If you have ever had the urge to contribute to science, a total lunar eclipse offers a great opportunity.

It is easy to do, is open to all ages and does not require special training or equipment of any kind; just use your eyes to rate the intensity of the “blood moon.” No, we are not going to count red corpuscles, but we will give the eclipse a number from 0 to 4, with 0 indicating an extremely dark appearance and 4, just the opposite. And then e-mail your estimation to Joe Rao, an associate of Hayden Planetarium. He will combine every estimate sent his way into a scientific measurement of the state of our atmosphere on Jan. 20.

French astronomer Andre’-Louis Danjon introduced the scale in 1921 and here is how to judge the brightness of the eclipse:

0 – Very dark, almost invisible at mid-totality

1 – Dark, gray or brownish in coloration. Lunar features are distinguishable only with difficulty.

2 – Deep red or rust-colored eclipse. Very dark toward center of umbral shadow, though relatively bright at its outer edge.

3 – Brick-red eclipse. Umbral shadow usually has a fairly bright gray or yellow rim.

4 – Very bright copper-red or orange eclipse. Umbral shadow has a bluish, very bright rim.

As a reference, this contributor gave the eclipse of 2013, shown in accompanying graphic, a “3.” Be sure and e-mail your estimate to skywayinc@aol.com and become a member of the contributing scientific community.