Parallax refers to the difference in an object’s relative location as seen from different perspectives.
Mathematically speaking, you can sum up the relationship between any two observation points (or distant object) in what is known as a parallax angle.
So long as some of the information is known – such as an angle between the lines of sight and the distance between observations – trigonometry can be used to deduce how far away the object is.
This intuitively happens on a personal level. Each eye’sees” objects according to its own line of sight. Differences in objects’ positions are interpreted by the brain as perpendicular distance or depth.
This is why objects appear immediately to us as three-dimensional.
Parallax angles are able to describe longer distances on increasingly large scales, including between Earth and other astronomical bodies like the Sun or nearby stars.
How does parallax work for astronomers?
In order to measure the enormous distances between objects in the inner Solar System, like the Sun and Earth, early astronomers had the task of increasing the gap between observer positions so that it could be measured on a scale of whole continents. This was done by jumping from one side to the other.
Centuries ago astronomers travelled across oceans to view the inner planets of the Sun. Transits are such planetary crossings. are rare eventsThis relies on an exact alignment between Earth, the planet being observed and the Sun.
Predicted transit of VenusIn 1769, there were observers from all over the globe, from North America to Russia to Europe. Tahiti, further southCollect data about the relative distances and timing The apparent pathsAs it traveled from one side to the Sun’s disk, the tiny silhouette of the planet captured its attention.
Two years later a French astronomer named Jérôme Lalande applied those measurements, along with some from an earlier transit, to come up with an estimate of 153 million kilometres (95 million miles) between Earth and the Sun; just a touch over the currently accepted figure of around 149,600,000 kilometres.
Distances between observations of objects outside our Solar System must be greater than the distance between two planets.
Earth’s orbit is able to provide such a gap. It covers more than 300 million kilometers (186 million miles).
Also, spacecraft can provide another point from which to measure distance. NASA’s New Horizon probeThe spacecraft, which made a flyby at Pluto, is still exploring the outer Solar System It was exactly what he did.
The European Space Agency’s Gaia Space ObservatoryNow, he is focusing on the monumental task of recording the positions around a billion astronomical items.
Gaia orbits the Sun from a distance of approximately 1.5 million kilometers from Earth. It will notice tiny differences in the apparent positions these objects at different points on its annual journey.
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Applying parallax angles to Gaia’s measurements will produce rough estimates on objects as far away as 30,000 light-years away – a distance between Earth and the middle of the Milky Way. The measurements of distant objects could be even more precise. Within 0.001 PercentActual distance
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