How can know there are galaxies trillions of miles away but cannot get a picture of the flag on the moon?

Answer 1

That is like saying "why can a I see a mountain 20 miles away, but I can't see a speck of dust 5 feet away"

Answer 2

But we CAN get a picture of the flag on the moon!  The only problem is, the picture includes so much moon that it's impossible to pick out the parts that are flag.

We see remote galaxies because they are glowing (and radio-emitting, and sometimes gamma- and xray-emitting) objects seen against a dark background.  This is crucial; if there was a lot of interference from other objects, you wouldn't be able to see them.  We can't see distant galaxies behind nebulae or even dense star fields, so the same thing applies.

The angular width of a 3' wide flag on the moon seen from the Earth is about 0.5 milli-arcsecond.  This sort of resolution can be achieved with radiotelescope arrays, but not with optical telescopes.  An optical telescope is limited to roughly 1 arcsecond resolution, and even the Keck interferometer can only achieve about 5 milli-arcseconds.  From Earth, the smallest spot on the moon you could distinguish from other spots would be about 30 feet wide even if you used the Keck interferometer.

Now if you put that flag in orbit, you'd be able to see it just fine!

Answer 3

The flag on the Moon is not a light source that emits a powerful beam of light. It is also very small compared to its distance from Earth. Figure that the flag is on a pole six feet high. And, the Moon is 240,000 Miles away. That distance is ten times the circumfrence of the Earth. No telescope ever made can do that.

The reason we can see constellations of stars millions of light years away is that within those galaxies are brilliant stars just like or even bigger than our Sun which give of abundant light energy. We are seeing the light energy from them, not the objects themselves.

Answer 4

Diameter of flag left on Moon 0.3 metres. Distance to Moon, 384,000 kilometres. Diameter of flag as a ratio to distance is therefore no more than 1 in almost 1280 million.

Diameter of Andromeda galaxy is about 220,000 light years. Distance of galaxy is just less than 4 million light years Ratio of diameter to distance is more than 1 in 20.

The furthest galaxies yet detected are 13 billion light years away. If they are the size of Andromeda the ratio of diameter to distance is like 1 in 60,000 which is still a lot bigger than 1 in 1280 million. At that distance though these galaxies are little more than spots.

Answer 5

Because galaxies are trillions of miles wide. While the flag on the moon is only a few feet. One light year is roughly 5.8 trillion miles. Even the smallest galaxies are 4000 light years in size. Thats about 23,200,000,000,000,000 miles in size.

Answer 6

The flag is tiny, galaxies are huge. The apparent size of the various objects in the sky is given in degrees, minutes and seconds of arc. 60 seconds make one minute, sixty minutes make one degree, and 360 degrees make a complete circle around the sky. The Moon, as an example, subtends an angle of about 30 minutes of arc.

The flag measures about a metre across. Using trigonometry you can calculate that at a distance of 400,000km, the distance from Earth to the Moon, this would subtend an angle of 0.00052 seconds of arc, way too small to be resolved by any earth-based optical instrument.

Galaxies vary in size, but let's take our own galaxy as a typical example. It's 100,000 light years across. The furthest object observed so far is about 13,000,000,000 light years away. So, using trigonometry again a 100,000 light year diameter galaxy located 13,000,000,000 light years away subtends an angle of about 15.9 seconds of arc, only 1/113 the apparent size of the Moon, but over 31,000 times wider than the flag appears. That's an extreme example. Many galaxies and nebulae are considerably closer than that, and therefore appear correspondingly larger. Because they are so faint we can't see them with the unaided eye and need optical instruments like the Hubble telescope to see them. Telecopes are used not only to show things that are too small to be seen, but also things that are large but too faint to be seen.

So, the flag is close but tiny, while galaxies are distant but vast.

Answer 7

The answer has to do with the laws of optics (resolution). The area of a flag is at max what? 3 feet by 5 feet! A galaxy is perhaps 100,000 or more light years across.

Answer 8

Basically because galaxies are a whole lot bigger than the flag.

The best optical telescopes have a resolution of about 0.2 seconds of arc. At the distance of the Moon, this corresponds to about 100 meters, or the size of a football field. At the distance of the nearest galaxies, this corresponds to around a lightyear---but the galaxies are over 10,000 lightyears across.

Answer 9

possibly it's a problem of angles. the moon rotates at just the right speed so that the same side is always facing earth (it's seriously freaky). I'm not sure where exactly on the moon the flag was planted, but if it's on the far side, we'd never been able to see it directly from earth or from earth orbiting satelites. If it's close enough to the center of that earth-facing side, then it would basicly be pointing straight at us (or close enough to it) that there's really nothing to see from our "top-down" view.


The other possiblilty is that nasa faked the whole thing so there is no flag to see.

Answer 10

We don't actually take pictures of these galaxies, but pretty much guess and calculate that they must be there based on star movements, gravity, etc. Telescopes pick up stars as dots, when effectively most of them are bigger than our sun.