The transit of venus: viewing tips from an astronomer - China Stovetop Coffee Maker

The transitof Venus, as it is called, is a very rare event in our solar systemdue to the relative alignments of the orbits of Earth and Venusaround the Sun. Venus orbit is inclined at an angle just under3.5 with respect to Earth s. This may seem small, but onastronomical scales, this means that Venus will only pass betweenthe Earth and the Sun directly along our line of sight twice every120 years or so. This occurred in 2004, but unfortunately was notvisible from much of the U.S.

and the next pair of transits won ttake place until 2117. The importance of this event is now mostly historical, but at onetime it was essential to understanding the scale of our SolarSystem. While Kepler s laws of planetary motion and IssacNewton s law of universal gravitation allowed for the calculationof the relative distances of the planets from the Sun, but nothingwas known in absolute terms. In 1716, Edmund Halley was the firstto propose that measurements of the transit of Venus would allowfor the Sun-Earth distance to be estimated.

However, it wasn tuntil the 1761 and 1769 transits that astronomers were able toobtain useful measurements that led to the first calculations ofthe true distance between the Earth and the Sun. (The above graphic originally appeared in The New York Times ). This was accomplished through the principles of parallax. Asillustrated in the figure above, two observers on different pointsof the Earth were needed to observe the transit independently.

Eachwould record the time Venus first crossed into the disk of the Sunand the time it left it. Using the known separation distance of theobservers on Earth, the distance to the Sun could then becalculated. Once the Earth-Sun distance was calculated, the distances to allthe other planets known at the time could be derived. As successivetransits have occurred, more precise measurements were made and theEarth-Sun distance was refined.

It was the last transit in 1882that yielded our current estimate of approximately 93 million milesand defined our standard distance of the Solar System: theastronomical unit (AU), i.e. 1 AU = 93 million miles. As you can imagine, coordinating observers around the planet is alot easier now then it was in the 1700 s and 1800 s. One poorFrench astronomer was sent to the southeast coast of India toobserve the 1761 transit, but his destination was deemed toodangerous en route due to the Seven Year s war between France andBritain. He tried desperately to reach a safe landing point, butwas still at sea when the transit occurred and was unable to takeany useful data on the rocking deck of the ship.

Reasoning that thenext transit was only eight years away, he decide to wait it out inthe Indian Ocean, passing the time mapping part of Madagascar. When1769 arrived, he set sail for the Philippines but was once againderailed by international conflict, this time with the Spanish.Retreating to his original target in India, he arrived in plenty oftime to view the transit only to be thwarted at the last minute byovercast skies. If that weren t enough, when he finally gatheredthe strength of mind to return home, his tumultuous journey homeculminated in the unpleasant discoveries that he had been declarelegally dead, his wife remarried, and his family had divided up hisestate. There have now been six transits of Venus observed by humans sincethe invention of the telescope in 1609.

Here are a few tips for howyou can be part of the seventh without having to set sail for aforeign land: First, check to make sure you are located in a place where the transit will be visible . Decide which method of observing the transit works best for you. If you are located somewhere outside of the viewing area or ifmother nature decides not to cooperate, never fear, NASA will be webcasting the transit from Mauna Kea in Hawaii. My method of choice (absent a telescope with a solar filter) is a pinhole projector as it requires little more than some cardboard, some aluminumfoil, and a direct sightline to the Sun. It also enables more thanone person to watch the transit at a time.

The only tradeoff isthat the larger you make the projected image of the Sun (i.e., thelarger the distance between the two pieces of cardboard), thefainter it gets. You can get around this by using a very long box to enclose the pinhole projector on three sides, which willpreserve some of the brightness. Regardless of your plans for the transit, please remember that youshould never look directly at the Sun without proper protection.Viewing the Sun through clouds, sunglasses, unfiltered telescopes,binoculars or cameras can result in instant and permanent damage. That being said, happy transiting! Summer Ash is Director of Outreach for the Department of Astronomyat Columbia University and an instructor for Frontiers ofScience in the Core Curriculum. Her doctoral research was on theevolution of radio galaxies and active galactic nuclei.

Shevalues the power of the scientific method, the history ofscience and the necessity of skeptical inquiry. As aself-professed space cadet, Summer grew up dragging friendsand family out at all hours of the day or night to look up atthe sky. In her previous life she was a rocket scientist, butnow enjoys getting paid to spread her love of space with anyone whowill listen. She attempts to blog at Newtonianism for theLadies, tweets as @Summer_Ash, and is the in-houseAstrophysicist for The Rachel Maddow Show.

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