The Astronomical Reason Why Barns are Red

Have you ever noticed that barns tend to be painted red?  Ever wondered why?  Keep reading to learn the astronomical reason why barns are red.

Barns are big. They require a lot of paint.  So it makes sense to choose the least expensive paint available.

Red pigment is the cheapest, which makes red paint the least expensive.  So that’s why barns tend to be red. But why is red a cheaper pigment?

Red pigment is cheapest because it’s the most abundant natural pigment found on Earth.  Why is red the most abundant pigment?

It’s the most abundant because it’s made from two of the most common elements on Earth, oxygen and iron.  The chemical formula is Fe₂O₃, which is ferric oxide or Hematite. 

Hematite is a very common mineral on Earth’s surface.  It is found in sedimentary, metamorphic, and igneous rocks all over the world.  It is composed of about 70% iron and 30% oxygen.  

NASA has also discovered that hematite is one of the most abundant minerals on Mars.  This why we call Mars “The Red Planet” – its surface has a high concentration of this reddish material.

When you crush hematite to a fine powder, it can be used to make paints that tend to be opaque and permanent.  Great for barns!

Iron is by mass the most abundant element on Earth.  And the iron in your hemoglobin is why your blood is red.  But why is iron so common?

Iron is the most abundant metal on Earth because it was the most abundant metal found in the protoplanetary disk from which the Earth was formed.  How did the iron get there?

The Remnants of A Supernova and Protostar Phase of the Sun

Billions of years ago, a very large star many times more massive than our Sun was reaching the end of its life.  The delicate balance between the crushing gravity trying to implode the star and the outward pressure caused by nuclear fusion was about to be upset. 

The star had fused hydrogen into helium, and then oxygen and carbon, and so on down to element #26: iron. The core of the star was almost pure iron.  After iron is created by the fusion process, normal fusion stops in a star. When that happens, within less than a second gravity wins and the star is compressed to unimaginable temperatures and pressures. 

The star blew up in a cataclysmic supernova explosion, and a huge cloud of gas was expelled in all directions.  Eventually, motion by a passing star caused some of this gas – rich in iron – to begin to coalesce, and it began to collapse on itself and start to spin due to conservation of angular momentum.

It would have looked much like the Orion nebula does to us today, where many stars are being formed in a rich cloud of gas.  Eventually, this cloud of gas formed one of many protoplanetary disks, and our Sun was born, and soon after this Earth. So the short answer is, barns are red because of how massive stars die.

References

1. St. Patrick’s County Park Red Barn. Credit: https://creativecommons.org/licenses/by-sa/3.0
2. Protoplanetary Disk. Credit: European Southern Observatory