Astronomers cannot typically perform experiments: the objects of interest in the field are far away. Consequently they rely primarily on observations, collectingelectromagnetic radiation or particles such as cosmic rays. Some experiments on planets in the solar system are now possible via remote controlled spacecraft. Some of the measurements astronomers perform includeastrometry (positions of celestial bodies),photometry (light flux),spectroscopy (intensity vs wavelength), and imaging.[1]: 1
Historically, astronomy was more concerned with theclassification and description ofphenomena in the sky, whileastrophysics attempted to explain these phenomena and the differences between them usingphysical laws. Today, that distinction has mostly disappeared and the terms "astronomer" and "astrophysicist" are interchangeable. Professional astronomers are highly educated individuals who typically have aPhD inphysics or astronomy and are employed by research institutions or universities.[3] They spend the majority of their time working on research, although they quite often have other duties such as teaching, building instruments, or aiding in the operation of an observatory.
TheAmerican Astronomical Society, which is the major organization of professional astronomers inNorth America, has approximately 8,200 members (as of 2024). This number includes scientists from other fields such as physics,geology, andengineering, whose research interests are closely related to astronomy.[4] TheInternational Astronomical Union comprises about 12,700 members from 92 countries who are involved in astronomical research at the PhD level and beyond (as of 2024).[5]
Contrary to the classical image of an old astronomer peering through atelescope through the dark hours of the night, it is far more common to use acharge-coupled device (CCD) camera to record a long, deep exposure, allowing a more sensitive image to be created because thelight is added over time. Before CCDs,photographic plates were a common method of observation. Modern astronomers spend relatively little time at telescopes, usually just a few weeks per year. Analysis of observed phenomena, along with making predictions as to the causes of what they observe, takes the majority of observational astronomers' time.[citation needed]
Astronomers who serve as faculty spend much of their time teaching undergraduate and graduate classes. Most universities also haveoutreach programs, including public telescope time and sometimesplanetariums, as a public service to encourage interest in the field.[6]
Those who become astronomers usually have a broad background in physics,mathematics, sciences, andcomputing in high school. Taking courses that teach how to research, write, and present papers are part of the higher education of an astronomer, while most astronomers attain both aMaster's degree and eventually a PhD degree in astronomy, physics orastrophysics.[7]
PhD training typically involves 5–6 years of study, including completion of upper-level courses in the core sciences, a competency examination, experience with teaching undergraduates and participating in outreach programs, work on research projects under the student's supervising professor, completion of aPhD thesis, and passing a finaloral exam.[7] Throughout the PhD training, a successful student is financially supported with astipend.[7]
While there is a relatively low number of professional astronomers, the field is popular amongamateurs. Most cities have amateur astronomy clubs that meet on a regular basis and often hoststar parties. TheAstronomical Society of the Pacific is the largest general astronomical society in the world, comprising both professional and amateur astronomers as well as educators from 70 different nations.[8]
As with anyhobby, most people who practice amateur astronomy may devote a few hours a month tostargazing and reading the latest developments in research. However, amateurs span the range from so-called "armchair astronomers" to people who own science-grade telescopes and instruments with which they are able to make their own discoveries, createastrophotographs, and assist professional astronomers in research.[9][10]
Kennedy E (1956),A Survey of Islamic Astronomical Tables; Transactions of the American Philosophical Society, vol. 46, Philadelphia:American Philosophical Society
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