ASTR 130 (O'Connell) Lecture Notes

7. MODERN OBSERVATIONAL ASTRONOMY


HST on Orbit

The Hubble Space Telescope in orbit. Click for enlargement.


A. INTRODUCTION

The human imagination has never been a match for the universe. That is why astronomy, more than any other science, has been regularly revolutionized by new observational discoveries. Since 1610, these have depended on telescopes. When telescope technology has developed slowly, as in the early 19th century, progress was slow. When technology surged, as in the late 20th century, progress was explosive.

This lecture surveys the state of observational astronomy today, with some background on how we got here. A key theme: to build an instrument at the frontier of performance is always costly in terms of brains and money. Thus, progress has coupled visionary astronomical pioneers with the generosity of wealthy private donors or the financial strength of governments.


Mt. Wilson 100-in

100-in reflector on Mt. Wilson. Click for enlargement.

B. AMERICAN OBSERVATORIES 1880-1950

40-in Optical and mechanical technology in the last few decades of the 19th century had advanced to the point that the construction of large telescopes was feasible. These, however, required substantial private donations. Most were associated with universities. Important developments are listed below (click on the links for more information):


George Ellery Hale was the premier American telescope founder. He planned, successively, the three largest telescopes of their era and lived to build the first two of these. He had a great facility for obtaining private financing, from Carnegie and Rockefeller, among others. The three major Hale telescopes were


8-m Blank

First 8-m mirror blank for the Gemini project, 1996.

C. AMERICAN OBSERVATORIES 1950-2000

The experience of World War II, in which physical science and mathematics provided the key technologies leading to victory, convinced the government that broad-based federal support for basic science and technology was essential. This included astronomy, and since 1950 the federal government has become the largest source of support for research in astronomy. The two dominant sources of funds for astronomy are

Initially, public funding almost completely replaced the private financing responsible for the large telescopes through 1950. But NSF's budget failed to keep pace with the rapidly increasing number of astronomers and the expanding observational opportunities enabled by new technologies. By 1985, astronomers began turning again to private benefactors to finance large ground-based telescopes. The largest individual telescopes built to date, the Keck 10-m telescopes (see Lecture 2), were supported by a private gift of $120 million to Caltech. In the next decade, it is hoped that public/private partnerships will help create telescopes in the 30-100 meter class.

The US lead in state-of-the-art telescopes is now being challenged by European and Japanese astronomers. The European Very Large Telescope, four 8-m telescopes, now has the largest collecting area in the world.

The European Southern Observatory Very Large Telescope, Chile.

D. CURRENT STATUS & EM COVERAGE

Although optical telescopes are the most numerous and also, in many ways, the most useful, astronomers today have access to almost the entire cosmic electromagnetic spectrum described in Lecture 2, ranging from radio waves at the long wavelength end to gamma rays at the short wavelength end. All of the devices for detecting EM waves are called "telescopes," even though some (e.g. radio antennas) look nothing like classical optical telescopes.

The first steps outside the confines of the optical band were taken in the 1930's and 40's when (non-artificial) radio waves were first detected from cosmic objects. Radio astronomy developed rapidly in the 1950's, followed by infrared, ultraviolet, X-ray, and gamma ray astronomy. Since it is absorbed by the Earth's atmosphere, observations of most cosmic EM radiation other than optical and radio require telescope in space (see below).

You can find compilations of information on telescopes at the following websites:

Access to powerful telescopes is provided through a proposal and competitive peer-review process, in which an astronomer (or more commonly, a group of astronomers) submits a detailed proposal which is reviewed in competition with other proposals by a "time allocation committee." There are many more proposals than can be accommodated. For instance, many are always for work on faint objects during "dark of the Moon" time (only two weeks out of each month). One out of two proposals will be successul on "under-subscribed" telescopes, while only one out of five will succeed for more cutting-edge facilities like HST or the Chandra X-ray Observatory. It typically takes astronomers 2-4 weeks to write a competitive proposal.


Astro on orbit

Astro-2 UV observatory in Shuttle payload bay. Click for enlargement.

E. SPACE ASTRONOMY

1. Why telescopes in space?

2. Space telescopes cost up to several 100x as much as equivalent sized ground-based facilities. Why?

3. Examples:

Homework:

Web links: most are embedded in text above.
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Last modified 6 March 2001 by rwo

Images from observatory public sites. Text copyright © 2001 Robert W. O'Connell. All rights reserved. These notes are intended for the private, noncommercial use of students enrolled in Astronomy 130 at the University of Virginia.