Mars is Still Not Going to Appear as Big as the Moon!!!
Published on Aug 8, 2007 at 11:49 pm.
8 Comments.
Filed under Mars, astronomy, observing.
Well, the annual urban legend about Mars being as big as the Moon is making an appearance again. I’ve already gotten several questions about it. This seems to be a never ending problem. Every year, the same email goes around as if it is news. I blogged about this a year ago.
As the planets move around the Sun, the occasionally pass one another. When Earth passes Mars, it is called an opposition. At that time, Earth and Mars are about as close as they are going to be until the next time that they pass one another. But, Earth and Mars both have elliptical orbits, so sometimes one is closer to or farther from the Sun that other times. Because of this, the actual closest approach is often a few days off of the date of the opposition, but never more than a few days off. Every 15 to 17 years, the elliptical orbits of Earth and Mars happen to bring these planets unusually close to one another. The last time that this happened was in August 2003. At that time Earth and Mars happened to be unusually close even for a close opposition. In fact, they were the closest that they had been in 60,000 years (but only just barely so!). Mars was still tens of millions of miles away, though. Even so, it got a LOT of press attention.
Unfortunately, someone used some very ill chosen words to describe the event to a member of the press. Sadly, the reporter apparently knew next to nothing about astronomy, and so the quotation was butchered, and what the astronomer was cited as saying was not what he really said. What was said was that Mars would be so close to Earth, that a modest telescope operating at its highest power would make Mars appear as large in the telescope’s eyepiece as the Moon appears to the naked eye. In other words, Mars would appear to have an apparent angular size of about half a degree when viewed through the telescope. Mars is a small world, so that is pretty huge for Mars. However, the key point is that at high magnification Mars would appear through the telescope as if it were as large as the Moon to the naked eye. Actually, that was a really optimistic view on how high magnification could be realistically expected. Still, it was a dramatic statement. The reporter got it wrong, though, and said that Mars would appear to the naked eye as large as the Moon. That misstatement was widely reported. Soon, it started to make the email rounds, highly embellished. Well, Mars came, and went. We set up telescopes at the college and observed it. At best, Mars was about the size of some of the lunar craters, NOT the apparent size of the Moon!
The next year, 2004, Mars was not even visible. So, it was a surprise to me when I got an email forwarded to me from someone saying that Mars was going to be as big as the Full Moon on August 27 of that year! No, I explained to the person sending the email. This was an email from the year before, and it was wrong then, and even more so in 2004, since Mars was on the opposite side of the Sun in 2004! Then, in 2005, Mars was going to again be in opposition, but this time in November and quite a bit farther from Earth than it had been in 2003. Yet, once again, these emails were circulating in the summer of that year, claiming that Mars was going to be as big as the Full Moon on August 27! No, I told everyone. Then, last year, Mars was again on the far side of the Sun and not visible from Earth. Yet, once again, the email rumor came around. This time, someone had put together a really snazzy PowerPoint presentation about how Mars would appear the size of the Full Moon on August 27. The trouble was that it was WRONG. First of all, it was still the wrong data, and secondly Mars was not even visible in August 2006! So, now, the email rumor is once again recirculating. And, it is STILL wrong.
So, if any of you get this thing, don’t pass it along! It is totally wrong! Mars will be in opposition this year, but not August 27. Instead, Mars will be in opposition on December 24. Actually, the way that the orbits work, Mars will be closest to Earth about five days before opposition, on December 19. At that time, it will still be nearly 56 million miles away, much farther than the August 27, 2003, event.
So, whenever you get one of these urban legend Mars emails from a friend, gently tell them that they are in error, and feel free to point them to this posting, or my one from a year ago.
-Astroprof
Kelly on August 9, 2007 at 8:28 am: 1
Thank you, Astroprof! You’ve come through for me yet again.
A Ler…-- Rastos de Luz on August 10, 2007 at 5:44 am: 2
[…] Mars is Still Not Going to Appear as Big as the Moon no Astroprof’s Page […]
berry on August 10, 2007 at 5:29 pm: 3
i understand that the full moon is 1/2 a degree with the naked eye. how big is mars (in degrees) to the naked eye?
Astroprof on August 10, 2007 at 5:50 pm: 4
In 2003, Mars was about 20 arcseconds. That is about 0.0056 degrees, or about 1/360 the apparent size of the Moon. This December, it will be about 17 arcseconds, or 1/424 the apparent size of the Moon.
Dj Barabello on August 26, 2007 at 5:05 am: 5
December ?? Its on August 27 t night… and i think it will be about 63 arcsecond…..hope so
Astroprof on August 27, 2007 at 7:39 am: 6
No. It will be in December, 2007, and it won’t be 63 arcseconds this year.
Adam on August 27, 2007 at 10:28 pm: 7
im really disappointed. i mean im 13 and i was looking forward to this for months and now at 11:30 i find out it won’t happen. people are so immature to send around these messages just for laughs.
p.s. thank you Astroprof for the info so i dont stay up all night for nothing.
Mars Hoax of August 27 « The Sky Above on August 27, 2008 at 11:08 am: 8
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