Inner planets visible this week
Posted September 3, 2015
Whether you are up before the sun or are more likely to see a sunset in your daily routine, you have a chance to see one of the inner planets of the solar system for the next few days.
Look to the west after sunset for Mercury. It will be faintly visible about 8º above the horizon to the left of the setting sun. It wont be very bright because only its western hemisphere is illuminated right now. It would only ever appear full to us as it hides behind the sun. Mercury will continue to sink before setting about an hour after sunset.
Mercury’s innermost position in the solar system keeps it close to the sun, making it difficult to see most of the year. The next few days are our best chance to see this elusive planet because it is positioned at the greatest elongation for the year today. Elongation is the angular separation we see between a planet and the sun as viewed from Earth.
Mercury’s orbit takes it around the sun every 88 days, but that orbit is far from circular. Where it appears in our sky in relation to the sun varies significantly as a result. The next good chance to catch a glimpse of Mercury will be before sunrise the first week of February and then again after sunset in mid August.
For you early risers, Venus is even easier to spot shining brightly in the eastern sky before sunrise for the next few months. Also look to the left of Vvenus for dimmer and slightly orange/red Mars. Each is visible without the aid of a telescope.
Note the position of Venus over the next few weeks. It will continue to rise higher in the sky throughout September and October reaching its point of greatest elongation the morning of Oct. 26. Venus may even be visible during daylight hours in late October, more on that later.
Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems. You can follow him on twitter @rtphokie.