The discovery began with astronomer Henry Draper, who was a pioneer in stellar spectroscopy. When he died, his widow donated money to the Harvard College Observatory. There are hired a group of "computers", who studied the stellar spectra. One of employees classified the spectra by the of their . She ordered them . This scheme proved to shedding any understanding on the nature of stars. Annie Jump Cannon realized that she could reorganize the system into a more natural order. This left us with OBAFGKM. are the hottest and are the coolest

What happens to the light rays when they hit the specimen?

Abeam of electrons with of wavelength of 7.5 x 10-6 m is incident on a pair of narrow rectangular slits separated by 0.75 mm. the resulting interference pattern is projected onto a screen 10.0 m from the slits. what is the separation of the interference maxima in the resulting interference pattern?

Click the game tab at the bottom of the simulation and select level 1. (there is no seesaw balance for this part of the activity.) balance the first equation, and click check to see if you got it right. if you can’t balance it in the first try, you can try again. work through the five equations for level 1. click continue to go on to level 2, and later level 3. each level is more difficult than the one before. keep trying until all the equations are balanced. in one or two sentences, describe how you did in the balancing game. in a few more sentences, explain one strategy you learned for balancing more complex equations.