Astronomical measurements

Following a millennial tradition, most astronomers measure optical fluxes in magnitude units. A magnitude is defined as ... 

The microgravitation lens (microlens) method Astronomical measurements... 

The fourth method, astronomical measurement, is (like the Doppler method) based on the observation and measurement of tiny motions of a star which are due to the mass(es) of the orbiting planet(s). A primary goal of the Space Interferometry Mission (SIM) is the discovery of planets similar to Earth, which orbit around stars like the sun. The SIM is due to start in 2009, and the measurements carried out will increase the accuracy of determinations of distances of stars in our galaxy several hundred times. Exact information can be found in the catalogue which forms part... 

Astronomical measurements have some limitations not present in laboratory investigations but a detailed knowledge of the spectra of atoms and molecules can be used to overcome the restrictions of resolution and atmospheric windows. The detailed knowledge is the key to this success, however, and confidence in the conclusions of astrochemical observations must come from the understanding in the laboratory. 

Today we would hesitate to comment on the energy or entropy of the universe, because we have no way to measure these quantities, and we would refer only to the surroundings that are observed to interact with the system. Some cosmological theorists have suggested that the increase in entropy posmlated by the second law is a result of the expansion of the universe [6]. One recent set of astronomical measurements leads to a prediction that the universe will continue to expand, and another predicts that expansion will reach a maximum and reverse [7]. 

Astronomical measurements reveal that about 90 percent of the mass of the universe is invisible to us. This invisible matter, also known as dark matter, is likely to be exotic" matter—very different from the elements that make up the periodic table. What do you think dark matter might be made of How soon might we know the answeT ... 

Length. The original metric standard for the length of a meter was one ten-millionth part of a quadrant of the earth s meridian. Astronomical measurements (at that time) indicated that one-tenth of a quadrant of the earth s meridian was measured between Dunkirk, in France, and a point near Barcelona, Spain. This distance was dutifully measured and divided by one million to obtain the meter. It is fortunate that the meter was later redefined, because if you take what we now call a meter and measure the distance between the Dunkirk and Barcelona points used, you get the length space of 1,075,039 meters. This space is an accuracy of only 7.5 in 100 meters. 

The abundances of carbon relative to the other elements has been measured in stars and in the interstellar clouds and ionized nebulae. These measurements derive from high-resolution spectroscopy of spectra from stars, from the strength of forbidden line emissions and of ultraviolet lines from ions in nebulae, and from millimeter radio spectroscopy in interstellar clouds (see 12C, Astronomical measurements for a summary). 

A different chemical mechanism has been found in diffuse molecular clouds (see Astronomical measurements, above) by ultraviolet astronomy. Ultraviolet light capable of disrupting the CO molecule penetrates much deeper into CO-containing... 

Although variations of the isotopic abundance ratio 5°V/51V are expected in presolar grains, they are notlikely to be measured in the near future owing to the great rarity of 5°V. Astronomical measurements are even less likely. 

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