On August 27, 2013, the moon and Mars will appear to be the same size to the naked eye. That's how the story goes.
I first heard about this when a friend sent it out and said: "Don't know how true this is. Can anyone explain to me?"
So I promptly emailed Aaron Turner, our resident astronomy expert and blogger on Patch.
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"I was waiting for this to come up yet again. We, in the astronomical world, call this the 'Mars Hoax.' It all started in 2003.
Here is the full story behind this.
The distance between Earth and Mars varies dramatically over time. The maximum distance (when Earth and Mars are on opposite sides of the Sun) is about 250 million miles, and the minimum distance (Earth and Mars on the same side of the Sun, with Earth at its farthest distance from the Sun and Mars at its closest distance, is 33 million miles.
As a result, the apparent size of Mars does vary quite a bit, from a mere speck when seen through a typical telescope, to a small disk.
When Mars is at its closest approach, the disk shows some level of detail of the surface of the planet, including large canyons and mountain ranges, though typically still quite blurry when viewed by eye through an amateur's telescope.
Mars comes within [approximately] 50 million miles of Earth once every 18 months or so. Because the orbit of Mars is more elliptical than Earth's orbit, it does occasionally get within 35 million miles, and the time between such closer approaches is measured in thousands of years.
The last closest approach occured on August 27, 2003 at 12:30 a.m.
A couple months before that closest approach, some astronomer posted a PowerPoint presentation discussing the event on the Internet.
This presentation was completely accurate in what it said, though not particularly well organized or detailed.
In the slides, a comparison was made to indicate how large Mars would appear when viewed through a typical (amateur) telescope.
The statement read: "at a modest 75 power magnification..., Mars will look as large as the full Moon to the naked eye."
What was meant was that it would appear as large as the full Moon appears when the full Moon is viewed without a telescope.
Without getting into a debate about whether such a comparison makes sense at all, I will say that this is approximately correct.
However, in the final posted presentation, the statement "at a modest 75 power magnification..." appeared at the bottom of one slide, and the statement "Mars will look as large as the full Moon to the naked eye" appeared on the next slide.
The presentation itself was viewed by a handful of people, one of whom republished it as a simple text email, but left in a line break between those two parts of the key sentence.
Elsewhere in the presentation and in the email, the closest approach date is mentioned as August 27th, and the time at which Mars reaches the highest point in the sky as 12:30 a.m.
It is also mentioned that the next time Mars will be this close to Earth is in the year 2287, and, in big bold letters, "NO ONE ALIVE TODAY WILL EVER SEE THIS AGAIN".
That email was then sent out and copied to millions of people, with most of the other parts of the text removed.
As a result, every July and August since 2003, we see a recurrence of these emails or other Internet message types, carrying the same message.
I have received either the email, or a question about this almost every year since 2003.
In fact, three years ago it was my mother who asked me about this and enthusiastically reported that she would be staying up to see this once-in-a-lifetime event. Meanwhile, Mars isn't even visible in our nighttime sky this year (or in most of the years since 2003)."
So there you have it - the Mars Hoax. If you'd like to read more from Aaron Turner, click here to visit his astronomy blog:
(Photo by Aaron Turner)