Let the moon guide you to two planets and a bright star as darkness falls on Saturday, August 2, 2014. The planets Mars and Saturn, plus the star Spica, should be visible, in spite of the glare of tonight’s wide waxing crescent moon. Note the change of the moon’s position since August 1.
Mars, the fourth planet outward from the sun, is the solar system planet that’s most like Earth in a number of respects. The inclination of Mars’ rotational axis (25.2o) is almost the same as Earth’s (23.4o), and a day on Mars (24.66 hours) is just a touch longer than a day on Earth (24 hours). Mars is one of the four inner rocky planets – Mercury, Venus, Earth and Mars – all of which have solid surfaces. The outer four planets – Jupiter, Saturn, Uranus and Neptune – have no solid surfaces whatsoever.
What are the spin axes of the other planets in our solar system like? The spin axes of Mercury and Venus stand almost straight up and down relative to the plane of their orbits around the sun. That’s why these worlds don’t exhibit seasons the way that Earth and Mars do. Meanwhile, Saturn and Neptune – having axial tilts of 26.7o and 28.3o, respectively – do not greatly exceed the axial tilt of our planet Earth. But Saturn is a gas giant, and Neptune is an ice giant. They are not rocky worlds, with solid surfaces, like the Earth and Mars.
There’s going to be an exciting event later this year in the vicinity of Mars. The Comet C/2013 A1 Siding Spring will sweep close to the planet – many times closer than any known comet in Earth’s sky – on October 19, 2014. Comet Siding Spring’s tiny nucleus, or core, will miss Mars by about 82,000 miles (132,000 kilometers), but its trail of dust particles might be wide enough to reach Mars and encounter its thin atmosphere … or might miss it, too. If the comet dust does reach Mars, it has the potential to damage our spacecraft in orbit there. NASA has been maneuvering the craft to keep them safe.
Bottom line: Watch as the moon appears closer to Mars on August 2, 2014. It’s also now moving closer to Saturn and will be very near it as the moon and planets come out at this time tomorrow, at nightfall on August 3.