An overtaking illusion

Mercury is the closest planet to the Sun and the fastest, moving at about 47 km/s against Earth's 30 km/s. Every 116 days or so it catches up with Earth and passes it on the inside track.

While it passes, Mercury seems to slide backward against the distant stars. It is the same effect as a slower train appearing to drift backward when yours overtakes it. Both planets keep moving forward the whole time.

Rx and D

The turnaround is called a station. Mercury appears to stop, drift back about 9 to 16 degrees across the sky, then stop again and resume its forward path.

The first stop is marked Rx (stationary retrograde) and the second D (stationary direct). They are the two dots on the speed chart on the Today page. Retrograde is the stretch where the line sits below zero.

How often it happens

Most years have three retrogrades and some have four. Each lasts 20 to 24 days. The middle of every one falls close to the moment Mercury lines up between Earth and the Sun.

Does it affect anything on Earth?

No known effect. Even at its closest, Mercury is about 77 million kilometres away, and its pull on Earth is tiny next to the Moon's or the Sun's. Nothing physical changes when it starts to look as if it is going backward.

Other planets do it too

Every planet appears to turn retrograde now and then. Mars and the outer planets do when Earth overtakes them. Venus does when it overtakes Earth. Only the Sun and Moon never do. Mercury simply does it most often.

Why it can feel real

A retrograde covers about one day in five, so a bad day lands inside one fairly often by chance. A missed email during a retrograde gets blamed on Mercury. The same email on a direct day gets blamed on nothing. People tend to remember the matches and forget the rest.

Typical themes

• Misunderstandings and crossed wires.
• Delayed trips, late messages and tech glitches.
• Old contacts, ideas and unfinished business coming back.
• A pull to review, revise, reconnect and rethink.

Common advice

• If you can wait, hold off on signing big contracts or launching something new.
• Put major tech purchases on pause.
• Double-check anything you send or book.
• Use the time to finish and tidy up rather than start.

Shadow periods

Many astrologers count a shadow on each side of the retrograde. The pre-shadow begins when Mercury first reaches the point where it will later turn direct. The post-shadow ends when it climbs back to the point where it turned retrograde. On average each shadow adds about 17 days. The Dates page lists them for every retrograde.

The sign sets the tone

The sign Mercury is in when it turns retrograde is said to colour the theme.

• Fire (Aries, Leo, Sagittarius): impulsive words, short tempers, rushed decisions.
• Earth (Taurus, Virgo, Capricorn): snags with money, work, schedules and practical plans.
• Air (Gemini, Libra, Aquarius): crossed wires in conversations, messages and devices.
• Water (Cancer, Scorpio, Pisces): old feelings, memories and relationships resurfacing.

A note on evidence

Astrology is a tradition and has not held up as a predictive science. Researchers who have looked for reliable links between planetary positions and events or personality have not found them, and the How it works page covers why nothing physical changes. Many people still use a retrograde as a prompt to slow down and double-check.

Good uses of the time

Finish old projects, clear out cupboards and inboxes, review plans before you commit to them, and get back in touch with people you have lost track of. Retrograde suits tasks that start with re-.