. Study quotes by Ellen White mentioning lighthouses and discuss the meaning. Place a copy of the quotes in your scrapbook.

Here's a link to a quote: http://www.whiteestate.org/issues/Drama.html. See pages 6, 17, 18.

Whiteestate.org has a searchable database of Ellen White's writings. Type in lighthouse and see what you find.

11. Obtain a “Lighthouse Passport” and have it stamped at 10 different lighthouse locations.

12. Build a lighthouse modeled after a real lighthouse using a lighthouse kit, wood, or other medium. Know the name, location, and date when the actual lighthouse was originally built.

Have Fun! You should have no problems finding a kit to build on the Internet.

References

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