i would like to know why it took so long to discover uranus and neptune?

Question

what physical principle was neptune and uranus a key test for?

Answer 1

Uranus and Neptune are both so far away that they are too faint to be seen. Uranus is just barely a naked eye object under ideal dark sky conditions, and Neptune is too faint to be seen with the unaided eye. They are also so far away that even through a telescope they are not easy to identify. Uranus is a tiny blue spot, and Neptune is a tinier blue spot, and that's through a large telescope.

William Herschel found Uranus with his telescope in the 1700s. Uranus, being so far from the sun, takes 84 years to complete one orbit, so it took some time for them to make sufficient observations to predict its orbit, and then further observations that showed it was not following the prediction. Having postulated a further planet perturbing the orbit, a search was begun and Neptune was found, very close to where the calculations predicted, in 1846.

Galileo had observed Neptune in the 1600s, but his telescope could not resolve it as a disc, and due to a case of bad timing it just so happened to be beginning its retrograde motion, the time when the planet seems to stand still and then reverse its movement across the sky as Earth overtakes it in its orbit. With no ability to see it as anything other than a point of light and with it being apparently stationary, Galileo could not have supposed he was looking at another planet.

So, it took so long to find them because they are invisible without optical instruments, require great magnification to resolve as anything but star-like points of light, and move across the sky slowly enough that repeated observation of the same area over some time is needed to detect their movement. Not until suitable technology was available could they be found and identified for what they are.

Answer 2

Uranus is very faint, and with the naked eye (what most astronomers used prior to the 1500's), it went undetected. Once it was discovered, and Kepler's laws were put into play, they found that it didn't behave quite the way it should - that there was some other force responsible for slowing Uranus down.... And that's how they discovered Neptune. In fact, they had calculated Neptune's mass and approximate location before actually seeing it.

Answer 3

They are very far, and almost impossible to see with the Naked eye.

As times changed, and technologies became better, us humans build more powerful telescopes, and could discover these new planets.

If you think about it, we are now discovering planets OUT SIDE the Solar system.

When my dad was born this had never happened, and it took new technologies forthis to happen.

Answer 4

We just needed better telescopes than available prior to their discovery

Answer 5

it does not reflect too much light so it was hard to see using the kind of telescopes back then.

Answer 6

They're further away, and they didnt have strong enough telescopes.

Answer 7

Technology or the lack of it in this case.

Answer 8

Because they are really really far away.