Jupiter at Opposition -- closest approach for 2011

The Autumn evening sky is being dominated by one bright, shiny object: the planet Jupiter, which will be a highlight for several months in our skies. On October 28th, Jupiter reaches "opposition" in which it is in a line with the Earth and Sun (and no, that is not what has been causing the recent earthquakes in the San Francisco Bay Area!).

Image Courtesy NASA

When Earth travels around in its orbit, approximately every 13 months we have a close encounter with Jupiter. When we do, the gas giant looks impressive with or without a telescope. Without a telescope, Jupiter is extremely bright, easily 50 times brighter than the brightest stars in the sky right now. It rises due East just after sunset, and remains visible the entire night. Through a small amateur telescope, Jupiter is a fine target, easy to locate and impressive with bands across its disk and the four Galilean moons shining brightly. Now is the time to get out a telescope or binoculars and share the brilliance of Jupiter with someone.

Jupiter's closest approach to Earth

Today Jupiter is at its closest point to Earth for 2010, a mere 368 million miles. Although not a particularly astonishing event, it is nonetheless a prime time to get out your binoculars or telescope to view the giant planet as it dominates the night sky. Jupiter is a fun target to view up close because it offers so much to see: Four bright Moons, colors and textures from its cloud belts, and for a brief time right now it guides you to find the distant planet Uranus.

Every year as the Earth moves around the Sun, at some point in time it is at its closest approach to Jupiter. This moment is called "opposition" and is when the Earth, Sun and Jupiter are all in a perfect line. Each year the distance between the Earth and Jupiter might be a bit more or less depending upon the circumstances of each planet's orbit. This year, the distance is smaller than usual (closest since 1963 and until 2022), but that difference is relatively small from year to year. More important is that the planet is at its brightest for the year, and remains high in the sky for optimum viewing for the entire night.

Sky and Telescope Magazine has an excellent article about this close encounter if you want more details.

Mars and the Biggest Full Moon of 2010

The next few days offer a chance to see Mars and the full Moon together while each celestial body passes through its closest point to the Earth in their orbit. When Mars and Earth line up in their orbits around the Sun, we call that "opposition" and it represents the closest approach between the two planets. This takes place approximately every two years and when it does, Mars appears brighter than usual and is larger in a telescope. Also at opposition, Mars rises just as the Sun sets and is up all night. Mars is at opposition on Friday January 29th.

The Moon has an elliptical orbit around the Earth and as such, each orbital period (approximately 29 days) it is a bit closer to Earth (called Perigee) and then a bit farther from Earth (called Apogee) This month, the Moon is full and is at Perigee on the same date, Friday January 29th. It is also next to Mars so when you look outside on Friday evening, you'll be seeing a nice lineup of a couple of our nearest neighbors. When the Moon is at Perigee, it is a considerably bigger object in the sky than usual. The website Spaceweather.com highlights this nicely in their article.

I have written about the biggest full moon of the year in a previous blog post, if you want to get more information about that subject.

Regarding Mars and opposition, there was a great deal of hype in August 2003 when Mars had a particularly close opposition and was inaccurately stated as "being as big as the Full Moon." That won't ever happen, of course, but it certainly inspired a lot of people to take a look at Mars that summer. This week Mars will be less bright and big compared to 2003 but still a worthy binocular or telescope target. The next close encounter that will rival the 2003 lineup will be in 2018. For an extremely detailed chart and description of the Mars opposition phenomenon, visit the seds.org site.

Mars arrives in the evening sky

Mars is back on display, now visible shortly after sunset in the eastern sky. During the month of January it will reach "opposition" when it appears exactly opposite the Sun in the sky. At opposition Mars is also at closest approach to Earth (and is therefore at its brightest for the year). It shines a distinctive red-orange color especially when compared to the stars in Leo and Cancer that surround it. Through binoculars or a telescope Mars appears as a small colorful dot of light. This week the Moon serves as a guide for locating Mars.