Venus is the second planet from the Sun in our Solar system, more information regarding the planet can be found in one of my previous entries here.
A transit is the passage of an inferior planet across the face of the sun (or of a moon or its shadow across the face of a planet). So, a transit is similar to a solar eclipse by the moon, and the Venusian transit lasts for a couple of hours; 50 minutes or up to 6 hours depending on your location of course. These transits are also called the black drop effect because of their appearance when passing in front of the Sun.
Transits of Venus only occur a few times every century because of the Earth-Venus geometry. These transits have been used by ancient astronomers to get a sense of scale in the Solar System. It's important to mention that these transits don't occur once every year, like you'd imagine, simply because the orbit of Venus is shifted 3.4 degrees relatively to the Earth's.
|the inclination between the two orbital planes is 3.4°|
Venusian transits are among the rarest of predictable astronomical phenomena. They occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years. The first transit of the twenty-first century pair took place in 2004, the second one will occur on june 5 or 6 2012, depending on your timezone. For a timeline of all the transits of Venus, click here (and then scroll down). The next one will take place in december of 2117, unless you plan to live for an extra 105 years, this is one more reason for you not to miss this!
This event will be visible from various locations around the Blue Planet, some better than others.
To get a better sense of when to look observe the sun, NASA's Goddard Space Flight Center made a list of 121 international cities with corresponding transit contacts, make sure you see it here, you can find any city easily. If you're unlucky enough to be in Portugal, Spain, Brazil, Argentina, or Uruguay during this time, or if you don't want to wake up before sunrise, the Mauna Kea Observatory from the The University of Hawaii Institute for Astronomy will broadcasting a live webcast of the transit, in collaboration with NASA scientists. Since it's summer, I advise you to use an astronomical excuse for a vacation. Sky At Night Magazine recently wrote an entertaining article listing holiday options in well-calculated locations for perfect black-drop observation from places like Hawaii, Sydney and even a Tahitian cruise ship, read it here!
There are four named "contacts" during a transit, moments when the circumference of Venus touches the circumference of the Sun at a single point:
- First contact (external ingress): Venus is entirely outside the disk of the Sun, moving inward
- Second contact (internal ingress): Venus is entirely inside the disk of the Sun, moving further inward
- Third contact (internal egress): Venus is entirely inside the disk of the Sun, moving outward
- Fourth contact (external egress): Venus is entirely outside the disk of the Sun, moving outward
A fifth named point is that of greatest transit, when Venus is at the middle of its path across the solar disk and which marks the halfway point in the timing of the transit.
This video gives you an idea of what you're going to see, it's merely an animated sequence of pictures taken by a terrestrial telescope.
For tips on how to better observe the transit, consult an eye-safety article here. Looking directly at the sun can be harmful, and may cause permanent damage. Beware, wearing sunglasses is in no way sufficient. Some helpful tips for safe viewing are:
- Solar viewing devices such as solar filters for you telescope
- Build a Sun Funnel for your telescope, here's an illustrated guide
- Eclipse Shades or Solar Shades that appear similar to sunglasses, but they have a special filter that permits safe viewing if the filter is in new condition
- Pinhole projectors that are usually used to observe solar eclipses
- You can project a magnified view of the sun, details on how can be found here
- Watch a live online webcast here.
For all you Apple and Android phone users, download the free app! (yes, there is an app for everything). Don't forget to set reminders! And don't forget to share good photos of Venus' visit.
This is an example of the transit's main events when viewed from Beirut, generate one of these by typing in you location using this website!
|Transit Of Venus From Beirut|
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