How did people studying lunar eclipses learn that Earth is round? (A) They observed Earth's shadow on the moon.
(B) They observed the moon's shadow on Earth.
(C)
(D)
They observed that lunar eclipses can last for hours.
They observed that solar eclipses are shorter than lunar eclipses.

Scientists have studied eclipses since ancient times. Aristotle observed that the Earth's shadow has a circular shape as it moves across the moon. He posited that this must mean the Earth was round. Another Greek astronomer named Aristarchus used a lunar eclipse to estimate the distance of the Moon and Sun from Earth

an ion is a charged atom or molecule. it is charged because the number of electrons do not equal the number of protons in the atom or molecule. an atom can acquire a positive charge or a negative charge depending on whether the number of electrons in an atom is greater or less then the number of protons in the atom.