In 2007 an email was
widely circulated which claimed that on
This is nonsense. It is probably a hoax, though what the motivation is for it I cannot guess. The same hoax circulated in 2005 and 2006. Whoever perpetrates this misinformation cannot even get the year right, as the event to which it refers actually happened several years ago, although Mars certainly did not (and will not, and cannot) appear as large as the Moon.
In August 2003 time Mars
was indeed (marginally) closer to the Earth than it had been for thousands of
years, being about 34.6 million miles from the Earth. It was given a lot of publicity at the time;
we had open evenings at the Guernsey Observatory to view Mars. Its angular size then was 25 arc-seconds,
compared with the Moon’s 30 arc-minutes.
In other words, Mars appeared one-75th of the angular diameter of the
Moon. That is about as large as we ever
see Mars, and occurs when Mars is at ‘opposition’, ie on the same side of the
Sun as the Earth is. The Earth moves
faster than Mars in its orbit around the Sun, and so regularly overtakes Mars,
with over two years between each of these oppositions. The last opposition of Mars took place on
On
This “hoax” may, of course be someone's totally mistaken interpretation of angular diameter, although the fact that it is perpetrated year after year implies a mischievous intent. It is possible that someone originally has confused arc-seconds (1/3600 degree) with arc-minutes (1/60 degree). It has also been suggested that it arises because of the omission of the fact that to magnify the angular diameter of Mars to that of the Moon in August 2003 would have required a telescope and (in 2003) a 75-magnification eyepiece.
However, common sense and simple mathematics shows that Mars (diameter 6794, closest distance 55 million km) must appear much smaller than the Moon (diameter 3476 km, average distance 384,400 km)!
There is a number of web sites explaining this hoax. For example, see:
© David Le Conte, August 2007 (revised January 2008)