This is just the inverse of time. The standard
unit, Hertz, is equal to once per second
. There's an implicit one
of what ?
question involved in that: when the answer to that is
cycles of some repeating system, especially when that repeating system is
rotational, there is some sense in distinguishing the quantity from an inverse
time. Rates of rotation, in particular, are better described as angle/time:
the standard notion of frequency is implicitly one turn divided by the period
of the repeating process, but commonly ends up being handled in terms of the
result of dividing this by radian.
Hubble's
constant, which guages the rate of expansion of the universe, is arouhd
2.27 atto Hertz (albeit more usually expressed in kilometres per second per
mega-parsec, for which it's in the low seventies, or kilometres per second per
light year, for which it's in the low twenties). This isn't really
the frequency
of anything but, if it were, the period would be around
14 giga years – the age of the universe.
The central bar of the Milky Way galaxy spins at 1.8
femto Hertz; the Sun orbits the galactic centre at 0.14 fHz and the spiral
arms (pressure-waves, in the inter-stellar gas, that trigger star-formation)
circulate round the galaxy at about 0.63 fHz. The last few million years of
Earth's history have seen a cycle
of glaciation with a frequency of
roughly 0.3 fHz. The Earth's
orbit's eccentricity
fluctuates, due to gravitational perturbations from other planets, with a
frequency of about 77 fHz.
The axis about which the Earth spins precesses, tracing out a cone at a frequency of about 1.2 pico Hertz. The Earth's orbit's elliptical axis rotates, resulting in a relative frequency of around 1.4 pHz in the relationship between seasons and orbit. The angle between Earth's spin axis and plane of orbit varies (between 67.9° and 65.5°) with a frequency of 0.77 pHz.
The Sun follows a roughly eleven-year cycle of variation
in activity; at solar minimum
it has few sun-spots and little dramatic
activity; activity increases from there to a solar maximum
with many
sun-spots and much activity, then decreases again to another minimum after
roughly eleven years – so with a frequency of 2.88 nano-Hertz. The
planets orbit The Sun with frequencies: 132 nHz (Mercury), 52. nHz (Venus),
31.6875361 nHz (Earth), 16.85 nHz (Mars), 2.671 nHz (Jupiter), 1.072 nHz
(Saturn), .38 nHz (Uranus), .191 nHz (Neptune).
At solar minimum, coronal mass ejections happen about once per week – at a frequency of about 1.7 µHz; at solar maximum, the rate goes up to about twice per day – or more – or a rate of 23 µHz. In the early twenty-first century, humanity as a whole was launching about one rocket bound for space each week.
The ISS orbits Earth with a period of 90 minuts, i.e. a frequency of 5/27 mHz.
Standard long-playing
vinyl records ran on a 100/3
RPM turn-table; this turns at a rate of 5/9 turns/second. There are roughly
forty lightning flashes on
the Earth per second
(or 44 times per
minute – sources conflict).
The rotors in the GE90 jet-engine spin at 10,400 RPM, i.e. 0.173 kHz.
In the part of CERN's new (due open in May 2008) Large Hadron Collider specialized for study of the beauty quark, LHCb, the frequency of proton-proton interactions shall be 40 MHz – 40 million collisions per second.
Electromagnetic radiation with a frequency of 1 GHz has a wavelength of one light nanosecond, which is roughly one foot. Mobile telephones using GSM (Global System for Mobile communications) operate at frequencies of 0.85, 0.9, 1.8 and 1.9 GHz (hence wavelengths of about 35, 33, 17 and 16 cm; a.k.a. 14, 13, 6½ and 6¼ inches). Higher frequency electromagnetic radiation, with frequencies from around 3 to around 300 GHz, are generally described as microwave (despite actually having wavelengths of a millimetre and more, rather than microns). The processing rhythm of modern computers ticks along at a few GHz; I'm typing this (in 2017) on a computer (from 2009) whose four processors each run at 1.3 GHz (when they're busy; they spend most of the time idle).
Infrared radiation has frequencies in the range from around 0.3 to around 400 tera Hertz (and micron-scale wavelengths).
Visible light is electromagnetic radiation with frequencies
roughly in the range from 0.4 to 0.75 peta Hertz; ultraviolet light
has
frequencies in the range from there up to around 30 PHz. Electromagnetic
radiation at higher frequencies gets described as X-ray or gamma ray; the
distinction is mostly based on what processes (is believed to have) generated
them.
Written by Eddy.