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Describing Very Low Frequency Radio Waves

A hectometre (hm) is a unit of length equal to 100 metres, and it is used to describe very long wavelengths in the Very Low Frequency (VLF) and Low Frequency (LF) bands of the electromagnetic spectrum. Wavelengths in the hectometre range correspond to frequencies between approximately 3 kHz and 3 MHz. These long wavelengths are typically used for maritime navigation, military submarine communication, AM radio broadcasting, and time signal transmissions.

For example, a signal at 300 kHz has a wavelength of 1 kilometre, or 10 hectometres, and a signal at 1 MHz corresponds to 3 hectometres. These long wavelengths have the unique ability to travel long distances and penetrate water and the ground, which is why they are used in submarine communications and emergency broadcast systems.

Using hectometres to express wavelength offers a practical scale for understanding wave propagation over great distances. It also aids in antenna design, where very large antennas—often hundreds of metres long—are needed to efficiently transmit or receive these frequencies. Understanding wavelength in hectometres is important in geophysics, radio astronomy, and large-scale communications infrastructure.

Understanding Low-Frequency Oscillations

The millihertz (mHz) is a unit of frequency equal to 10⁻³ hertz, meaning one cycle occurs every 1,000 seconds or roughly 16.7 minutes. This low-frequency range is important in fields such as seismology, astrophysics, and geophysics, where it describes slow, periodic events that unfold over minutes to hours.

In astrophysics, millihertz frequencies are commonly observed in solar oscillations and stellar pulsations, providing key information about the internal structure and dynamics of stars. These oscillations help scientists understand energy transport, magnetic activity, and the life cycles of stars.

In geophysics, millihertz frequencies correspond to long-period seismic waves generated by earthquakes or volcanic activity. These waves travel long distances through the Earth’s interior and can reveal valuable data about its composition and structure.

Additionally, millihertz frequencies are relevant in oceanography and atmospheric science for studying tides, slow atmospheric waves, and other natural cycles that influence climate and weather patterns.

Because millihertz oscillations have relatively long periods and wavelengths, they allow researchers to probe processes that develop over extended timeframes and large spatial scales, bridging the gap between faster waves and ultra-low-frequency phenomena.