What is the evidence that early astronomers used to show ...



1. The Earth orbits the Sun.FROM THE MARCH 2017 ISSUEWhat are the accepted proofs that Earth revolves around the Sun? When did this realization take place?Published: Monday, January 30, 2017We had no direct view of Earth until the dawn of the Space Age. Finding physical evidence that our planet revolves around the Sun took some clever thinking to prove that this heliocentric model of our solar system represents reality.The idea is ancient. Around 230 b.c., the Greek philosopher Aristarchus suggested that this was the case. He was an outstanding observer and based this idea on careful observations. Still, without direct proof that Earth moves, Aristotle’s Earth-centered universe remained the dominant model for centuries.In 1610, Galileo turned his new telescope toward Venus. To his amazement, he saw the planet pass through phases just like the Moon. Galileo correctly surmised that this could happen only if Venus had an orbit closer to the Sun than Earth’s orbit.With improved telescopes, astronomers started looking for another proof of Earth’s motion around the Sun, stellar parallax. Earth’s orbit is huge — some 186 million miles (300,000 kilometers) in diameter. If an astronomer measures the position of a nearby star, and then measures it again six months later, the star’s apparent position against the background of more distant stars should shift a tiny amount.Observing this would prove that Earth in fact is not stationary. It wasn’t until 1838 that an astronomer finally detected this shift. That year, German astronomer Friedrich Wilhelm Bessel successfully measured the parallax of the star 61 Cygni.And there’s yet another proof. Imagine standing still with rain coming straight down. To stay dry, you just hold your umbrella directly over your head. As you begin to walk, however, you need to tilt the umbrella “into” the rain, even though the rain is coming straight down. The faster you walk, the greater the tilt needs to be.As Earth orbits the Sun, we can detect a “tilt” of incoming starlight. English astronomer James Bradley discovered this phenomenon in 1725 by accident — while he was searching for stellar parallax! This aberration of starlight, as it is called, is a result of light having a finite speed and Earth’s motion around the Sun.Raymond Shubinski?? Contributing Editor?? . It takes the Earth about 365.25 days to complete its orbit around the Sun in a counterclockwise direction.(Every four years we have a leap year on February 29 to make up for the fact that a year is actually 365 and ? days long.)People have known for a very long time that the length of a year was 365 days. Careful observation of the sun e.g. when it rises, when it reaches the highest point in the sky, can tell you that the earth takes about 365 days to get back the the same point. Ancient stone observatories such as Stonehenge, built over 5000 years ago, seem to be designed to pinpoint the summer solstice (June 21). People knew it was 365 days from one solstice to the next.?The question of WHY the year is 365 days long was controversial for many centuries. The idea that the earth orbits the sun was held by some Greek philosophers, most notably Pythagoras, but it was not until the 17th century and the calculations of Copernicus and the observations and writings of Galileo that people started to accept that the earth orbited the sun and not vice versa. The idea was considered heresy by the Catholic Church.?It takes 365.25 days to complete one revolution. And that's why we have leap year .Example?: suppose we place a stick on the group and observe it's shadow then we could easily see the shadow is different everyday and it takes 365 days for that stick to make the initial shadow on that first day.?. The earth takes about 24 hours to completely rotate on its axis.The idea that the Earth is rotating was not given serious thought until the 16th century when Polish astronomer Nicolaus Copernicus proposed that the Earth goes around the Sun. Once Copernicus’ idea was accepted, a rotating Earth was the only way to explain why there is day and night. However, scientists like to gather as much empirical support for an idea as possible, so physicists came up with other ways to show that the Earth is rotating.A century after Copernicus, English physicist Isaac Newton predicted that, if the Earth is rotating, it should be slightly squashed at its poles and slightly bulged at its equator. Evidence for this was found in the 18th century.Another simple test for Earth’s rotation came from what’s called a Foucault’s pendulum, named after 19th century French physicist, Leon Foucault. A pendulum consists of a string or stick with a weight suspended at the end of it that is allowed to swing freely. A grandfather clock is an example of an everyday object that uses a pendulum. Foucault’s original pendulum consisted of a metal sphere at the end of a long wire suspended from the top of the Pantheon in Paris. If the Earth is rotating, then instead of swinging perfectly back and forth, the pendulum’s plane of oscillation should rotate a little bit with the Earth’s rotation. That’s exactly what Foucault’s pendulum demonstrates. is the evidence that early astronomers used to show that the Earth is turning on its axis?By?Dr. Sarah Salviander UT Austin 20 Nov 20154. The earth’s orbit is very slightly elliptical and is closest to the sun on about approximately January 3 and is furthest from the sun around July 4. It is about 3 percent closer in January than it is in July.Why Earth is Closest to Sun in Dead of WinterBy Mary Lou Whitehorne, Special to | January 2, 2007 It's winter in the Northern Hemisphere and we're at our closest point to the Sun. ……But our non-circular orbit does have an observable effect. It produces, in concert with our tilted axis, the analemma.If you plot the noontime position of the Sun in the sky over a one-year period, it produces a figure-eight shape on the sky (Figure A). This is the analemma. You may have seen it drawn on a globe of Earth. The shape results from the combination of two things: the 23.5° tilt of Earth on its spin axis, and the elliptical shape of Earth's orbit around the Sun.The highest point on the analemma is the Sun's noon position on the summer solstice. The lowest point marks the winter solstice. The difference in the Sun's noontime height in the sky is caused by Earth's tilted axis. What about the left-to-right variation in the analemma's curve?That's where our elliptical orbit comes in! Look at Figure A again. Notice the vertical line running up from the south point on the horizon? That's the meridian. The meridian runs straight up and over the sky, from due north to due south.If Earth's orbit was a perfect circle, the Sun would cross the meridian at noon every day (ignoring daylight savings time). But our orbit is slightly oval-shaped. In July, we are at our furthest point from the Sun, and Earth moves slower than average along its path. In January, we are closer to the Sun, and Earth speeds up a bit in its orbital progress. The result of this change in speed means the Sun crosses the meridian a little early, or a little late, depending on where Earth is in its orbit. For all points along the curve to the left of the meridian, the Sun is "slow." It crosses the meridian after 12:00 p.m. For all points along the curve to the right of the meridian, the sun is "fast," crossing the meridian slightly before noon.. In the Northern Hemisphere the Winter Solstice which is the shortest day of the year is around December 21. (This is the Summer Solstice for the Southern Hemisphere.) At the North Pole there is a period of time in the late fall and early winter when the sun never rises and it is dark all day and all night. many ancient civilizations that struggled to subsist through harsh winter months, the?winter solstice?marked a time of spiritual rejoice and celebration. Modern heating technology and the globalization of food markets make the seasonal transition remarkably easier for modern humans to survive, but people still do celebrate the day with festivities and rituals, including a tradition of reading poetry and eating pomegranates in Iran, and the Guatemalan ritual known as polo voladore — or "flying pole dance" — in which three men climb to the top of a 50-foot-tall (15 meters) pole and perform a risky dance to flutes and drums.?6. In the Northern Hemisphere the Summer Solstice which is the longest day of the year is around June 21. (In the Southern Hemisphere this is the Winter Solstice.) At the North Pole there is a time in summer when the sun never sets and it is light all day and night. 7. In the Northern Hemisphere the Fall (Autumnal) Equinox in which the day and night are equal is around September 23.People throughout history have marked the equinox and the solstice. And no one has done it in more spectacular fashion than the Maya, who constructed the El Castillo step pyramid at Chichen Itza in Mexico so that a snake made of light would appear to slither down the pyramid’s steps at the autumnal and vernal equinoxes.“Standing at the corner of the building with the sunset to my right, looking on the left, you see the big stairway going up the side of the building, and you’ll see the light of the un-shadowed portion looks like a snake on the stairway,” says anthropologist?James Fox, who has worked at Chichen Itza.. The Spring (Vernal) Equinox in which day and night are equal is around March 20.In many cultures, the March Equinox marks a time of transition and new beginnings. It's the Vernal (Spring) Equinox in the Northern Hemisphere, while in the Southern Hemisphere it's the Autumnal (Fall) Equinox.Easter comes after the March Equinox?Shannon LongWhen is the March Equinox?Here are some ways people around the world celebrate and observe the March Equinox:Some Bring Out the Easter EggsIn addition to being the Spring (Vernal) Equinox in the North and the Fall (Autumnal) Equinox in the South, the date of the March Equinox plays a huge role in calculating the dates for when to celebrate Jewish Passover and Christian Easter.How is Easter and other Holidays celebrated?In many Christian cultures, Easter eggs are synonymous with Easter. Also known as Paschal eggs, these are usually decorated chicken eggs that symbolize fertility and rebirth. Many Easter related events feature the Easter egg as the central theme. Traditional games like egg hunts, where children search for colorful Easter eggs; egg rolling, where eggs are rolled down a hill; and egg dancing, where eggs are laid on the floor and people dance while trying not to damage them, are held all around the world.10 Things about the March Equinox...And Try to Balance ThemAn ancient Chinese tradition calls for balancing eggs, a symbol of fertility, on the day of the March Equinox for good luck and prosperity.This ancient custom has given rise to a modern myth. Every year, during the March Equinox people claim that it is the only day of the year when an egg can be perfectly balanced on its end. A version of the claim suggests that eggs can only be balanced on their end at the exact time of the Equinox. The truth is that there is nothing magical about the Equinox or the time it occurs - you can balance an egg perfectly on its end on any other day as well.March Equinox in your local timeOthers Ring in Their New YearThe Iranian New Year (Nowruz, No-Ruz, No-Rooz or No Ruz) occurs during the time of the March Equinox, in accordance with the Persian astronomical calendar. It has been celebrated for over 3000 years and is rooted in the traditions of Zoroastrianism. No-Ruz celebrations last for about 12 days. Preparations start well in advance and include buying new clothes for family members and thoroughly cleaning homes. Wheat or lentil representing new growth is grown in a flat dish a few days before the New Year and is called Sabzeh (green shoots).Other holidays in IranIn Japan, People Remember their AncestorsHigan (Higan-e or Ohigan), is a week of Buddhist services in Japan during the March and September Equinox. Both equinoxes have been national holidays since the Meiji period (1868-1912)."Higan" means the “other shore” and refers to dead spirits who reach Nirvana after crossing the river of existence. It celebrates the spiritual move from the world of suffering to the world of enlightenment.. The earth’s axis is tilted 23.5 degrees with the North Pole directing towards Polaris (the North star). The very short bright trail?near the NCP?was made by the?star Polaris, commonly known asthe North Star.The axial tilt of the Earth has been known for a surprisingly long time. The first reasonably accurate measurements were made in China and India. The first (that we know of) was made in 1100 B.C. (over 3000 years ago!) by Chou Li. The next set of measurements came from greek geographers about 750 years later.All you really need to estimate the tilt of Earth's axis is a carefully positioned pole. Ancient calculations of the axial tilt were made by measuring the length of a shadow cast by a gnomon (a vertical pole) during summer and winter solstice (the longest and shortest days of the year). If the Earth's axis weren't tilted, a rod at the Equator would cast no shadow at noon. Because the axis is tilted, such a rod casts a north-south shadow that varies throughout the year. However, a rod placed on the Tropic of Cancer does not cast a shadow at noon during the summer solstice, and a rod placed on the Tropic of Capricorn does not cast a shadow at noon during the winter solstice. Ancient geographers were very clever and curious people. With vertical rods and some ingenuity, they made pretty accurate measurements of the tilt of Earth's axis.? ................
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