A planet in today's sky forming an aspect with a point in your birth chart.
The birth chart is fixed; the sky keeps moving. Transits are where the two meet. Those of fast planets last hours or days, those of Saturn or Pluto years. SideraMea also computes each one's time window — when it enters orb, when it is exact, when it leaves — because knowing *how long* is half the information.
Reading a transit in your chart
Every transit has three ingredients. The transiting planet brings the theme of the moment: Mars initiative, Saturn testing, Venus pleasure and connection. The natal point shows which part of you is being called on. The aspect sets the tone, smoother with trines and sextiles, more demanding with squares and oppositions.
The natal house the planet is crossing matters too: astrologers read it as the area of life where the theme shows up. Saturn in your tenth house, for instance, is traditionally read as a time of taking stock of your work and public role, rather than as one specific event.
Why some transits last for years
It comes down to speed. The Moon goes round the zodiac in about twenty-seven days, so its aspects last a matter of hours; Saturn takes about twenty-nine years to complete a circuit.
Then there is retrograde motion. Seen from Earth, a planet periodically appears to move backwards, so it can cross the same point three times: forwards, back and forwards again. A slow transit can therefore enter orb, leave it and come back months later. SideraMea allows transits an orb of 3° (2° for the sextile) and, for each active one, pins down the current pass: when it entered orb, when it is exact and when it leaves.
Frequently asked questions
What is the difference between a transit and a natal aspect?
A natal aspect links two planets in your own chart and is fixed at birth, so it stays the same all your life. A transit links a planet in today's sky to a point in your chart, so it keeps changing. The orbs differ too: up to 8° for natal aspects, 3° for transits, because a passing contact only counts when it is close to exact.
Are Saturn transits always bad?
No. Saturn has a reputation as the heavy planet, but traditionally it stands for structure, responsibility and the passage of time that tests what is solid. Its transits are often read as phases of consolidation: demanding, but also the moment when something lasting gets built. Much depends on the point touched and the aspect formed.
When do you feel a transit most, when it starts or when it is exact?
Traditionally the peak is the exact aspect, but many astrologers find that the themes of a slow transit surface as soon as it enters orb and only fade after it leaves. With fast planets the distinction hardly matters. With slow ones, knowing the start and end dates helps you read the transit as a period rather than a single day.
See it in your own chart
Calculating your birth chart is free: wheel, planets, houses, aspects and a first reading. All you need is your date, time and place of birth.