A station is the moment when a planet, seen from Earth, appears to stand still against the zodiac before it changes direction. A planet stations retrograde when its forward motion stops and it begins to drift back, and it stations direct when that backward drift ends. The planet never actually stops in its orbit. The pause is an effect of viewing one moving body from another.
Mercury, Venus, Mars, and the outer planets all station. The Sun and the Moon do not, because from Earth they always move forward through the signs. Around a station the planet moves very slowly, so its degree barely changes for several days. For a slow outer planet the near-standstill can last for weeks. Mercury usually turns retrograde three times a year, and each retrograde period begins and ends with a station.
The astrology calendars list stations for Mercury through Pluto with their UTC times, and the year overview shows each retrograde period from the station where it begins to the station where it ends. The personal transit calculator keeps direct and retrograde passes separate, and the sky explorer flags a planet that is near a station.
For the full cycle between two stations, read the retrograde entry and the guide to retrogrades. A station can also coincide with an ingress when a planet turns close to a sign boundary.
In a chart
Suppose a daily ephemeris shows Mercury’s longitude growing by smaller and smaller steps, then holding at almost the same degree, then decreasing. The station retrograde is the instant between those rows when the daily motion changes from forward to backward. A birth chart drawn near that instant shows Mercury marked as stationary or just retrograde, depending on the software’s threshold. A planet that stations close to a natal position can also pass over the same degree more than once, which is why a single transit can repeat.
Where you see it on Astrologican
These free tools and pages calculate or list it, so you can see it in a real result.