Mars as big as the full Moon on August 27 ?

Mars as big as the full Moon on August 27 ?
Will Mars look as big as the full Moon on August 27? (NO.)

Social media present an exciting story about two moons in the sky. The second “moon” would be Mars, seemingly the same size as the full Moon! One Facebook meme in August 2020 said:

12:30 Aug 27th you will see two moons in the sky, but only one will be the moon. The other will be Mars. It won't happen again until 2287. No one alive today has ever witnessed this happening.

Is this likely?

Mars vs the Moon
If we could view Mars and the Moon side by side, Mars would look four times bigger than the Moon. In actuality, the planet is over 200 times farther away than the Moon and looks like a reddish star. Although it would take Elon Musk 6-8 months to get to Mars, Neil Armstrong got to the Moon in about 3 days. But could Mars sometimes get really close to us?

Earth and Mars
Here is a diagram of the orbits of Earth and Mars. When the two planets are in the positions shown, they are relatively close to each other. About every 26 months, Mars, the Earth and the Sun are in a straight line. As the Sun rises in the east, Mars is setting in the west. Since they're on opposite sides of the sky, this is called an opposition.

The two planets are closest to each other around opposition, but the distance varies. It may be from around 56 million km (35 million mi) to 100 million km (63 million mi). But they can be an even more considerable distance apart. If they're lined up on opposite sides of the Sun, it's called a conjunction. If Earth were in the position shown in the diagram and Mars were at aphelion, its greatest distance from the Sun, they could be over 400 million km (250 million mi) apart.

How close would Mars have to be to look the same size as the Moon?
Since Mars is four times the size of the Moon, it would need to be four times the Moon's distance to appear the same size. That would be around 1.5 million km (940,000 mi).

Now consider these numbers. Around 60,000 years ago a close opposition brought the red planet to 54.6 million km (33.9 million mi) from Earth. At the closest approach in recorded history since then – on August 27, 2003 – Mars and Earth were 55.76 million km (34.65 million mi) apart. The next time that Mars is closer than that will be on August 28, 2287.

Even in the closest oppositions Mars is still over 40 times farther away from us than it needs to be in order to appear the same size as the Moon. Mars looks like a reddish star. As it nears opposition, it appears somewhat bigger and brighter, but it still looks like a reddish star. If it were going to look the size of the Moon, it would be looking quite large early on and continue to do so long afterwards.

In the closest opposition since 2003, July 2018 brought Mars to 57.6 million km (35.8 million mi) from us. The opposition was accompanied by a total lunar eclipse as seen in this photo taken in Rio de Janeiro. [Credit: Carlos 'Kiko' Fairbairn]

So how did the story of the two moons come about?
The 2003 opposition was a widely publicized event. One account, sometimes titled "Mars Spectacular", had circulated with useful information, including this snippet:

The next time Mars may come this close is in 2287. … At a modest 75-power magnification Mars will look as large as the full moon to the naked eye. … NO ONE ALIVE TODAY WILL EVER SEE THIS AGAIN

This said how Mars would look enlarged in a telescope. However, as the account made its way around the internet, it ended up losing part of an important sentence. As a result, it read “Mars will look as large as the full moon”. It's been reappearing ever since then, always with the key phrase missing.

Somewhere in the intervening years the the twin moons over the neoclassical Nilov Monastery in Russia was added to the meme - it's shown in the header image.

Oppositions don't occur on the same date each time. (In 2020 opposition is on October 6.) Yet the date given is always August 27 – even in a year without an opposition with Mars on the far side of the Sun in August.

No one alive today has ever witnessed this
This at least is true. It would be a magnificent sight, but it hasn't ever happened. And it won't ever happen.



You Should Also Read:
Mars Myths – Would You Believe Them
Absolute Beginners – Seeing Mars and Beyond
Lunar Eclipses

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