A paper published in the Astrophysical Journal by a team from the Sloan Digital Sky Survey (SSDS-II) reported that the Milky Way may be as little as half as massive as previous research suggested. Baring in mind that the revised mass is still on the scale of a trillion solar masses (and that the sun has a mass on the scale of 10^30 kg or 1,000,000,000,000,000,000,000,000,000,000 kg), our galaxy is, compared to a human, or even the Earth, quite massive. Want a mental picture?

Suppose we choose for our example a person with a mass of 100 kg. (For those who perfer their units in the English system, this person weighs something like 220 lbs on Earth). This person is 10^28 times more massive than a water molecule. The comparison to the person and the sun is roughly the same also. So a person is to the sun what a water molecule is to a person, in terms of mass at least.

And how does a trillion compare to the number one? Well a strand of hair is on the order of a micrometer thick. There are a million micrometers in a meter and a billion micrometers in 1 km. There are a trillion micrometers in 1000 km. So put together a trillion strands of hair, width wise, and you have 1000 km, which is something like 621 miles.

So the galaxy is huge…and there are likewise a huge number of galaxies in the universe!

There is a nice press release at Science Daily which quotes two Big 10 university astronomers, including one from MSU (in fact I remember Prof. Beers talking about SSDS during the first astronomy class I took at State).

SSDS is a pretty cool colaboration, using a very fascinating setup, and their data is online, free to the public. Even if you don’t have a professional use of the data, check out the web page because there are some great educational resources!