Which scientist used cepheid variables to measure the distance to faint "nebulas" in our sky, proving they were actually whole other galaxies?

*drag each tile to the correct location in the sequence* the table shows chronological events in the life of our sun, a medium-sized star. place the missing events into the correct rows of the table.

Find the magnetic field a distance r from the center of a long wire that has radius a and carries a uniform current per unit area j in the positive z direction.

How many neutrons does plutonium -196 with an atomic number of 78.