“Astronomical Site Selections Past”

Just where shall we put that billion-dollar telescope? A good place to start is to look at where observatories have been built in the past and figure out why they were built in those particular locations.

Factors that have been included in the choice of an observatory site include: How clear are the skies? How easy is it to get to? How dark are the skies around the site?

The world map below shows the sites of important observatories around the world in the last 400 years. Observatories built before 1900 are in yellow, the observatories built after 1900 are in red. There is not much overlap. Why?

Mosaic of the Earth, with numbered telescope locations (as described below)

Your initial challenge is to look through the list of the observatory sites below and examine each one. The number of each observatory in the list below corresponds to the same number on the map. The observatories are given in chronological order.

  1. Describe the surrounding of each observatory: plain or mountain? Forest, desert, or city? Land or ocean? Use Google Maps to visit each site. Copy-and-paste either the city and country name or the longitude and latitude provided for each site into the Search window of Google maps, and you will be taken to the observatory site. Some of the older observatories no longer exist, but you can see the type of location they were built in.

  2. Find out what the weather is like at each observatory. Use rainfall as a representation of the number of cloudy nights at each. Visit web sites like Weather.com to get temperatures and rainfall estimates.

  3. How easy is each observatory to get to? Is it near a city? Does it have roads?

  4. How dark is the sky around the observatory? Visit the DMSP site at the National Geophysical Data Center and look at maps of the Earth at night. Look at the location of each observatory on the maps and make a comparison of how bright the sites are to each other (for example: on a scale of 1 to 10….).

From your exploration, describe what you think the important factors were before 1900, and what the important factors were after 1900? If there is a difference, explain why you think the changes occurred.

Telescope/Observatory List (selected)

  1. Telescope (aperture, type): Galileo’s Telescope; 20x, 16 mm clear aperture
    Year Built: 1609
    Location: Padua, Italy
    Elevation: 12 m
    Interesting Facts: Primary lens was more like 2" in diameter, but because it was difficult to maintain an accurate figure near the edges of the lens, it was stopped down to less than 1". The glass also used to have a greenish tint (due to iron) and bubbles, further limiting its clarity. Due to the poor glass quality, many telescopes were nearly useless, and people could truthfully claim that they saw nothing. Galileo spent a lot of time convincing himself that what he saw in his telescope really were just enlarged versions of what he saw with the naked eye.

  2. Telescope (aperture, type): William Herschel’s 49" reflector
    Year Built: 1789
    Location: Bath, England
    Elevation: 17 m
    Interesting Facts: Last used in 1815, destroyed in a gale 1839. Mirror was made of polished Speculum metal, a copper-tin alloy.

  3. Telescope (aperture, type): Lord Rosse’s Leviathan, 6 foot reflector
    Year Built: 1845
    Location: Birr, Ireland
    Elevation: 75 m
    Interesting Facts: Mirror was made of Speculum.

  4. Telescope (aperture, type): Harvard’s Great Refractor. 15" aperture; glass lens
    Year Built: 1847
    Location: Harvard University Campus, Cambridge, MA, USA. 71.1300 W, 42.3800 N
    Elevation: 24 m
    Interesting Facts: Largest in US for 20 years. First star image:* a daguerreotype of Vega in 1850.

  5. Telescope (aperture, type): Grosse Refractor, 0.67 m aperture, glass lens
    Year Built: 1880
    Location: Vienna Observatory, Vienna University, Austria
    Interesting Facts: The "Great Refractor" was the largest telescope in the world when it was built. By the early 20th Century, its usefulness was limited by the growing city of Vienna.

  6. Telescope (aperture, type): 36-inch Refractor, Lick Observatory
    Year Built: 1888
    Location: Mt Hamilton, CA, USA. 121.6366 W 37.3433 N
    Elevation: 1290 m
    Interesting Facts: Lick Observatory was the first permanently occupied mountaintop observatory. James Lick, whose paid for the observatory as a memorial to himself, is buried under the pier of the 36". The observatory now has six major telescopes, including a 3 meter reflector.

  7. Telescope (aperture, type): 40-inch refractor, Yerkes Observatory
    Year Built: 1897
    Location: Williams Bay, Wisconsin, USA. 88.5566 W 42.570 N
    Elevation: 334 m
    Interesting Facts: The 40" is still the world’s largest refracting telescope.

  8. Telescope (aperture, type): Hooker 100" Reflecting Telescope
    Year Built: 1917
    Location: Mt. Wilson Observatory, Mt. Wilson, Ca, USA. 118.057 W 34.2256 N
    Elevation: 1742 m
    Interesting Facts: The 100" provided the data that led to the discovery of the expansion of the universe, and the solar telescopes first showed the existence and importance of magnetic fields on the Sun. Mt Wilson has the steadiest air of any location in North America, but the lights of nearby Los Angeles has limited its usefulness.

  9. Telescope (aperture, type): Hale 200-inch reflector, Palomar Observatory
    Year Built: 1948
    Location: Palomar Observatory, Palomar Mountain, California, USA. 116.8633 W 33.35667 N
    Elevation: 1706 m
    Interesting Facts: the 200" was the technical marvel of the world when it was built. At twice the diameter of the next largest telescope at the time, the 200" reigned as the world’s largest for 25 years, and remained the world’s best until 1992. The Palomar Observatory currently has five major operating telescopes.

  10. Telescope (aperture, type): Mayall 4 meter
    Year Built: 1973
    Location: Kitt Peak National Observatory. 111.60 W 31.963 N
    Elevation: 2120 m
    Interesting Facts: When built, the Mayall telescope was the world’s second largest optical telescope. Kitt Peak, with 23 major telescopes, has the largest and most diverse group of astronomical instruments in the world. Telescopes observe in the optical, infrared, and radio, and include the world’s largest solar telescope.

  11. Telescope (aperture, type): Blanco 4 meter, reflector
    Year Built: 1974
    Location: Cerro Tololo, Chile. 70 48.4 W 30 10.2 S
    Elevation: 2215 m
    Interesting Facts: The Blanco telescope was the largest in the Southern Hemisphere for a quarter of a century.

  12. Telescope (aperture, type): 3.9-meter Anglo-Australian telescope
    Year Built: 1974
    Location: Anglo-Australian Observatory in Coonabarabran, Australia, 149° 03' 57.91" E 31° 16' 37.34" S
    Elevation: 1164 m
    Interesting Facts: This is the largest optical telescope in /Australia, known for spectacular stellar photography. The AA Observatory currently has two major telescopes.

  13. Telescope (aperture, type): BTA-6 6 m reflecting telescope
    Year Built: 1974
    Location: Mt Pashtoukov, Caucasus, Russia. Special Astrophysical Observatory of the Russian Academy of Sciences. Offices: 43.826167 N 41.586683 E, Observatory Dome: 43.6533 N 41.4417 E.
    Elevation: 2100 m
    Interesting Facts: Although the largest optical telescope in the world from 1974 to 1992, numerous problems prevented BTA-6 from doing as well as predicted. However, its computer-controlled altazimuth-style mount has been adopted by every large telescope ever since.

  14. Telescope (aperture, type): 4.2-meter William Herschel Telescope
    Year Built: 1987
    Location: European Northern Observatory, Isla La Palma, Canary Islands. 17 52.9 W 28 45.62 N
    Elevation: 2396 m
    Interesting Facts: The observatory has one of the largest collections of telescopes in the world, and it is perched on the edge of a cliff overlooking a huge volcanic caldera.

  15. Telescope (aperture, type): Keck 1 & 2, twin 9.8 m reflecting telescopes in separate domes.
    Year Built: 1992 (Keck 1), 1996 (Keck 2)
    Location: Mauna Kea, Hawaii, Hawaii. 155 28.5 W 19 49.6 N
    Elevation: 4160
    Interesting Facts: Primary mirrors consist of 36 hexagonal segments. Mauna Kea is one of the premier telescope locations in the world. There are currently 13 major telescopes on the mountaintop, including some of the world’s largest.

  16. Telescope (aperture, type): Very Large Telescope Array:** Four 8.2 m telescopes
    Year Built: 1999-2000
    Location: European Southern Observatory, Cerra Paranal, Chile. 70.405 W 24.628 S
    Elevation: 2635
    Interesting Facts: This state-of-the art observatory features four nearly identical 8.2-meter telescopes and four 1.8 meter telescopes that can act as one Very Large Telescope.

  17. Telescope (aperture, type): Large Binocular Telescope, 11.9 m reflector
    Year Built: 2008
    Location: Mt Graham, Arizona. 109 53.5 W 32 42.1 N
    Elevation: 3181 m
    Interesting Facts: Telescope consists of two 8.4 meters side-by-side, like binoculars. The telescope has the equivalent light-collecting area of an 11.8 meter telescope, and the resolving power of a 22.8 meter telescope.

  18. Telescope (aperture, type): 11-meter Southern African Large Telescope
    Year Built: 2008
    Location: Sutherland, South Africa. 20.81 E 32.376 S
    Elevation: 1798 m
    Interesting Facts: The mirror consists of 91 hexagonal segments operating as one mirror. It is the largest telescope in the southern hemisphere.