How we have measured the distance of planets from earth to planet and planet to planet?
354744
This is a great question, actually, and one that bothered astronomers for centuries.  In short, there’s no simple way to measure the distances to planets—at least not without really good telescopes (and a bit of luck).\n\nIn the early 17th Century, Kepler devised his Third Law, which releated the distance of a planet from the Sun and the time it took to revolve around the Sun.  So if you know one interplanetary distance, you can figure out the rest.  Which is all well and good, except that there were no good distances at the time.  (A rough sense of the distance between the Sun and Earth constrained the numbers somewhat, but the estimates were pretty far off—Kepler thought the Solar Syatem was about one seventh its actual size.)\n\nThe first accurate means of determining the distances was by observing transits of Venus across the face of the Sun.  Through relatively simple trigonometry, one can calculate the actual distances between the Sun, Venus, and Earth.  Unfortunately, transits don’t occur very frequently, so it was only in the 19th Century that reasonable results were achieved.\n\nNowadays, the distances to planets are determined by bouncing radar off them.  Because we know how fast light travels, we can simply measure the time between emitting a radio pulse and its return back to Earth, which gives us the distance!  Easy as pie…\n\n(In the case of the Moon, we actually bounce lasers off a reflector left there by Apollo astronauts.  Because of the phase information of the laser light, we can get extremely accurate distances to our nearest neighbor.  That’s how we confirmed that the Moon is moving away from us at the rate of about 3.8 centimters per year.)\n\n\nRyan Wyatt\nRose Center for Earth & Space\nNew York, New York
35063
Both the Earth and Pluto orbit around the sun at different rates so their relative positions are constantly changing.  In addition, Pluto has an extremely eccentric orbit that at some times brings it closer to the sun than Neptune.  Using their orbital extremes and considering their positions around the sun, these are the closest and furthest distances between Earth and Pluto.\n\nClosest (Earth at furthest point from sun, Pluto at closest, both on same side of sun) - 4,284,726,912 kilometers (2,662,405,870 miles)\nFurthest(Earth at furthest point from sun, Pluto at furthest, both on opposite sides of sun) - 7,223,830,230 km (4,488,680,000 miles)
1005688
This is actually a difficult question to answer because the planets are moving in their orbits all the time, and so the distance from each planet to Earth is constantly changing. When both planets are on the same side of the Sun, and form a line with the Sun, then they are closest to each other. When two planets are on opposite sides of the Sun, and form a line with the Sun, then they are farthest away. For example, the planet Venus is about 42 million kilometers (26 million miles) from Earth at its closest point and about 258 million kilometers (160 million miles) away at its most distant point. \n\nUsually when people ask this question, what they mean is "What is the distance between the orbit of Earth and the orbit of each planet?" or "What is the closest that each planet comes to Earth?" (These are essentially the same question, right, because the planets can't get any closer than their orbital spacing allows.) You can compute this in a rough way by assuming that the orbits are circular, and looking at the planet-to-Sun distance for each planet. Since the distances are so large, we usually express them in Astronomical Units (AU). (An AU is the distance from Earth to the Sun, about 150 million kilometers or 93 million miles). The list below shows the distance of each planet from the Sun in AU. \n\nPlanet Distance from Sun in AU \nMercury 0.39 \nVenus 0.72 \nEarth 1.0 \nMars 1.5 \nJupiter 5.2 \nSaturn 9.5 \nUranus 19.2 \nNeptune 30.1 \nPluto 39.5 \n\nTo find the distance between the orbits of two planets in AU, subtract the two planet-Sun distances. For example, Earth orbits at 1 AU from the Sun and Venus orbits at 0.72 AU from the Sun. The difference between these two distances is 1 - 0.72 = 0.28 AU. To get the number in kilometers, multiply by the conversion above: 0.28 x 150 = 42 million kilometers. \n\nThe numbers above are generally what's used in introductory astronomy classes.
46875
Approximately 93,000,000 miles.  The distance varies because our orbit is not perfectly circular.
220002
its done by counting how long it takes for light from the planet takes reach here. usually between a period of dark and light. same as the sun
262422
Time is a measurement of movement through space. The earth rotates around the sun once = one year, the earth completing one spin on it's axis = one day, etc...\n\nFor measuring distances in space we use light years (the time it takes for light to go from point a to b) instead of miles because the distances are so great. Example: If we look at the closest star in the night sky, it's about 4 light years away. That means it's measured by how long that star's light takes to reach our eyes. So we are really looking at how the star looked 4 years ago, not now. If that star exploded 2 years ago, we would still see it for another 2 years and then we see it explode.
1163913
The average distance between the Earth and the Sun is 149,590,787 km or 92,951,640 mi. This distance is called an Astronomical Unit (AU). The orbit of the Earth deviates a bit from a circle, so the distance between the Earth and the Sun isn't always the same. The Earth is closest to the Sun (in the perihelion of the Earth's orbit) around 4 January, when it is winter in the northern hemisphere of the Earth and summer in the southern hemisphere, and is furthest from the Sun (in the aphelion of the Earth's orbit) around 4 July, when it is summer in the north and winter in the south.\n\nThe difference between the distances on 4 January and 4 July is about 3 percent, which corresponds to about 5 million km or 3 million mi.
899300
The distances to stars closer than about 150 light years can be measured directly by use of parallax.  The position of the star against background stars is measured at times 1/2 year apart, and then it is a simple mathematical procedure to determine the distance (you have a side and two angles of a triangle--the angular distance the star appears to move at it's distance over 1/2 year equals 186 million miles-the diameter of the orbit of the earth).  \n\nStars farther than that cannot be measured directly.  But, by use of knowledge about how bright a star should be (on average) for it's spectral type (which loosely is governed by its mass) an estimate of its intrinsic brightness can be made, and then by looking at how bright it appears, it's distance can be estimated.\n\nCepheid variables are used, as well, but mostly to determine the distances to groups of stars and of other galaxies.  Incidentally, the North Star (Polaris, or Alpha Ursa Minor) is a cepheid variable.\n\nNovae and supernovae tend to have average intrinsic brightnesses, so their apparent brightness in, say, a distant galaxy, tells us (within limits) it's distance.\n\nRed shift is used for objects outside our galaxy because the amount of red shift within our galaxy would be extremely small (it increases with distance) if it were not totally overcome by the gravity of the galaxy.
606341
It depends on whether you are talking about a planet in our solar system or an extra solar planet. I'll describe both.\n\nFor a planet in our solar system, the apparent size can be directly measured optically. One way is to take a picture of the planet through the telescope and measure the size of the picture with a ruler. Calculations based on the focal length of the telescope will tell you how many degrees (or fractions of a degree, since it will be less than 1) wide the planet appears to be in the sky for a given measured size on the photograph. Then the distance to the planet must be measured, which is not so easy. Basically it comes from triangulation to nearby asteroids combined with kepler's laws. Knowing the distance and apparent size allows you to calculate the real size and volume. To get the density, you need to know the mass. If the planet has Moons, the orbital period of the moons gives you the planet's mass from orbital mechanics calculations. If the planet has no moon, like Mercury and Venus, then theoretically their mass can be gotten from the effect their gravity has on the orbits of other planets, asteroids and comets, but this is not so accurate since those other objects don't usually pass close enough to the planet we want to measure to show much of an effect on their orbits. Fortunately we have sent space craft to Mercury and Venus and measured their mass directly by the effect their gravity had on the space craft's path.\n\nFor a planet orbiting another star, it is not so easy, because such planets cannot even be seen. Their presence is deduced from tiny Doppler shifts of the star they orbit. A planet does not just orbit a star, the star and planet orbit each other around their common center of gravity. Since the star is much heavier than the planet, it doesn't move much, but it does move, and modern instruments can measure the tiny Doppler shift in the star's light to get the motion of the star. Stellar evolution models tell us how heavy the star is and orbital mechanics tell us how heavy the planet is. (We can calculate the mass of double stars using orbital mechanics and the Doppler shift of each star's light, but we have no direct knowledge of the mass of single stars.) If the planet also happens to orbit in a plane parallel to our line of site, it will cross directly in front of the star once each orbit, like Venus sometimes crosses the face of our sun as seen from Earth. When it does, it blocks a small percentage of the star's light and the star looks slightly dimmer. If the star dims by 1%, then the disk of the planet has 1% the area of the disk of the star. Again, from stellar evolution models, we can deduce the diameter of the star and so get the diameter of the planet. (We can measure the diameter of some large, nearby stars, directly with the largest telescopes and adaptive optics, but for most stars we have no direct knowledge of their diameter.)\n\nThere is much more detail, but enough is enough, don't you think?
278569
The previous answerer gave one method that was actually used in antiquity and gave a very good answer. Other methods involved looking at the horizon from the top of a mountain and trying to measure the angle down to the horizon from a level. That can be used to figure out the size of the earth, but the angle tends to be too small to give much accuracy. Many scholars in the 15th century, though relied on this figure more than the one done by the stick method (which was much more accurate). This is part of why they thought the earth was so much smaller than it really is.
931645
first answer was close to right.\n\nthere is one qualification that seems need.\n(do this all in meters for easyness of calculation)\n\nR = radius of earth = 6400 km = 6.4 * 10^6 meters\nd = distance to horizon in meters\nh = height in meters\n\nSimilar triangles:\n\nR / d  = d / 2h\n\nd^2 = 2Rh\n\nd = sqrt (2Rh)\n\n....  works pretty well for small "h"\n\neg 2 meters height =>\n\nd = sqrt (2 * 6.4 * 10^6 * 2 ) = sqrt (25.6 * 10^6) \n=5.06 km\n\n[[ online calculator gives 5.5 km ]\n\nmine's a LOT easier to use ...\n\nI use "2h" instead of "h" for similar triangles\nbecause of discrepancy of right angle at the\nradius from eearth-center to observer and\nr-a from earth-center to distant object.\n[intersection happens "h" below earth surface]\n\nthat sounds confusing but I can't draw a picture\n\nmy eqn is easiest possible tho ..
935938
They have used the paralax method since about that time.  This is measuring the arc of items in space with known distances.  They have known diamater of the earths rotation 186,000,000 for a long time.  Knowing that it is possible to measure the distance of astronomical items using one second of angle in the difference of an items location in the sky measured six months apart.\nB
118502
At that rate, it'd take about 2 trillion years for the earth to reach the distance from the sun where Venus is.  The solar system is only about 4 or 5 billion years old.  Answer: Venus was almost certainly never where we are.
66810
Earth ranges from 7,926 miles to 7900 miles, depending on your location.\n\nThis is approximately 12,756km
221827
by using the speed of light. As the Sun emits the light, it takes time to reach Earth. The speed and time taken is calculated to get the distance between the two. It takes about 7 minutes for the light to reach Earth. So looking at the sun from Earth is looking at the Sun 7 minutes ago!
396604
dr_islam_safwat is exactly correct, as far as he goes. The problem is that Kepler's 3rd law does not tell you how far Neptune is from the Sun, it only tells you how much farther from the Sun it is than the Earth. The real trick to to find out how far the Earth is from the Sun. Actually, knowing the absolute between any two planets would be enough information, because then Kepler's 3rd law could then be used to find all the other absolute distances from the ratios.
218700
Do mean "difference" or "distance"?\n\nIf it's difference, well, Venus is the 2nd planet from the sun, Mars is the 4th planet from the sun, and Jupiter is the 5th planet from the sun.\n\nVenus is a rocky planet just slightly smaller than earth with a hot, dense, atmosphere.\nMars is a rocky planet just over half the diameter of earth with a cold, atmosphere with a pressure of about 1/10 that of earth.\nJupiter is a gas giant that could contain many earths.\n\nI'm guessing that your question has more to do with the distances between the orbits of the planets rather than the actual distances between the planets because the distance between the planets can vary greatly depending on where each is it's orbit.\n\nThe site linke below has the distances in astronomical units and kilometers (km) from the sun for the orbits of each planet.  Maybe from that you can figure out the answer to your question.