Apparent size distance and same distance view question

papiamento · Post by **papiamento** » Wed Nov 09, 2005 2:50 am

I was thinking about the Mars hoax and that got me thinking about two interesting (possibly APOD) ideas.

First - how far would each of the planets have to be from Earth to appear the size of the full moon.

Second - what would the sky look like if they were the distance to the moon. I know that the outer diameter of the rings of Saturn are about equal to the Earth-Moon distance - roughly. As is approximately the Io-Jupiter distance. Probably with Jupiter and Saturn, the entire sky would be taken up in this exercise.

As in, how much of the sky would be taken up if each of the other 8 planets were 250,000 miles away.

Anyone want to take a whack at this one?

craterchains · Post by **craterchains** » Wed Nov 09, 2005 2:53 am

Just watch the Star Wars movies instead.

papiamento · Post by **papiamento** » Wed Nov 09, 2005 3:02 am

Haven't since Return of the Jedi. Sorry.

But let's talk starquakes and AXPs and SGRs and I might be interested.

craterchains · Post by **craterchains** » Wed Nov 09, 2005 3:05 am

Star Wars III drags a bit, but worth the scenery CGI stuff.

And I thought you wanted to talk about Mar's hoaxes?

orin stepanek · Post by **orin stepanek** » Wed Nov 09, 2005 3:09 am

Since Mars is twice the diameter of the moon; it would have to be twice the distance to appear the same size as the full moon. You could research all planets accordingly. I don't think I would like such a cluttered sky.
Orin

S. Bilderback · Post by **S. Bilderback** » Wed Nov 09, 2005 12:59 pm

Sorry, it is not a linier equation. The Moon covers on average 2 degrees of arc (or is ir 0.5?). If Mars was at the same distance as the Moon it would measure 4 degrees - that would be a linier measurement. For the distances of the rest of the planets to equal 2 degrees arc, the equation would have the factor Pi involved.

makc · Post by **makc** » Wed Nov 09, 2005 2:49 pm

S. Bilderback wrote:Sorry, it is not a linier equation.

yes it is. here, I've made a scketch:

craterchains · Post by **craterchains** » Wed Nov 09, 2005 2:56 pm

I think yer both right.

Sorry, I just coundn't help myself.

Norval

orin stepanek · Post by **orin stepanek** » Wed Nov 09, 2005 7:34 pm

I made a diagram at home like makc's because I was sure I was right and I started having doubts. I even took it to three times the distance and the ratio stayed the same. I don't really understand the degrees of arc concept.
Orin

S. Bilderback · Post by **S. Bilderback** » Thu Nov 10, 2005 1:01 am

You are absolutely right, it is a linier equation - I stand corrected - thanks.

The 0.5 degrees of arc (it's not 2 degrees) is simply there is 360 degrees of viewing angles and a Full Moon will cover 0.5 degrees of the 360.

papiamento · Post by **papiamento** » Thu Nov 10, 2005 2:16 am

So the diameter of the other planet divided by the diameter of the moon times the earth moon distance gives us the distance that planet would have to be to appear the size of the full moon. Did I phrase that correctly? If that aren't any other wonky factors, i can do the research and crank out my answer.

The second question as to what the sky would look like if any of the other planets were the earth-moon distance away is still an intriquing one visually.

S. Bilderback · Post by **S. Bilderback** » Thu Nov 10, 2005 3:52 am

Consider yourself lucky; some might say by definition the Earth and the Moon are a binary planet system. Mercury and Venus don't have any moons, on Mars the moons are hardly noticeable, and by size comparison the gas giants' moons would be equally unnoticeable. It is so dark near Pluto, nothing would be interestingly visible anyway the most visible part of the moon(s) would be them eclipsing light sources.

In a way, you have your wish - enjoy it.

papiamento · Post by **papiamento** » Thu Nov 10, 2005 10:43 am

No, you misunderstood my question. What would OUR sky look like if these planets were if those planets were at the moon's distance - which would include the sun's illumination of them as well.

papiamento · Post by **papiamento** » Thu Nov 10, 2005 10:44 am

Oops - sorry, I stuttered (these planets, those planets)

(I just woke up)

S. Bilderback · Post by **S. Bilderback** » Thu Nov 10, 2005 12:54 pm

Think of how bright the "Moon Shine" would be at nigh if Jupiter was a the Moon's distance . . .

. . . Wait, that would make the Earth a moon of Jupiter and we would be fried by its radiation field - yiiiiiiiiiiks!

BMAONE23 · Post by **BMAONE23** » Thu Nov 10, 2005 2:52 pm

Consider this, Jupiter would just fit between Earth and the Moon. If either of the gas giants were the moons distance away, (and we were moving fast enough for a stable orbit), they would fill the field of view. If saturn were placed between the Earth and Moon, the ring system would disappear in one orbit and earth, crater wise, would look like the moon.

papiamento · Post by **papiamento** » Fri Nov 11, 2005 1:47 am

well there's a "boy howdy!" - I guess we would clear the ring systems -
wouldn't we?

let it snow, let it snow, let it snow

S. Bilderback · Post by **S. Bilderback** » Fri Nov 11, 2005 1:53 am

It would be cool if Saturn was about where Mars is, that would delight in the evening sky. By a quick guesstimation, Saturn (without rings) would appear about the size of the Moon.

Starship Asterisk*

Apparent size distance and same distance view question

Apparent size distance and same distance view question

Star Wars instead, huh?

Distance Question revisited