here’s a fabulous world map / data by Fred Espenak of NASA. (His website is one I use regularly for a lot of astronomical data, especially Eclipses…and now for this. If you are quoting this or him, please due acknowledgement to Fred Espenak. Thank you)
Transit of Venus- what is it and how does it happen:
Venus transit (and eclipses) are all similar.. In Solar Eclipses, the moon comes between us on earth and blocks the Sun for a bit. In transit of venus, the planet Venus comes and blocks the Sun out. except because the Venus is further away from us, but closer to the Sun, it doesn’t `seem’ to cover the whole of the Sun.. It just appears as a small spot passing across (in front) of the Sun.
Because of orbits, geometry (relationship between shapes, distances, angles) and speeds of planetary motion, the transit of Venus `happens’ (for us!) twice every century (once, then 8 years later, then next century). After 6th June’12, next transit of venus will be in the year 2117 (unless you have the secrets of long life, you won;t live to see it again). The last time this event occurred (as it happens on pairs) was on June 8, 2004.
Time variations Why?
Stellar events (like planets moving) take time. The Transit of venus is – simply put- us from Earth viewing the Sun and Venus. Planets are moving around the Sun in different orbits (circular or elliptical paths). Because of the geometry of shapes and distances involved (ie planets are spheres, and distances between Sun, venus & earth are vast!), what we view from earth changes. Specifically, where on Earth you are located makes a big difference to the exact image you will see.. It’s a bit like watching the Football in a field being kicked about – what you see depends on where about in the auditorium / seats you are at. It’s one event (the ball moving on the ground.. but thousands of people watch it from different parts of the stadium..).
Visibility of transit of venus
Anyway, when the transit of venus starts, it will be different times.. for different parts of the world (time zones). Here’s the thing- for some people, it will actually be middle of the night! That means they can’;t see the Sun (!), and if ya can;t see the Sun, you can’t see Venus going in front of the Sun. In the map attached, you can see the shaded parts of the world `No transit visible’. If you are in one of those counties, or parts of those countries, alas, you are having night time.. so you won;t see it. (parts of South America, parts of Africa). For everyone else, the transit of venus is visible.. at least the beginning, middle, or end of the transit.
For the people in Australia, for example, the time happens to be Sunrise..when transit of venus starts…Lucky them.- they get to see the whole event…from beginning to end. For those of us in UK, as Sunrise occurs (our time), the transit is almost over, but we still get to see the end of it..
Start & End times (Universal Time equals GMT for all intends and purposes)
In the NASA site, Fred Espenak gives times for this transit as below. I have added simple *explanations of what we `see’
Phase +Time *Explanation (by Mani Navasothy) Contact I 22:09:38 (outer edge of Venus first `touches' the Sun's edge). Contact II 22:27:34 (whole of Venus first fully `inside the Sun disc). Greatest 01:29:36 (Venus in the mid-part of transit). Contact III 04:31:39 (edge of Venus starts to come `out of the Sun' disc) Contact IV 04:49:35 (trailing end of Venus fully `leaves' the Sun disc).
+Don’t forget your local `summer time adjustments’. Here in UK, for example, the `Greatest Transit’ at 01:29 hrs UT/GMT is seen at local British Summer time of 02:29 hrs .
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2 thoughts on “Astronomical Data & visibility Map for Transit of Venus: What, where and how long”
Terrific post, Mani! Thank you for explaining it so well! It’s a shame we UK folks are going to largely miss it. I can’t see me getting up at 4 AM to catch a glimpse of it either!