how is the earths radius, the distance to the moon, and the sun used to reckon distance to other stars?
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The only one of these used is the distance of the Earth to the Sun, which I believe is called a parsec. The more scientific method of measurring distance in outer space is the light year, which is the distance light travels in a year. Even this measure is small and most distances of galaxies are measurred in billions of light years.
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There are three basic methods:\n\n1. Parallax. The angle at which the object appears in the sky is very precisely measured at one point in the Earth's orbit, then measured again six months later. Since the Earth is in a different position at these times (186 million miles between the two measurments), the star will appear at slightly different angles, and its distance can then be worked out from these angles using simple trigonometry.\n\n2. Standard candles. Certain types of stars (Cepheid variables, RR lyrae variables), and certain types of stellar events (type Ia supernovae), have luminosities that can be worked out fairly precisely from their intrinsic properties (the variable stars for instance, have a period of variablility that is closely correlated with their luminosity, and the type Ia's luminosity can be worked out by examining its light curve). Since percieved luminosity varies inversely with the square of the distance, and since we konw how much light they put out at the source, we can work out how far away these stars are simply by measuring how bright they are.\n\n3. Redshift. The universe is expanding, and that means that from our perspective, distant galaxies are all moving away from us. This means that the light we recieve from them will be at a lower frequency (that is, redder) than the light they emitted, due to the doppler effect. Edwin hubble discovered that at large scales, the observed redshift is directly proportional to the distance of the object from us. This means that if the object is too far away to measure using parallax and lacks a good standard candle, we can still determine its distance simply by measuring its velocity. Actually doing this is somewhat difficult, and involves looking for patterns in the absorption lines in the object's spectrum to figure out what elements created those lines, and then one you know that you can figure out what the frequency of the light should be. After that, you have to work to filter out as many extraneous sources of redshift as possible, such as the object's gravity, its velocity due to gravitational interactions with other nearby objects (what is called the peculiar velocity), and so forth, to leave just the velocity due to the expansion of the universe - from which the distance is estimated using hubble's law.
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About 93 million miles away from the sun, give or take...about the same as earth, since the moon orbits the earth.\n\nIf you mean, what is the APPARENT position of the moon in relation to the sun, as seen from earth, it varies all the time, from 0 degrees (as during a solar eclipse) to 180 degrees (a lunar eclipse).
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"Astronomers can use parallax to find distances to objects much farther even than planets. To calculate the distance to a star, astronomers observe it from different places along Earth's orbit around the Sun. If they measure the object's position several months apart, their "two eyes" will have a separation of well over 100 million miles! \n\nNow astronomers have technologies to measure distances to other planets more directly. When we have a spacecraft at another planet, we know the time it takes a radio signal to travel between Earth and the spacecraft. We can also send a powerful radar signal toward a planet and time how long it takes for the echo to return. Astronomers know how fast these signals travel (the speed of light), so measuring how long they take makes it easy to calculate the distance very accurately."
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What is the circumference of the Earth? How far around is the Earth?\n\nThe average radius of the Earth is 3,959 miles (6,374 kilometers).\nThe equitorial diameter of the Earth (distance from one side of the Earth to the other at the equator) is about 7,926 miles.\n\nThe ratio of the circumference to the diameter of a circle (circumference/diameter) \nis written as the symbol pi. \nPi is approximately 3.141592.\n3.14159265\n3.1415926535\n\nTherefore, to determine the circumference from the diameter given above:\nequitorial diameter x 3.141592 = equitorial circumference\n| |\n7,926 x 3.141592 = 24,900\n| |\nThe earth has a circumference of approximately 24,900 miles.\n\nMore precisely the circumference of the earth\nat the equator is 24,902 mi / 40,076 km. \n\n------------------\n\nHow fast would you have to travel to see the sun set twice, \nor outrun the shadow of the setting sun?\n\nSince the sun "travels" once around the earth every 24 hours, \nwe can get the speed by dividing the circumference of the earth by 24:\n\nmiles divided by hours\n| |\n24,900 / 24 = 1,038 miles per hour\n\n....\n\nA RATIO of a to b can be expressed in three ways:\n1. a : b\n2. a / b\n3. a ÷ b
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The moon rotates on its own axis and orbitrs the planet Earth as Earth orbits the sun.\n\n\nFrom Wikipedia and verified though other sources:\nThe Moon is Earth's only natural satellite. It has no formal name other than "The Moon", although in English it is occasionally called Luna (Latin for moon), or Selene, to distinguish it from the generic "moon" (natural satellites of other planets are also called moons). Its symbol is a crescent. The terms lunar, selene/seleno-, and cynthion (from the Lunar deities Selene and Cynthia) refer to the Moon (aposelene, selenocentric, pericynthion, etc.).\n\nThe average distance from the Moon to the Earth is 384,403 kilometers (238,857 miles). The Moon's diameter is 3,476 kilometers (2,160 miles).\nThe Moon makes a complete orbit about the Earth approximately once every 28 days. Each hour the Moon moves relative to the stars by an amount roughly equal to its angular diameter, or by about 0.5°. The Moon differs from most satellites of other planets in that its orbit is close to the plane of the ecliptic and not in the Earth's equatorial plane.\n\nSeveral ways to consider a complete orbit are detailed in the table below, but the two most familiar are: the sidereal month being the time it takes to make a complete orbit with respect to the stars, about 27.3 days; and the synodic month being the time it takes to reach the same phase, about 29.5 days. These differ because in the meantime the Earth and Moon have both orbited some distance around the Sun.\n\nThe gravitational attraction that the Moon exerts on Earth is the cause of tides in the sea. The tidal flow period, but not the phase, is synchronized to the Moon's orbit around Earth. The tidal bulges on Earth, caused by the Moon's gravity, are carried ahead of the apparent position of the Moon by the Earth's rotation, in part because of the friction of the water as it slides over the ocean bottom and into or out of bays and estuaries. As a result, some of the Earth's rotational momentum is gradually being transferred to the Moon's orbital momentum, resulting in the Moon slowly receding from Earth at the rate of approximately 38 mm per year. At the same time the Earth's rotation is gradually slowing, the Earth's day thus lengthens by about 15 µs every year. A more detailed discussion follows in the section titled Earth & Moon.\n\nThe Moon is in synchronous rotation, meaning that it keeps the same face turned to the Earth at all times. This synchronous rotation is only true on average because the Moon's orbit has definite eccentricity. When the Moon is at its perigee, its rotation is slower than its orbital motion, and this allows us to see up to an extra eight degrees of longitude of its East (right) side. Conversely, when the Moon reaches its apogee, its rotation is faster than its orbital motion and reveals another eight degrees of longitude of its West (left) side. This is called longitudinal libration.\n\nBecause the lunar orbit is also inclined to the Earth's equator, the Moon seems to oscillate up and down (as a person's head does when nodding) as it moves in celestial latitude (declination). This is called latitudinal libration and reveals the Moon's polar zones over about seven degrees of latitude. Finally, because the Moon is only at about 60 Earth radii distance, an observer at the equator who observes the Moon throughout the night moves by an Earth diameter sideways. This is diurnal libration and reveals about one degree's worth of lunar longitude.\n\nEarth and Moon orbit about their barycenter, or common center of mass, which lies about 4700 km from Earth's center (about 3/4 of the way to the surface). Since the barycenter is located below the Earth's surface, Earth's motion is more commonly described as a "wobble". When viewed from Earth's North pole, Earth and Moon rotate counter-clockwise about their axes; the Moon orbits Ea
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I'm not sure about the distance to the moon, but I can explain the rest...\n\nLots of questions here... \n\nFirst, they found out about the curvature of the earth mainly by observing the earth's shadow on the moon during a lunar eclipse. You can easily see the Earth's shadow as curved and not straight.\n\nThe experiment with the sticks, performed by Eratosthenes, was to determine the circumference of the earth, and thus, how big it is.\n\nYou're absolutely right with the argument that the shade produced by a stick on a flat surface would be different than that on a curved surface.\n\nEratosthenes went with the [correct] assumption that the sun was so far away, that its light rays striking the earth would be parallel to each other.\n\nIn truth, this only occurs for an object that is infinitely far away, but the sun is SO far away, that this difference, from two different places on Earth, is negligable.\n\nSo if you have a flat surface, then no matter where you are on the surface, the shadow cast by a stick should be the same. If its noon, and the light rights are parallel, and the Earth is flat, then there should be no shadow no matter where you are on the surface.\n\nNow, Eratosthenes saw that at noon, in two different cities, that in one city, there was no shadow cast by the stick, meaning the sun was directly overhead, and at the same time in the other city, there was a small shadow, and measured the angle the stick made with the shadow. \n\nHe noticed the angle was about 7 degrees, which means its 1/50th of a full circle (360 degrees). Therefore, the two cities were 1/50th the way around the globe. Knowing how far the cities were, he multiplied their distance by 50 and got the distance around the globe. c = 2*pi*r, so he could then calculate the radius of the earth as well!\n\nThat's pretty much it, hoped you understood it. Its really amazing how they could get the size of the earth simply by using two old sticks and a little thought! :)
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It doesn't GET any bigger than it is, it just LOOKS bigger because it really IS nearer\n\nBecause its distance from the earth varies as the orbit is not a circle, as you asssume, but an ellipse (oval).\n\nThe furthest distance from the earth that the moon reaches in any orbit (lunar month) is called the APOGEE and the nearest distance it approaches in that orbit is the PERIGEE.\n\nIn the table below the distances are in kilometres, measured from the centre of the earth to the centre of the moon.\n\nJust gone:\n\nMar 13  APOGEE 406272 km \nMar 28  PERIGEE 359169 km\n\nComing up soon:\n    \nApr  9 APOGEE 405549 km    \nApr 25 PERIGEE 363735 km  \n\nThe earth's orbit round the Sun is an ellipse too, and the nearest distance in any one orbit (year) is called PERIHELION and the furthest distance in that orbit is called APHELION.\n\nHelios is the Greek word for the sun and Peri- and Ap- are prefixes meaning near to and far from. The sun looks correspondingly smaller at aphelion and larger at perihelion.  \n\nSometimes eclipses of the sun are not quite total if the sun is bigger than usual (near or at perihelion) and the moon smaller than usual (near or at apogee).\n\nThere is a more pronounced variation in the distance between Earth and Mars than either the variation in Sun-Earth or Earth-Moon distances. Mars looks a lot brighter and a lot dimmer as a consequence, at these times.\n\nTo visualise why, think of a clock face. The sun is in the middle of the dial. The earth is on the tip of the hour hand and Mars is on the tip of the minute hand. When the time on the clock face is midnight, five past one, ten past two etc earth and Mars are at their closest. When the time on the clock face is 12.33, 1.37, 2.43 etc Earth and Mars are at their furtherst apart, Mars being the radius of an earth orbit plus the radius of a Mars orbit away, beyond the Sun.\n\n(This too-simple model assumes circles not ellipses and assumes that Mars years are twelve Earth years, where in reality Mars years are only about twice an Earth year. But it gives you a general idea.)
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The average distance from the Moon to the Earth is 384,403 kilometers (238,857 miles). The Moon's diameter is 3,476 kilometers (2,160 miles).
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The Moon's orbit around the Earth is elliptical, with a substantial eccentricity (as major Solar System bodies go) of 5.49%. In addition, the tidal effect of the Sun's gravitational field increases the eccentricity when the orbit's major axis is aligned with the Sun-Earth vector or, in other words, the Moon is full or new.\n\nAt Perigee (its closest Point to earth the Distance is  359861 km from earth measured from equator to equator.\n\nAt Apogee (its farthest point from eath the Distance is 405948 km from eath measured from equator to equator.\n\nAs it revolves around the earth in this EGG shaped orbit it cycles between getting further and closer from earth.\n\nTake a Boiled egg and cut it in half. Measure how THICK the white is from the yoke at any point on the FLAT cut surface of the egg. The moon would travel around the outside of the yoke. (the yoke is the earth.\n\nSee the below link for a great explanation and good photos and graphics.
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It is presumed that we perceive the sun/moon larger near the horizon because its in close proximity to buildings and other frames of reference, and our eyes compare the size of the moon to the buildings and other horizon features. \n\nUp in the sky, there is no frame of reference, and without it, the moon appears smaller.
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The moon is closest at about 1/4 million miles, the sun is next, about 93 million miles, and the nearest star is Proxima Centauri, about 4 light years (3,800,000,000,000,000,000 miles)
90872
the moon doesnt circle the sun the moon circles the earth the earth circles the sun
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The average distance between Earth and Moon is approximately 30 times Earth's diameter.
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a. No, Hubble’s law can be used to determine the distance of Centauri and other stars relatively close to the Sun because it can’t be used to find the distances of stars in our own Galaxy for they are gravitationally compelled to our Galaxy and the increase of the intervening space is surmounted. b. No, Hubble’s law can be used to determine the distance of the center of our Galaxy because it can’t be used to find the distances of stars in our own Galaxy for they are gravitationally compelled to our Galaxy and the increase of the intervening space is surmounted. c. No, Hubble’s law can be used to determine the distance of the Large Magellanic Cloud, which is a satellite of our Galaxy because it can’t be used to find the distances of stars in our own Galaxy for they are gravitationally compelled to our Galaxy and the increase of the intervening space is surmounted. d. Yes, Hubble’s law can be used to determine the distance of a cluster of galaxies very far from the Local Group because it can’t be used to find the distances of stars of our Local Group for they are gravitationally compelled to our Galaxy and the increase of the intervening space is surmounted.
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If you write the number sequence 0,3, 6, 12, 24, 48, 96, and add 4 to each number (4, 7, 10, etc) then divide by ten, you get the distance of each planet from the Sun, measured in astronomical units (1 a.u.=93 million miles=150 million kilometers).  This works out as Mercury 0.4, Venus 0.7, Earth 1.0, Mars 1.6, --- 2.8, Jupiter 5.2, and Saturn 10.0  This works out pretty accurately, but there was nothing at 2.8. Herschel discovered Uranus in 1781 at 19.6, right where another planet was supposed to go according to the Titius rule.   When Ceres was discovered in 1801, it was at 2.72, filling the gap.  Neptune, however is not near 38.8, but at 30.  Astronomers now believe the "law" is either a coincidence, or the result of billions of years of gravitational interactions.
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Distance to the Moon\n\n  \n  \n  \n  \n     \n An Astronomy Tid-Bit about the mean and extreme distances to the Moon\n\n  \n  \n  \n  \n     \n   Note:  Distance is from center to center of orbiting bodies.\n             Kilometers divided by 1.6093 = miles.       \n\n      Many sources, such as beginning astronomy textbooks, yearbooks, and atlases, give the distance to the moon as 384,400 kilometers (km), and  0.055 as the flattening or eccentricity of the moon's elliptical orbit around the Earth.\n\n      The moon travels around Earth in an elliptical orbit, with the Earth at one of the two focuses (foci) of the ellipse.  As a result the distance to the moon varies by quite large amounts.  Its close (or perigee) distance is 384,400 x (1- 0.055) = 363,258 km.  Its far (or apogee) distance is 384,400 x (1+0.055) = 405,542 km.  BUT these values turn out to be the mean or average values.  See the table below for actual distances.\n\n      The actual (computed) distances over 10 centuries, from  1500 to 2500, have been calculated by the Belgian astronomer, Jean Meeus, to be as small as 356,371 km or as large as 406,720 km./1 These values differ from the MEAN values by 6,887 km and 1,178 km respectively\n\n      An excellent and easy-to-use source for the moon's position and distance is "Multiyear Interactive Computer Almanac" produced by the US Naval Observatory, Wash. DC and published by Willman-Bell, Inc., PO box 35025, Richmond, VA  232235.  The program called "MICA15" is on one CDRom for both IBM and MAC systems.  Included with the disk is an information and instruction book.\n\n      I used MICA15 to scan moon distances for the one  year, 2000, shown in TABLE 1.  The same source was used for the ten-year period, 1995 to 2005.  For this ten years,  the smallest distance (356,613.970 km) between Earth and Moon for this period occurred on November 4, 1998.  The largest occurred on March 14, 2002 when the moon was 406,706.975 km away.