Astronomy

Vernal equinox (spring equinox) for this year will occur on 20 March, 05.48 UTC. The moment marks the first day of spring season in Northern Hemisphere, and autumn in Southern Hemisphere.

In the southern hemisphere, the vernal equinox corresponds to the center of the Sun crossing the celestial equator moving southward. It is also the points on the celestial sphere where the ecliptic and equator cross and the vernal equinox is used as the zero point in measuring star co-ordinates.

One of the effects of equinoctial periods is their temporary disruptive effect on communications satellites. For all geostationary satellites, there is a point during the equinox when the sun is directly behind the satellite relative to Earth (i.e., within the beamwidth of the groundstation antenna). The Sun’s immense power and broad radiation spectrum overload the Earth station’s reception circuits with noise and, depending on antenna size and other factors, temporarily disrupt or degrade the circuit. The duration of those effects varies but can range from an hour to a few minutes. (For a given frequency band, a larger antenna has a narrower beamwidth, hence experience shorter duration “Sun_outage” windows).

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