Equinox - Equinoxes of Other Planets

Equinoxes of Other Planets

Equinox is a phenomenon that can occur on any planet with a significant tilt to its rotational axis. Most dramatic of these is Saturn, where the equinox places its normally majestic ring system edge-on facing the Sun. As a result, they are visible only as a thin line when seen from Earth. When seen from above—a view seen by humans during an equinox for the first time from the Cassini space probe in 2009—they receive very little sunshine, indeed more planetshine than light from the Sun.

This lack of sunshine occurs once every 14 years and 266 days. It can last a few weeks before and after the exact equinox. The most recent exact equinox for Saturn was on August 11, 2009. Its next equinox will take place on April 30, 2024.

One effect of equinoctial periods is the temporary disruption of communications satellites. For all geostationary satellites, there are a few days around the equinox when the sun goes directly behind the satellite relative to Earth (i.e. within the beam-width of the ground-station antenna) for a short period each day. 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 a few minutes to an hour. (For a given frequency band, a larger antenna has a narrower beam-width and hence experiences shorter duration "Sun outage" windows.