Praseodymium - Periodic Table of Videos
The team at periodicvideos has created a TED-Ed Lesson for every element of the periodic table. This one is about praseodymium, an element used to filter harmful light. Praseodymium has even helped slow light's speed down to a mere 300 meters per second!
The name, "praseodymium", is derived from the Greek “prasios didymos”, meaning green twin; it is one of two elements that makes up the mixture didymium. Its oxide is a striking green color.
Why do you think it is important to have an International System of Units, in this case regarding temperature? Do you know the SI units of other physical measurements?