Friday, 30 June 2017

Just how fast do you need to go?

This question has come up more than once recently. And from some pretty strange sources. If someone wanted to view the eclipse from the west coast to the east coast, how fast do you need to go? There are those that have access to aircraft and wondered if it was possible to keep up with the shadow of the Moon as it raced across the continent from Oregon to South Carolina.


As a quick answer, you need to go pretty fast. Like in the range of 1400 to 2400 MPH. That is pretty fast. Supersonic!

The average overall speed would be just over 1600 MHP based on a distance of around 2500 miles in about an hour and a half. At first the speed would be higher, in the 2400 MPH range. That is because the shadow is hitting at an angle. It is more oblong in shape (like a football) but that doesn't matter much because we need to keep up with it. The shadow speed slows as the eclipse reaches the part of the globe that sticks out the most, near Illinois/Kentucky/Tennessee. At that point it is "only" doing about 1400 MPH.

Is there an aircraft that can do it?

Turns out yes, there are several aircraft that might have a chance. The problem is how far can they run at that speed. Most might need to slow way down to fuel up the tanks and by then the shadow has out run them.

In 1973 a prototype of the SST Concorde raced the shadow of the Moon across Africa. It was able to keep up for an astounding 74 minutes before breaking off. The thing is, there are no windows looking up from the Concorde, just a small area for instruments to be placed. They could see out the window, not the eclipse, but the shadow sweeping over the land below.

What about those super spy planes, can't they go that fast? Again, they can but not for long. They go even faster otherwise they might burn up the fuel too quickly. So while they can run at the speed for a short while they would either have to slow down and fuel up or jump way ahead and make a loop about the shadow thus not staying under it the whole time.

14 or 12 states?

If one wanted to see the eclipse from every state that touches the umbra the problem is one of geometry. Up in the air you are outside of the shadow! It is hitting the Earth at a slight angle and is shifted to the South the higher up you go. For 2 of the 14 states the umbra makes a glancing blow at surface level - but not up where the jets fly! I suppose now we need to see what states to the south of the central path might need to be added to the list of states crossed at jet elevations....

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