Answer:
By measuring it's Radical velocity using Doppler Phenomenon...
Explanation:
It is done by measuring the absorption spectrum produces by a star as a result of measuring Doppler's relative wavelength. The star with the lower speed must have lower absorption spectrum extent as compared to the faster one.
Hey there! The answer to your first question is SILICON, Nickle has 28 protons, silicon has 14, 14+14=28. Its the only element thats adds up. I dont know about the 2nd one myself.
The top of a wave is called the crest.
Hope I helped! :D