Sea Level! What is it and how do scientists calculate it? As it turns out, there are actually many complexities in determining this measurement. For example, Earth isn’t actually a sphere, gravity is stronger and weaker at different points around the globe, and of course, there are a lot of mountains that are no where near water — so how do we know what sea level would be? In this video, Minute Physics explains the details.
After you’ve watched, check out these related links: ellipsoid, geoid, geodesists, Mount Everest, Chimborazo Volcano, Space.com’s Best Gravity Map Yet Shows a Lumpy, Bumpy Earth, and this clarifying and not-to-be-missed animated gif of Earth’s gravity field.
In the archives: videos about or involving measuring things, including Measuring the Universe.
We can now “fly over” topographically accurate landscapes of Mars thanks to Mars Express, the European Space Agency (ESA) mission to explore the red planet. Launched in June 2003 and arriving six-and-a-half months later, the Mars Express spacecraft has orbited the planet almost 12,500 times, better revealing Mars’ turbulent climatic history. It’s expected to continue orbiting and gathering data until the end of 2014.
From Slate’s Phil Plait:
I saw quite a few landmarks in there, including Olympus Mons, the tallest volcano in the solar system; Valles Marineris, the longest rift valley in the solar system (it’s wider than the Grand Canyon is long!); an elongated crater I’ve written about before (at the 2:20 mark, and shown at the top of this article); and the ridiculously gorgeous and very weird swirls in the terrain at the Martian north pole (though the south pole of the planet is even more jaw-droppingly beautiful).
I was also intrigued by a crater shown at the 1:50 mark, which looks like it got filled by a landslide off a nearby hill. Mars isn’t what you might call geologically active, but it does commonly suffer landslides and avalanches when the frozen carbon dioxide ice under the surface sublimates (turns directly from a solid into a gas), which can dislodge material. If that happens at the top of a hill or cliff, material can cascade down dramatically. I strongly suspect that’s what we’re seeing in this video.
Taken with the satellite’s High Resolution Stereo Camera, the video was released by the DLR German Aerospace Center.
In the archives: more satellites, more maps, and more Mars.
Alaska: The Nutrient Cycle by wildlife filmmaker Paul Klaver.
Once they enter fresh water chum salmon stop feeding and morph into an aggressive creature intent only on mating. After spawning, they die and their bodies become a source of nutrients for everything in the forest and sea.
This 14 minute video had the kids riveted and shows how the end of the salmon’s life directly benefits the animals and ecosystem around them. A note a warning for more sensitive viewers: this video includes a lot of creatures eating very dead-looking fish.
There are more videos tagged with life cycle and death in the archives, including Radiolab’s excellent Whale Fall.