What Would It Look Like If Mars, Saturn Or Neptune Replaced The Moon?

The becomes part of the figure of the Winter Hexagon this evening. Most of the brightest stars of the winter sky form the hexagon with the exception of Orion’s Betelgeuse, which gets stuck in the middle of the figure.  The map shows the sky facing southeast around 8 o’clock local time. Created with Stellarium

Tonight the nearly full moon will become part of the Winter Hexagon, one of the biggest and easiest to see asterisms of the winter sky. You’ll find Luna twixt Procyon in Canis Minor and Pollux in Gemini along the eastern side of the figure which is comprised of six bright stars. When connected by imaginary lines, the stars form a hexagon 65° tall by 45° wide that reaches from the zenith to low in the southern sky.

Saturn at the moon’s distance from Earth rises majestically above the skyline. Appearing more than 33 times larger than the moon, its globe is 16.5° across while the rings extend nearly 40° from end to end or more than twice the size of the constellation Orion. Credit: Roscosmos

The moon’s 240,000 miles from Earth and 2,160 miles (3,475 km) in diameter. To get there by foot would take you 9 years. Seen from Earth, the lunar sphere spans just 1/2° of sky – you can more than cover it up with the tip of your pinkie finger.

At 7,500 miles across, Venus is only a few hundred miles smaller than Earth. It would appear very white and bright and just under 1.75° across or just shy of 4 times larger than the moon. Credit: Roscosmos

Yesterday we replaced the Sun with Polaris, Vega, Sirius, Alpha Centauri and Arcturus to get a feel for the real dimensions and appearance of what are otherwise tiny twinkling points of light.

Today we’ll replace the moon with several of the planets to better appreciate their true dimensions. Like the stars, all the planets look like dots of light to the unaided eye.

At 4,212 miles across, Mars is only about twice the size of the moon and would be 1° across. Your pinkie would just cover it. Credit: Roscosmos
Wouldn’t it be nice to just walk outside and see Jupiter’s Great Red Spot and all the wild weather happening within its many cloud belts? At the moon’s distance, all you’d have to do is look up on a clear day. Jupiter’s so big Earth would become another of its moons. We’d also be bathed in its dangerous radiation environment. Credit: Roscosmos
Uranus is four times the size of Earth and would appear a pale blue color in our sky. Credit: Roscosmos
Neptune’s deeper shade of blue is caused by methane gas in its atmosphere which absorbs light of longer wavelengths (yellow, orange and red). Neptune’s about 1,000 miles smaller than Uranus. Credit: Roscosmos
Covered in craters and just 1.5 times the size of the moon, Mercury would appear similar to our own satellite in the sky. Credit: Roscosmos
Now this looks weird. Earth in Earth’s sky? Of course this is how big the Earth would appear from the moon – 1.8° across or just shy of four times the size of the full moon. Credit: Roscosmos

And now for the video:

7 Responses

  1. Edward M. Boll

    I suppose that having Jupiter or another large planet that close could wreck havoc on our planet. I am thankful it is what it is. I just noticed on an internet blog that 2012 Pansataars K1 is not only getting faint it is getting out of view in a dark sky, close to the Horizon.

  2. NORMAN S.

    Hey Bob, when I was a kid, I had a startling dream where I stepped out into the back yard in the middle of the night and clearly visible were things like Saturn, spiral galaxies, etc., huge in the dark sky. Rather like these images. That dream has stuck with me in a vague way for fifty-some years. Norman

    1. astrobob

      That is a wonderful dream to have and hold onto. My favorite dream is where I start walking, jump and then begin to fly.

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