This red supergiant star [V838] monocerotis is located about 20,000 light-years from Earth. A burst of light in a huge dust cloud caused light echos that were seen for three years. Credit: NASA, ESA and H.E. Bond [STScI].
What is an Atomic Clock?
The watches we wear on our wrists or the clocks we put on our walls are not atomic clocks. There are not all that many true atomic clocks - and they tend to be rather large and expensive. So, unless it looks something like the picture alongside from the National Institute for Standards and Technology [NIST], it is not a state-of-the-art atomic clock.