As an astronomy educator here at the National Air and Space Museum, I’ve had the opportunity to interact with thousands of visitors, especially in our Public Observatory. I’ve enjoyed the many chances to discuss the wonders of the Universe and to answer visitors’ astronomy-related questions. However, I tend to dread the month of August because of an internet hoax involving Mars that’s been plaguing e-mail inboxes for seven years. The e-mail in question is commonly referred to as the “Mars Hoax” or, more accurately, the “Mars Spectacular,” and is titled: "Two moons on 27 August or The Red Planet is about to be spectacular!" It informs recipients that Mars will have an extremely close encounter with Earth during the month of August, culminating on August 27th when Mars is approximately 34 million miles away. The information in the previous sentence was only true during the month of August in 2003. This was a historic astronomical event. Mars was the closest it had been to Earth in 60,000 years. However, this already happened. Before I get into the e-mail’s misinformation, let’s talk about what actually happens when Earth and Mars have a close encounter. Imagine two people are running a race around a track. One person is running in the innermost lane while the other is running in the outermost lane. The runner in the inside lane will complete one lap faster than the other person. This is similar to Earth’s and Mars’ orbits around the Sun. Earth takes 365 days to complete a lap around the Sun while Mars completes a lap in 687 days. If the runners continue running, eventually the runner on the inside (Earth) will catch up with the runner on the outside (Mars). When this occurs in the solar system, it is called opposition. It also means that Mars is opposite of the Sun in the Earth’s sky. An opposition for Mars occurs approximately every 2 years. The last three occurred on November 7, 2005, December 24, 2007, and most recently on January 29, 2010.
Why was the Mars opposition in 2003 so special? Most oppositions bring Earth and Mars between 34 and 63 million miles from each other. This is mainly due to Mars’ elliptical orbit. All planetary orbits are slightly elliptical meaning that a planet's distance to the Sun changes as it moves in its orbit. When it's closest, it’s called "perihelion" and when farthest, "aphelion." Mars' orbit is more elliptical than Earth’s. Every 15 to 17 years, Mars is in, or very close to, its perihelion point just as Earth “catches up” with Mars. This brings the two planets especially close together. In 2003, this perihelic opposition occurred on August 27, when Mars was closest to the Sun, and Earth near its most distant point from the Sun. This combination brought the Earth and Mars unusually close together. As a result, Earth and Mars were 34.6 million miles away from each other; the closest they had been in 60,000 years. If you missed this historic event, you may be wondering what Mars looked like in the sky during August of 2003. According to the most recent versions of the Mars Spectacular e-mail, Mars will appear “as large as the full moon to the naked eye.” That’s huge! No wonder people are still excitedly forwarding this e-mail to everyone they know. The original e-mail, though, stated, “At a modest 75-power magnification Mars will look as large as the full Moon to the naked eye.” This is more or less true, just misleading. It’s referring to how Mars could appear if magnified 75 times by a telescope eyepiece. To see any significant detail on the Martian surface rather than a large, red, fuzzy blob one would have to peer through a telescope with an objective mirror or lens larger than 8 inches; a much larger telescope than what department stores sell.
To the naked eye, Mars appeared as a bright, reddish, star-like object during the 2003 opposition. It was twice as bright as Sirius, the brightest star in the night sky, but not quite as bright as Venus appears this month. Compared to the full Moon, Mars was only 1/75 of its size – certainly not a second Moon in the sky. Those who forward the Mars Spectacular e-mail probably don’t consider the implications of Mars appearing that large. Mars is around twice the size of our Moon. It would be have to be located at twice that distance (480,000 miles) for it to appear the same size – 33 million miles closer than it ever gets to Earth. If Mars does appear as our “second moon,” something has gone terribly wrong with the inner solar system or the laws of physics.
The Mars Spectacular e-mail is still circulating. I know three people who received it in the past month from well-meaning relatives. One reason it still has life is because the actual year of the event was dropped from the e-mail text. Therefore, every August people receive this e-mail and believe Mars will be close to Earth that year. Unfortunately, “2010” has mysteriously appeared in recent versions of the e-mail which definitely does not allow the e-mail to go away quietly. If you have received the Mars Spectacular e-mail, believed it to be true, and passed it along to friends, family, or perhaps even a news outlet, it’s okay. You’re not the first one to fall for its thrilling message and you certainly won’t be the last. A good lesson to come from the Mars Spectacular e-mail is: if it’s too fantastic to be true, it’s probably not. Being internet savvy means you know where to find trustworthy sources and can weed out the misinformation. To check the validity of e-mail content, one of the best online resources is Snopes. You’ll find the “Mars Hoax” in the #12 spot of their Hot 25 list of urban legends. NASA, as well as astronomy magazine sites such as Sky and Telescope and Astronomy are also good online astronomy resources. Disappointed that you won’t be able to see a “spectacular” Mars? Don’t fret! Mars is viewable in the evenings throughout the month of August, 2010. It is currently low in the southwestern horizon after sunset, hanging out with Saturn and a very bright Venus. Check Sky & Telescope’s weekly “sky at a glance” page for observing tips and information on other astronomical events.