Get up an hour or more before sunrise Thursday (July 24, 2014) to view a beautiful morning tableau. The waning crescent moon and planet Venus – second-brightest and third-brightest heavenly bodies, respectively, after the sun – will be together in the eastern morning twilight. The darkened portion of the crescent moon might be shining dimly in earthshine. Basking in wondrous sunshine, these beauties shine by reflecting the light of the sun.
If you’re lucky, you might catch another world Thursday morning beneath the moon and Venus. Look quite close to the horizon, around 70 to 60 minutes before sunrise. This world is Mercury, and it will be surprisingly bright for being so low in the sky. Bring binoculars, though, if you have them.
Mercury is the innermost planet, and it also shines by reflected sunlight. It’s the first planet outward from the sun, and Venus the second, so Mercury and Venus circle the sun inside of Earth’s orbit. Our planet Earth is the third planet from the sun.
The four inner planets – Mercury, Venus, Earth and Mars – are rocky worlds that orbit the sun inside the asteroid belt between Mars and Jupiter. If you could look down upon the north side of the solar system, you’d see all the planets circling the sun in a counter-clockwise (prograde) direction. As a general rule, the planets rotate on their axes in the same direction that they revolve around the sun: counter-clockwise.
However, Venus is a major exception. This world rotates clockwise (retrograde), contrary to the direction of its counter-clockwise (prograde) orbit. On Venus, the sun rises in the west and sets in the east. Some astronomers think Venus initially rotated in a counter-clockwise direction, until a big planet-like object smashed into Venus, turning this world “upside down.”
By the way, our moon rotates on its axis in the same direction that it orbits Earth: counter-clockwise.
Bottom line: Before sunrise on July 24, look for the slender waning crescent moon near dazzling Venus, the “upside-down” planet. They will be prominent in the east before dawn.