The spectrum of object glowing because of their temperature -- a phenomena called "blackbody radiation" --
was a (no pun intended) "hot topic" in the late 1800s.
Because all types of matter was found to have the same spectrum at the same temperature (more or less),
it was felt that understanding BBR would give insight into the basic nature of matter.
Developing an explanation for what was seen in experiments frustrated the scientific community so much
that Max Planck decided to see if he could develop a mathematical explanation.
He found he could mathematically explain the spectrum by assuming that the light coming from a blackbody
came in discrete parts (he called them "quanta") where the energy of each quanta was equal to a constant
'h' times the frequency of that light,
What he never considered was that his mathematical explanation was what actually WAS HAPPENING
-- that light really DOES come in quanta.
The constant that he used to derive his formula is now called "Planck's Constant,"
Planck's Constant (abbreviated as 'h'), when first "discovered," was found to be the ratio of the energy of
an individual photon to the frequency of that photon's light.
In other words, the energy of a photon is equal to h times the photon's frequency.
It has since been found that h fits into a wide variety of formula that allow us to understand the Universe we happen to live in.
Without this constant, a lot of our Universe would be incomprehensible.
Planck's Constant units are energy-seconds.
It is the constant of proportionality relating the energy of a photon to the frequency of that photon.
Its symbol is h
Planck's Constant is the product of two fundamental Quantum constants, W and C. W is the magnetic charge of
"free space" and C is the electric charge of "free space". The value of W= 500 atto Webers and C= 4/3 atto Coulombs.
The "free space" impedance z is the ratio of the two quantum constants z=W/C = 375 Ohms.
[summary from pages in answer.com]
Values of h
6.62606957(29)×10−34 J/Hz
4.135667516(91)×10−15 eV/Hz
6.62606957(29)×10−27 erg/Hz
1.054571726(47)×10−34 J·s
6.58211928(15)×10−16 eV·s
1.054571726(47)×10−27 erg·s
Read more...
https://en.wikipedia.org/wiki/Planck_constant