Mars: Bright, But Not as Big as the Full Moon!

Posted Updated
Jesse Richuso

Back in August of 2003, Earth passed within 35 million miles of Mars. It the closest the two planets had been in the past 60,000 years. The event made headlines around the world, and we hosted "MarsFest" here at Morehead Planetarium and Science Center. What the news stories didn’t tell you is that Earth actually gets relatively close to Mars every 2.2 years when Earth “laps” Mars as the planets orbit around the Sun. The distance at each close pass ranges between 35 and 60 million miles.

There has been a popular chain email floating around the internet since the 2003 event about a “Mars Spectacular” occurring in August of each year. Here at Morehead Planetarium and Science Center, we call it the "Mars Hoax Email." When it was first emailed it was innocent and accurate enough, with one poorly constructed sentence:

“At a modest 75-power magnification Mars will look as large as the full Moon to the naked eye.”

It’s technically correct. At the time of the close pass of 2003, through a telescope with a magnification of 75, Mars looked as big as the full Moon does with the naked eye. The important part is “through a telescope.” To the naked eye, Mars will never look anything different than a bright star. Then, some jokester decided to alter that sentence to read:

At a modest 75-power magnification

Mars will look as large as the full Moon to the naked eye

With that line being the only bold (and 20+ font size) text in the email (and this blog post! oh no!), it may have been the only thing that people read before forwarding the email on to their friends and family. The email spread like wildfire and soon people around the world had the misconception that Mars would somehow come close enough to Earth to look as big as the full Moon. For the past four years, we've fielded numerous questions regarding the "Mars Spectacular" from our planetarium guests.

For Mars to look as big as the full Moon, it would have to get within about 500,000 miles of the Earth. It will never, ever happen. It is physically impossible. Remember that Mars at its closest is still 35 million miles away. For comparison, the Moon is about 250,000 miles away.

Earth “laps” Mars every 2.2 years, and we recently had one of those close passes. On Christmas Eve 2007, only 55 million miles separated the two planets (remember, that's relatively close compared to other objects out in space). When Earth and Mars line up on one side of the Sun, Mars is said to be “in opposition.” Opposition is the best time to view Mars because it appears bigger and brighter in our sky. Also, it’s up all night long.

We’re a few weeks after opposition now and Earth is currently moving away from Mars, but Mars will still be worth viewing throughout the remainder of winter. It looks like a very bright red-ish star above the head of the constellation, Orion. The best time to see Mars is in the evening hours, from dusk until midnight. Mars will be at its highest point in the sky during that period.

Come out to Jordan Lake's Ebenezer Church Recreation Area for Morehead's monthly skywatching session on Saturday, January 12, 2008 from 6 to 8 p.m. We'll be observing Mars and a crescent Moon. For more information on skywatchings sessions, visit Morehead's skywatching webpage.

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