No, Mars will not appear the size of the full moon on 27th August!

Every year since 2003 I have been sent this e-mail;

Two moons on 27th August
27th Aug the Whole World is waiting for………….
Planet Mars will be the brightest in the night sky starting August. It will look as large as the full moon to the naked eye. This will cultivate on Aug. 27 when Mars comes within 34.65M miles off earth. Be sure to watch the sky on Aug. 27 12:30 am. It will look like the earth has 2 moons. The next time Mars may come this close is in 2287. Share this with your friends as NO ONE ALIVE TODAY will ever see it again.

Firstly, they probably mean “culminate” and not “cultivate”.

This e-mail started circulating in 2003 when Mars DID make a spectacularly close approach to Earth, the red planet came within 56 million kilometers of us. This was the closest approach for almost 60’000 years. Although Mars’ 2003 approach was particularly close, the planet did not appear particularly larger or closer than it does every 15 to 17 years during it’s regular perihelic opposition.

Now, lets get on to the fun part, how close to Earth would Mars have to be in order for it to appear as large as the full moon?

The equatorial radius of the moon is 1’738.14 km, which makes its diameter (2xr) 3’476.28km. At perigee (closest approach) the moon is a distance of 363’104km.

The equatorial radius of Mars is 3’396.2km, which makes its diameter 6’792.4km.

For mars to appear the same size as the full moon, based simply on the measurements of the diameters of the two bodies, mars would have to be approx. 720’000km from earth. My reasoning here is that if the planet Mars has a diameter of approx. two times that of the moon, it would have to be approx. twice as far from Earth in order to appear the same size as the full moon.

Seven Hundred And Twenty Thousand Kilometers! Not FIFTY SIX MILLION kilometers. Seven hundred and twenty thousand. That is a factor of 77,77 times closer than the planet will be at it’s closest approach in sixty thousand years.


Case Closed.


7 responses to “No, Mars will not appear the size of the full moon on 27th August!

  1. Pingback: Will Aderoid be our second sun this June? « The Skeptic Detective·

  2. Dear Angela,

    A great post with great maths.

    The Johannesburg Planetarium have a nice diagram for those that still don’t understand the maths. In the meantime, we could start selling T-Shirts as the urban legend is now spreading fast!!!

    Quick, buy canned food now. You wont need candles, Mars would provide the light.

  3. Pingback: It’s my first birthday! « The Skeptic Detective·

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s