Landsat 9
If you have looked at a satellite image of a forest, a city or a shrinking lake, there is a fair chance it came from this programme. Landsat has photographed the land surface continuously since 1972, and Landsat 9 is the current instalment.
What makes Landsat 9 different
It crosses at the same local time, always
Its orbit is sun-synchronous: the plane drifts about a degree a day, exactly keeping pace with Earth’s progress around the Sun. Every image is taken mid-morning local time, so shadows are comparable between passes taken years apart.
An unbroken record since 1972
No other Earth-observation programme comes close. Comparability across five decades is the whole value — which is why each satellite deliberately resembles the last rather than chasing better instruments.
Sixteen days to cover the planet
It images a 185 km swath and repeats the same ground track every 16 days. Paired with Landsat 8 on an offset schedule, most places are looked at roughly weekly.
The data is free
Landsat imagery was opened to anyone at no cost in 2008, and the effect on research, agriculture and disaster response was immediate. It is one of the most-used public datasets in existence.
Landsat 9 launched in September 2021, replacing Landsat 7 and flying alongside Landsat 8. Its inclination of 98.2° is retrograde — slightly more than a right angle to the equator — and that is what makes the orbit sun-synchronous. It is not an engineering coincidence but the point of the design: an image archive is only comparable if the lighting is, so the satellite is arranged to cross the equator at the same local solar time on every single pass. The result is that a farmer, a glaciologist and a city planner can put a 2024 scene beside a 1984 one and trust the difference they see.
Frequently asked questions
What does Landsat 9 photograph?
Land surfaces and coastal waters, in visible, near-infrared and thermal bands — which is how it measures vegetation health and surface temperature, not merely how things look.
How often does it revisit the same place?
Every 16 days for an identical ground track. With Landsat 8 offset by eight days, most locations get coverage roughly weekly.
Is Landsat imagery free?
Yes. The full archive has been openly available at no charge since 2008.
Why 98 degrees and not 90?
A perfectly polar 90° orbit would not stay aligned with the Sun. The slight retrograde tilt lets Earth’s equatorial bulge precess the orbital plane just under a degree a day, matching Earth’s motion around the Sun.