What Stratum is, and why
Stratum is a small archive of short films about the physical Earth: rivers and glaciers watched over decades, the shape and height of the sea surface, storms, eruptions and what follows them. There are 17 films and a handful of still photographs. All of them were made by NASA and are in the public domain.
The films already exist in the agencies' own catalogues, alongside thousands of others: press briefings, narrated features, data products for specialists. Stratum exists to pick out the few that can be understood by simply watching, and to put them where they are easy to find, easy to show to a room and easy to download.
How films are chosen
A film is kept if it shows a process happening rather than explaining one: a shoreline moving inland, a storm closing around its eye, a lake growing where ice used to be. Films with narration, presenters or title cards are left out, because the aim is to leave room for the viewer, or the teacher, to do the explaining.
Nothing is edited. The file you watch and download is the file the source published, at its original length; only the poster frame is ours. Each film is checked to be a United States government work, and its catalogue number is recorded so the original can be found again. The films are then sorted twice: by subject into collections, and into series that put a few of them in a deliberate order.
How the captions are written
Every film has one caption of one or two sentences. It says what is on the screen, where, and over what period, based on the source's own description. It does not tell you what to feel about it. Under the caption is a shorter note, “What to look for”, which points at one thing in the frame that is easy to miss on a first viewing.
Each series has two paragraphs of its own: why its films belong together, and in what order to watch them.
Who it is for
Teachers who want a minute of real footage to open or anchor a lesson. Students who need a primary source rather than a summary of one. And anyone who would rather watch a river cut off its own meander than read that rivers do.
Using it in a classroom
- Play a short Landsat film on a loop, without introduction, and ask what changed. Then read the caption together.
- Pause on the first frame and the last. Most of the long-term films are easiest to read as a before and after.
- Use a series as a lesson plan: the order is already set, and the introduction says what links the films.
- Download the films in advance. Nothing on the page depends on a connection once the file is saved.
Licence and trademarks
As works of the United States government, the films and photographs are in the public domain. You may show, copy and share them; we ask only that the source credit on each film page travels with the file. Agency names, logos and insignia are not covered by the public domain and must not be used to suggest endorsement. Their appearance in a credit line here does not mean any agency endorses this archive. Full source details are on the credits page.
How the site works
The site is a set of static pages and a folder of video files. There are no accounts, no forms, no cookies, no analytics or tracking, and no third-party scripts; the typefaces are served from this site./p>