Mars as big as the Full Moon … NOT!

Wednesday, August 24th, 2005 at 12:11 PM by Juan

Several of us SCSU astronomers have been questioned by our friends about an email that is circulating around many people’s inboxes that states that the planet Mars is going to make its closest pass to Earth in a long time on August 27th and that it will “look as big as the full moon.” Any astronomer will tell you this is pure bunk or to quote Patrick Wiggins (a NASA representative) “If we really did see Mars as big as the moon, it would be a really bad day because it would probably mean we’d all die.”[1]

Many amateur astronomers will recall that Mars did in fact make an remarkably close approach to Earth on 27 August 2003. On that date, Mars came within 35 million miles of Earth, its closest approach to Earth in 60,000 years (a time well before the Americas were inhabited by humans)! Apparently, someone decided to ‘replay history’ two years later and then distort the truth in the process.

At Snopes.com (a wonderful website to look up any too good to be true emails) they quote a 2003 email that was sent about the 27 August 2003 event:

The encounter will culminate on August 27th when Mars comes to within 34,649,589 miles of Earth and will be (next to the moon) the brightest object in the night sky. It will attain a magnitude of -2.9 and will appear 25.11 arc seconds wide. At a modest 75-power magnification Mars will look as large as the full moon to the naked eye. Mars will be easy to spot. At the beginning of August it will rise in the east at 10p.m. and reach its azimuth at about 3 a.m.[2]

From what I can tell, the information in the above quote is correct for the 2003 event. In fact, I noticed something very similar to the current batch of emails. Notice that email states that in a modest telescope, “Mars will look as large as the full moon.” I suspect that someone grabbed this email, removed the bit about the modest telescope and changed the year from “2003″ to “2005″ … voila, instant Mars Hoax!

Mars at 1am on 27 Aug 2005
(Click on image for full size version)
Mars (and the Waning Crescent Moon) as they will appear over the eastern horizon at 1 am CDT on August 27, 2005 in Saint Cloud, MN. This image was generated using Starry Night Pro 5.0 by Imaginova.

As if any additional debunking is needed, the 2003 email I quoted is correct in that on 27 August 2003, Mars was about 35 million miles away[3] had a visual magnitude of -2.9, and appeared about 25 arcseconds in angular diameter (about 72 times smaller than the Full Moon). However, on 27 August 2005, Mars will be about 64 million miles away (over 80% farther than two years earlier), it will have an angular diameter of about 13 arcseconds (half the size it did during the 2003 event), and it will have a magnitude of -0.9, or about 6.3 times fainter than two years before. The Full Moon is typically about 140 times larger than this in diameter and about 63,000 times brighter! The current email going around the internet is wrong on almost every factual point except that Mars will be visible in the night sky!

Finally, I note that there is nothing special about the 27th of August in terms of distances between Earth and Mars. In fact, Earth and Mars will be moving closer together during the next few months, until the evening of October 29-30, when Mars will makes is next “closest approach” to Earth. On October 29th, Mars will be Mars will be 43 million miles away, with a magnitude of -2.15 (about 2 times fainter than during the 2003 event), and an angular diameter of about 20 arcseconds (about 20% smaller than during the 2003 event) and 90 times smaller than the full moon.

Links with more information:

Note added August 24: Looks like Phil Plait, the Bad Astronomer, now has placed an article online about this “Mars as Big as the Moon” thing. He comes to some similar conclusions that I did regarding its origin. More importantly, he has the complete text of the email that is being sent around this time.

Linknotes:
  1. See Mars really big . . . or will you? - The quote is from this article in the Salt Lake Tribune ↩
  2. Snopes.com Mars Article - The full email is quoted here. ↩
  3. The distance was not correct to the precision they state in the email! ↩

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