Mars reaches opposition in December 2007 as it reaches prime viewing position from Earth and becomes brighter than any star.
Over the past several years now, e-mails describing a Mars looking "as large as the full moon" in Earth's sky have been circulating. But the fact is Mars can never look this large from Earth simply because it is too far away. However, there are times when Mars is in a better position for us to observe it. The end of 2007 is one of those times.
Mars in October 2007
In October 2007, Mars rises late in the evening within the constellation Gemini. Mars is already growing brighter, starting out October at magnitude -0.1 and increasing in brightness to -0.6 by the end of the month. On October 3, Mars will lie less than one degree from the open cluster M35. On October 30, Mars and a 68%-lit moon lie just over six degrees apart. Mars will be brighter than both Castor and Pollux in Gemini and any of the stars to the south in Orion. Note the color: It should appear red or orangish compared to the stars surrounding it.
Mars in November 2007
Mars enters November rising about four hours after sunset, but ends the month rising just two hours after sunset, placing it in prime time evening hours. Mars undergoes another big boost in brightness from -0.6 to -1.3 magnitude. Sirius, the brightest star in the sky, is -1.4. Next month Mars will surpass it in brightness. Mars stays within the constellation Gemini throughout the month. On November 26, Mars and a 90%-lit waning moon come to within one and a half degrees of one another. If anyone asks you "what is that bright star by the moon tonight," you can tell them it is the planet Mars.
Mars in December 2007
Mars starts out the month in Gemini but crosses into Taurus during the final days of the year. It rises earlier every day, and by the solstice it will be above the horizon before sunset. In the third week of December Mars reaches its peak of brightness at magnitude -1.6. It now outshines every star in the night sky. Except for the moon and when Venus rises just before the Sun, Mars dominates all other objects in the night sky.
Mars reaches opposition, or the point in its orbit when it is opposite the Sun in Earth's sky, on December 24. Opposition is typically the best time of year in which to view a planet, because it is up in the sky all night long. On December 23, Mars has another close encounter with the moon. The full moon will pass less than one degree away from Mars. Some portions of the Earth will even see Mars slip behind the moon in an occultation. Note how the bright moon washes out other stars from its region and steals some of Mars's glory compared to when Mars is alone in a dark sky.
Mars makes its closest approach to Earth on December 18. It lies .589 AU away, or 54.8 million miles. As Mars nears Earth, you will not see a large disk like the moon, but the surface of Mars can show up in modest telescopes.
What to Look for When Observing Mars
When Mars comes close to Earth it gives amateur astronomers a chance to see for themselves what is occurring on Mars. We currently have spacecraft on the surface of Mars and in orbit around the Red Planet, beaming back constant information. But you can see surface markings and atmospheric clouds and ice caps with your own eyes. The disk of Mars will appear about 16 arcseconds across in December. (Compare this to the Moon's diameter of 30 arcminutes across. One arcminute equals 60 arcseconds, so you can see how Mars will not look at all like the full moon. Have realistic expectations.) If a dust storm is occurring on Mars, you won't see anything but a solid peach haze. But if it is clear you have a chance to see the brightest features, such as white clouds or a polar ice cap. The polar ice caps on Mars regularly thaw in the spring and refreeze in the fall. If you have an especially large telescope you may see the dark markings on Mars's surface.
