The waning crescent moon plus the planets Jupiter, Mars and Mercury greet the early riser before daybreak tomorrow (Saturday, August 3). Look in the eastern predawn sky for the brightest and second-brightest celestial objects of early morning: the moon and Jupiter. If you’ll lucky, you’ll see a faint glow of earthshine on the waning crescent moon. Then search for the fainter planets, Mars and Mercury.
We show the ecliptic on the sky chart at the top of this post. Since all the solar system planets circle the sun on nearly the same plane, the planets are always found on or near the ecliptic – the Earth’s orbital plane projected onto the constellations of the Zodiac.
After you find dazzling Jupiter near the moon, look for the rather faint red planet Mars about 5 degrees below it. For reference, the width of one finger at an arm length approximates 2 degrees of sky. It’s best to look for Mars in the predawn darkness, or at least one and one-half hours before sunrise. Even then, binoculars may come in handy for catching this world that’s nearly 30 times dimmer than the king planet Jupiter.
By the way, if you can spot Mars with the eyes alone, and live at mid-northern latitudes, there’s a good chance of seeing the Gemini stars Castor and Pollux to the north (left) of Mars. You’re also likely to see the constellation Orion – sometimes called the ghost of the summer dawn – to the south (right) of the red planet. The presence of Gemini and Orion in the early morning sky is a sure sign that summer is ebbing toward fall in the Northern Hemisphere.
Look for Mercury, the solar system’s innermost planet, to rise above the horizon some 90 to 75 minutes before sunrise at mid-northern latitudes. This world shines as brilliantly as the sky’s brightest stars but its luster might be tarnished somewhat in the glow of dawn. Binoculars may still come in handy.
Bottom line: On Saturday, August 3, 2013, let the two brightest celestial objects of the predawn and dawn sky – the moon and planet Jupiter – guide you to the fainter planets Mars and Mercury.