What is the Harvard spectral classification?

1901 Annie Jump Cannon constructed this classification:

Class Temperature in K Color
O >= 30000 blue
B 10000 – 30000 blue white
A 7500 -10000 white
F 6000 – 7500 yellow white
G 5200 – 6000 yellow
K 3700 – 5200 light orange
M 2400 – 3700 orange red

Mnemoic: Oh, Be A Fine Galaxy, Kiss Me

What is Beta decay?

Beta decay is the process where a nucleon decays into either an electron or a positron.

β decay (electron emission)

n → p + e + ν

A neutron decays into proton, an electron and an anti-neutrino.

β+ decay (positron emission)

p → n + e++ νe

A proton decays into a neutron, a positron and an electron neutrino.