The Inner Planets: Mercury, Venus, and Mars

The Inner Planets: Mercury, Venus, and Mars — page 7
THE INNER PLANETS MERCURY Venus AND MARS larger than Mercury However Mercury is larger than the dwarf planet Pluto For some 75 years when Pluto was classified as a planet Mercury was considered the second smallest planet Mercury is the densest planet in the solar system followed by Earth if one takes into account the planets internal compression because of gravity Mercury is unusually dense because it is composed of a high per centage of metal The metal is concentrated in a comparatively huge core which accounts for nearly 75 percent of Mercury s diameter AppEARANCE FROM EARTH Mercury can be seen from Earth without a telescope It always appears close to the Sun within about 28 angular degrees For this reason the planet can only be seen near the horizon At certain times of the year it appears as a morning star just before sunrise while at other times it appears as an evening star just after sunset Because Mercury's orbit lies between Earth s orbit and the Sun Mercury displays phases like those of the Moon and the planet Venus These phases can only be seen with the aid of a telescope Mercury sometimes 12