Question

what was discovered in 1965 and is believed to be leftover thermal energy from the big bang?
o red shift
o the eagle nebula
o the doppler effect
o background radiation

Explanation:

• Red - shift is related to the Doppler effect in astronomy (the change in wavelength of light due to the motion of the source, often used to study the expansion of the universe, but not the leftover thermal energy from the Big Bang).
• The Eagle Nebula is a star - forming region in our galaxy, not related to Big Bang leftover energy.
• The Doppler effect is a general physical phenomenon (change in frequency/wavelength of a wave due to the relative motion of source and observer), not the specific leftover from the Big Bang.
• Background radiation (cosmic microwave background radiation, CMBR) was discovered in 1965. It is the afterglow or leftover thermal energy from the Big Bang, which fills the universe uniformly.

Answer:

Background radiation.