How often do these satellites pass over the same area?
From NCERTAsked by Anonymous from Dallas, United States23 Oct 2026, 7:20 PM ISTUpdated
In one line
How often a satellite passes over the same area depends on its orbit and speed.
Indian National Satellite System — Series of multipurpose geo-stationary satellites launched by ISRO INSAT, an Indian satellite that provides weather and communication services. Image: Wikipedia
The rule
The time it takes for a satellite to pass over the same spot on Earth again is called its revisit time or repeat cycle.
There is no single formula for all satellites, but for a simple polar satellite: Revisit time = (Number of orbits to cover Earth × Orbit period)
Let's understand it simply
Imagine a satellite as a bus flying in circles around the Earth. If the bus goes around the whole city (Earth) in 90 minutes, it will see different places each time. But the city (Earth) is also spinning. So, the bus will not pass over the exact same spot every round. It takes a few rounds before the bus and the city line up again. That is when the satellite passes over the same area.
How it works
The satellite moves in its path (orbit) around Earth.
Earth is spinning below the satellite.
Each time the satellite comes around, the ground below has moved.
After a certain number of orbits, the satellite and Earth line up so the satellite is above the same spot again.
This time gap is the revisit time.
How a satellite revisits the same area
Satellite orbits Earth
Earth spins below the satellite
Each pass covers a new area
After a set number of orbits, the satellite returns over the same spot
The story behind it
When scientists first launched satellites, they wanted to take pictures of the same place to see changes (like weather or crops). They noticed that the time between two pictures of the same place depended on the satellite's path and speed. This led to careful planning of satellite orbits for weather, mapping, and spying.
Where you see it in real life
Weather satellites: Indian satellites like INSAT pass over the same area many times a day to give weather updates.
Google Maps images: The satellite photos you see are taken on different days, depending on the satellite's revisit time.
TV news about cyclones: Meteorologists use satellite images taken every few hours to track storms.
Farmers checking crops: Satellites pass over fields every few days to monitor crop health.
Disaster management: After floods, satellites pass over the area to show new images for rescue teams.
Why it matters
Helps predict weather by showing cloud movement every few hours.
Useful for farmers to track crop changes over time.
Important for rescue teams to get updated images after disasters.
Used in science to study forests, rivers, and cities changing over months or years.
Common mistakes
Thinking all satellites pass over the same spot every day. (Some do, some take days or weeks.)
Mixing up geostationary satellites (which always see the same area) with polar satellites (which move over different areas each time).
Believing that satellite images are always live or real-time (most are hours or days old).
Remember it
A satellite's revisit time is like a bus schedule—it depends on its route and speed. Not every satellite sees your area every day!
Check yourself
What is 'revisit time' for a satellite?
The time it takes for a satellite to pass over the same area again.
Why don't all satellites pass over your city every day?
Because their orbits and Earth's spin mean they cover different areas each pass.
How is a geostationary satellite different from a polar satellite in terms of area coverage?
A geostationary satellite always stays above the same area, while a polar satellite moves over different areas each time.
Quick recap
Revisit time is how often a satellite passes over the same area.
It depends on the satellite's orbit and Earth's rotation.
Some satellites revisit daily, others take days or weeks.
Geostationary satellites always see the same area; others move.
Satellite images are not always live—they depend on revisit time.
