Astronomical Observing Techniques

If photodissociation was an important process for CO in the early Solar System, it may also have been important for N2, an isoelectronic and isobaric molecule, which had an abundance in the gas phase lower than CO by only a factor of six. Nitrogen is less usefiil than oxygen as a tracer of Solar System chemistry, for a number of fundamental reasons (1) it has only two stable isotopes, so that there is no simple way to distinguish between mass-dependent and abundance-dependent isotope effects (2) the homonuclear character of the N2 molecule renders it invisible to most astronomical observational techniques ... 

II. Millimeter Astronomical Observing Techniques II. Science at Millimeter Wavelengths... 

The spatial resolution of astronomical observations varies over several orders of magnitude from 1-100AU, depending on the observing technique, whereas the extraterrestrial chondritic sample suite predominantly represents materials that... 

Very Long Baseline Interferometry Technique in which astronomical observations are carried out by separate radio telescopes thousands of miles apart, then combined to form a single image. 

The first faltering steps of molecular astronomy were intimately related to the birth of modern spectroscopy. It was the discovery at the beginning of the nineteenth century that the Sun and stars are composed of the same elements as the Earth, which led astronomers to the idea that spectroscopic techniques can be used to observe cosmic chemical processes. 

Though much effort has been made during the last 10 years to detect primary molecules in comets by radio techniques only a few positive results could be achieved (for a review of this very complex subject and for a table of negative results see Snyder It should be emphasized that these observations are very difficult and that the signals are only marginal in most cases. Furthermore, it is not always easy to coordinate the cooperation with radio astronomers in due time when a bright comet appears. With respect to the importance of these observations, all efforts should however be made to continue the search for molecules in the microwave and radio spectra of future comets. 

A radical is defined to be a molecule in an open shell electronic state. It is often, although not necessarily, very reactive and short-lived in a laboratory environment. Several new species have been studied since the publication of the previous supplement, although the number for which microwave transition frequencies have been measured is still quite small. Many of the new observations have been made by radio astronomers who now have access to frequencies up to 350 GHz. Experiments employing double resonance techniques (simultaneous irradiation with microwaves and either infrared or visible radiation) have also made a contribution to the development of the field. The information about linear molecules, in 2, 2, and states, is contained in section 3.2.1. The non-linear radicals, almost all of which are triatomic, are presented in 3.2.2 (Non-Unear triatomic) and 3.2.3 (Non-linear larger molecules). 

Interference from the Earth s atmosphere has always been a problem for optical astronomers, especially when attempting to view surface details on the terrestrial planets such as Mercury or Mars. Planets with dense atmospheres such as Venus also present a problem for astronomers because their thick cloud layers prevent direct surface observations. To overcome this difficulty, in the 1950 s, astronomers developed a technique using radar imaging to reveal surface features. Radar signals can easily penetrate clouds and are reflected back by items they hit. By... 

Modem extraterrestrial (satellite and radio astronomical) techniques are inherently three dimensional. Simultaneous observations at two points yield 3D coordinate differences that can be added directly to the coordinates of the known point A on the earth s surface to get the sought coordinates of the unknown point B (on the earth s surface). Denoting the triplet of Cartesian coordinates (x, y, z) in any coordinate system by r and the triplet of coordinate differences (Ax, Ay, Az) by Ar, the 3D position of point B is given simply by... 

In the short term, observations will bring information about source populations beyond that available using current astronomical techniques. Direct detections will... 

Because of the faintness of its radio emission, Pluto was the last planet to be detected. A few asteroids, satellites, and comets have been measured as well. Nonthermal radio emission has been measured from Jupiter, Saturn, Uranus, Neptune, and Earth. In this article we give an overview of the techniques used by planetary radio astronomers and discuss what has been learned from the measurements and what can be done in the future. In the interest of brevity, we do not discuss specific observations of asteroids and satellites, although they rightfully belong in any discussion of planetary radio astronomy. 

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