An Erg is an Ant Pushup

Sometimes it’s hard to visualize things in science, particularly astronomy. The scales involved are so large, our brain just doesn’t do anything with the information. There’s just no real frame of reference for some of these concepts so they literally go over our heads.

We need to be able to visualize in some fashion in order to understand. We form pictures in our minds that relate what we’ve learned with things we already understand.

That’s why I loved the above phrase when I first heard it from John Bally, one of my astronomy professors at the University of Colorado. John is an outstanding teacher, one of the few I encountered in my studies. He has a great knack for boiling down concepts to little sound bites that you can take with you, both to an exam and through life.

I never forgot that ditty. It is a brilliant and easy way to visualize the size of the unit. For those who don’t know, an erg is a unit of energy used by astronomers in the so-called CGS system of units. CGS stands for centimeter-gram-second and is essentially an agreed upon method of applying units to astronomical calculations. Basically, if you measure a length in centimeters, then any corresponding masses or weights used in the math should be in grams and time units should be in seconds. Also, energy units should be in ergs.

Physicists use the MKS (meter-kilogram-second) system of units and the corresponding energy unit is the Joule. It’s just an agreement used by scientists so they can keep the math consistent and the numbers involved easier to remember because they are familiar.

An erg is very tiny, as the ant pushup reference suggests. It is way smaller than a Joule; there are 10,000,000 (ten million) ergs in a Joule. There is one Joule of energy in an ant hill of 10 million. I have no idea how big ant hills can actually get, but I don’t thing they get that large.

So, an erg of energy is an ant pushing a 2 gram mass moving at one cm/sec. Ants can do that in their sleep.

It’s always been a bit of a mystery to me why astronomers use the CGS system of units, the numbers are smaller than MKS and since everything in astronomy involves huge numbers, wouldn’t you want to keep them as small as you can? It just seems easier to work with, I mean 10^7 is a big difference. It’s probably one of those ‘It’s always been done this way’ kind of things.

Here are some typical energies in ant pushups:

• A 100 watt light bulb puts out 1,000,000,000 (one billion) ant pushups per second.
• One megaton of TNT is equal to 4.2e22 ant pushups.
• The Sun emits 3.86e33 ant pushups per second (386 billion billion megawatts)
• A typical solar flare is equivalent to 10e27 (a billion billion billion) ant pushups per second
• A typical supernova will put out more ant pushups than the Sun would over ten billion years, about 10e50 (I’m not gonna bother with the billions thing because now things are getting ridiculous).
• The Big Bang: about… oh never mind.

Just thought you’d like to know…

Photo Credit: Tarotastic’s Flickr photostream

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