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Answer 1

Answer:

The time it takes for light from objects in space to reach Earth means that when we look at planets, stars and galaxies, we're actually peering back in time. When we look up at the stars, we are looking back in time. The light entering our eyes from these distant objects set off years, decades or millennia earlier.Alpha particles (a) are composite particles consisting of two protons and two neutrons tightly bound together (Figure 1). They are emitted from the nucleus of some radionuclides during a form of radioactive decay, called alpha-decay.