Why do astronomers believe in dark matter?

Dark matter, by its very nature, is unseen. We cannot observe it with telescopes, and nor have particle physicists had any luck detecting it via experiments.

NASA finds tropical storm 14W strengthening

Tropical Storm 14W formed as a depression a couple of days ago in the Northwestern Pacific Ocean and strengthened into a tropical storm on Sept. 2. Infrared data from NASA's Aqua satellite shows some powerful thunderstorms ...

Providing a solution to the worst-ever prediction in physics

The cosmological constant, introduced a century ago by Albert Einstein in his theory of general relativity, is a thorn in the side of physicists. The difference between the theoretical prediction of this parameter and its ...

In search of signals from the early universe

,On a hot morning in early July, a seven-foot wide, 8,000-pound metallic structure made its way from Boston to Penn's David Rittenhouse Laboratory. The large aperture telescope receiver (LATR) was carefully loaded onto a ...

Spinning towards robust microwave generation on the nano scale

Spin-torque oscillators (STOs) are nanoscale devices that generate microwaves using changes in magnetic field direction, but those produced by any individual device are too weak for practical applications. Physicists have ...

Small, nimble CSU satellite has surpassed a year in space

After meeting all its benchmarks for demonstrating small-satellite weather forecasting capabilities during its first 90 days, a Colorado State University experimental satellite is operating after more than one year in low-Earth ...

Tracer galaxies probe the cosmic background

The universe, perhaps surprisingly, is not comprised of galaxies randomly distributed throughout space; that is, it is not very homogeneous. Instead, its galaxies are clustered into distinct structures, typically gigantic ...

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Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz. This broad definition includes both UHF and EHF (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineering often putting the lower boundary at 1 GHz (30 cm), and the upper around 100 GHz (3 mm).

Apparatus and techniques may be described qualitatively as "microwave" when the wavelengths of signals are roughly the same as the dimensions of the equipment, so that lumped-element circuit theory is inaccurate. As a consequence, practical microwave technique tends to move away from the discrete resistors, capacitors, and inductors used with lower-frequency radio waves. Instead, distributed circuit elements and transmission-line theory are more useful methods for design and analysis. Open-wire and coaxial transmission lines give way to waveguides and stripline, and lumped-element tuned circuits are replaced by cavity resonators or resonant lines. Effects of reflection, polarization, scattering, diffraction, and atmospheric absorption usually associated with visible light are of practical significance in the study of microwave propagation. The same equations of electromagnetic theory apply at all frequencies.

The prefix "micro-" in "microwave" is not meant to suggest a wavelength in the micrometer range. It indicates that microwaves are "small" compared to waves used in typical radio broadcasting, in that they have shorter wavelengths. The boundaries between far infrared light, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study.

Electromagnetic waves longer (lower frequency) than microwaves are called "radio waves". Electromagnetic radiation with shorter wavelengths may be called "millimeter waves", terahertz radiation or even T-rays. Definitions differ for millimeter wave band, which the IEEE defines as 110 GHz to 300 GHz.

Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that it is in effect opaque, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.

This text uses material from Wikipedia, licensed under CC BY-SA