On the night of June 2, 2014, the moon is waxing, appearing as a fatter crescent higher in the sky after the sun goes down. If you look, you can use the moon somewhere around 60 to 90 minutes after sunset, to identify the dazzling planet Jupiter, planet Mercury and the two Gemini stars Castor and Pollux. You’ll notice Jupiter first. It’s the brightest object in the vicinity of the waxing crescent moon. Then look for Mercury, lower in the sky, not much above the horizon. See how the curve of the moon’s lighted crescent points (like an arrow) toward Mercury? Use binoculars if you need them to find Mercury before it sets.
Mercury, the innermost planet of the solar system, orbits the sun in only 88 Earth-days. Even though Mercury has the shortest year of any solar system planet, it also sports the longest day. One day on Mercury is equal to 176 Earth-days. On Mercury, one day is twice as long as its year of 88 Earth-days.
If you lived on Mercury, you’d see the sunrise in the east, then the sunset in the west some 88 Earth-days later. However, when Mercury reaches perihelion – its closest point to the sun for the year – you’d see the sun stop, then go eastward for a while before resuming its normal westward motion. If you were on the right place on Mercury, you could actually watch the sun rise, go back under the eastern horizon, and then rise again. By the way, Mercury will be at perihelion on July 29, 2014.
Just as on Earth, the westward movement of the sun during a day on Mercury is due to the planet’s rotation. However, Mercury’s orbital motion is so fast at perihelion that it causes the sun to go eastward in the daytime sky for a few (Earth) days.
Bottom line: At evening dusk on June 2, 2014, look for the strange and intriguing planet Mercury below the waxing crescent moon and Jupiter. Also look for the two brightest Gemini stars, Castor and Pollux, close to Jupiter.