APOD: Venus Transit 2012 (2012 Jun 07)

[APOD Robot]

Venus Transit 2012

Explanation: Occurring in pairs separated by over a hundred years, there have now been only eight transits of Venus since the invention of the telescope in 1608. The next will be in December of 2117. But many modern telescopes and cameras were trained on this week's Venus transit, capturing the planet in rare silhouette against the Sun. In this sharp telescopic view from Georgia, USA, a narrowband H-alpha filter was used to show the round planetary disk against a mottled solar surface with dark filaments, sunspots, and prominences. The transit itself lasted for 6 hours and 40 minutes. Historically, astronomers used timings of the transit from different locations to triangulate the distance to Venus, while modern astronomers actively search for planets that transit distant suns.

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[Flase]

There looks like some sort of giant parasitic worm writhing on the surface...

[Moonlady]

There looks like some sort of giant parasitic worm writhing on the surface...

And some of those worms beamed thousands of years ago towards earth, flew through the atmosphere. They were hit and washed by
raindrops, the worms grew to serpents, each of them in a different color. They leaned to each other and hit the ground in Australia,
their bodies made a bow. Sun and raindrops made them shine. People were excited and welcomed these serpents.
The serpents protected the people and their waterholes. The serpents resided in the waterholes.
These serpents saw that people loved them and they showed their gratitude by appearing in colors each time sun and rain united on earth.


And they happily... actually that was a little different... the Rainbow Serpent is an Australian Native Mythe.

[Flase]

Yes they have serpents in Australia. Not so in NZ. They also have bigger uglier spiders that bite you on the bottom when you're sitting on the dunny...

[elrenno]

I'm confused about something. Why is it we only see a transit every hundred years or so? With Venus' orbital rate and Earth's orbital rate, I would think we would see a transit about every 8 months. Are our orbital planes different or what?

[Chris Peterson]

I'm confused about something. Why is it we only see a transit every hundred years or so? With Venus' orbital rate and Earth's orbital rate, I would think we would see a transit about every 8 months. Are our orbital planes different or what?

Every planet orbits on a different plane. Earth's and Venus's are several degrees apart.

[Byork]

Venus is tidally bound to the Earth - a condition which was first observed with radar transmission from terrestrial radio telescopes. As a result, a hemisphere of Venus faces the Earth every time the two planets come close together over a number of years. Initially, Venus probably revolved about its axis in the same direction as the other terrestrial planets. However, over eons of gravitational attraction to the Earth, Venus developed a retrograde rotation about the axis. Development of the retrograde axial rotation would also explain the absence of a Venusian magnetic field comparable to the Earth.

[Chris Peterson]

Venus is tidally bound to the Earth - a condition which was first observed with radar transmission from terrestrial radio telescopes. As a result, a hemisphere of Venus faces the Earth every time the two planets come close together over a number of years.

Venus is not tidally locked to the Earth. It has very close to a 5:1 resonance between its day and the period over which it comes closest to the Earth (584 days), so we see almost, but not quite, the same hemisphere each inferior conjunction. It is not known if the observed near-resonance is a coincidence or is driven by some sort of gravitational locking mechanism. I think the general view is that there is no Earth-Venus tidal resonance.

Initially, Venus probably revolved about its axis in the same direction as the other terrestrial planets. However, over eons of gravitational attraction to the Earth, Venus developed a retrograde rotation about the axis.

That is certainly not true- the forces are too small and the time too short. There are different ideas about how Venus developed its slow, retrograde rotation. The most likely involve some sort of solar tidal locking, or collisions early in the history of the Solar System.

Development of the retrograde axial rotation would also explain the absence of a Venusian magnetic field comparable to the Earth.

No, it doesn't. Venus is rotating fast enough that it would produce a large magnetic field if its core dynamics were the same as Earth's. The lack of a magnetic field is presumed to be the result of a lack of internal convection, or the lack of any solid core, or the lack of any liquid core.

[scr33d]

I'm confused about something. Why is it we only see a transit every hundred years or so? With Venus' orbital rate and Earth's orbital rate, I would think we would see a transit about every 8 months. Are our orbital planes different or what?

Every planet orbits on a different plane. Earth's and Venus's are several degrees apart.

For graphs:
http://www.skyandtelescope.com/observin ... 56885.html

[PhilT Sweden]

Hi - what is the white ring round Venus ? Is it the atmosphere we are seeing or some light bending/lensing around a massive object ?

[Bix Dugan]

Maybe this is a dumb question... If this event is so infrequent, How did the first observer even know WHEN to point the telescope at the sun?

[Chris Peterson]

Maybe this is a dumb question... If this event is so infrequent, How did the first observer even know WHEN to point the telescope at the sun?

Rare doesn't mean unpredictable. As soon as we had developed a mathematical system for describing orbital dynamics, and could apply it to the bodies in the Solar System, predicting such events became straightforward. Indeed, it was Kepler himself who first predicted a transit of Venus. That transit, in 1631, was not observed (because it was not visible from Europe), but all seven since then have been accurately predicted and observed.

[Steve AKA Eye]

Don't forget the gravitational interaction between Earth, Venus and the Sun, is ongoing and variable relative to thier locations, not just at transit.That's simply Veus eclipsing the sun from our peespective.The gravities don't go away.
What I realy wanted to say is this.The photo that apeared on apod can be blown up substantialy and in so doing will give the viewer a beautifull view of an "Einsteins' Lense". You will notice the detail on Sun's surface is distorted like a pucker around the perimeter of the Planet..This was a very big treat when I found it But this picture wasn't the source. It was most pronounced in the UV wavelength video taken by the SDO(Solar Dynamics Observatory).In the shots that are highly detailed as the planet passes over the sun's surface the details behind are warped and distorted near the planet's edge.
It's a way cool phenomenea produced by gravity bending the spacetime around the planet and therefor bending the light passing near it. Way cool. Uncle Albert woulda been thrilled. It's also a realy handy way to predict the exact mass of Venus.

[Chris Peterson]

Don't forget the gravitational interaction between Earth, Venus and the Sun, is ongoing and variable relative to thier locations, not just at transit.That's simply Veus eclipsing the sun from our peespective.The gravities don't go away.
What I realy wanted to say is this.The photo that apeared on apod can be blown up substantialy and in so doing will give the viewer a beautifull view of an "Einsteins' Lense". You will notice the detail on Sun's surface is distorted like a pucker around the perimeter of the Planet..This was a very big treat when I found it But this picture wasn't the source. It was most pronounced in the UV wavelength video taken by the SDO(Solar Dynamics Observatory).In the shots that are highly detailed as the planet passes over the sun's surface the details behind are warped and distorted near the planet's edge.
It's a way cool phenomenea produced by gravity bending the spacetime around the planet and therefor bending the light passing near it. Way cool. Uncle Albert woulda been thrilled. It's also a realy handy way to predict the exact mass of Venus.

Whatever you're seeing is some sort of optical aberration. The magnitude of gravitational lensing by Venus is much, much smaller than a single pixel in the image. It isn't visible or measurable.

[Guest]

Have we ever looked at stars other than the sun with a Hydrogen Alpha filter? Would we be able to see a planet transit?

[Chris Peterson]

Have we ever looked at stars other than the sun with a Hydrogen Alpha filter? Would we be able to see a planet transit?

Wide band Ha filters (3-10 nm) are commonly used for astronomical imaging, since ionized hydrogen clouds are interesting. Narrow Ha filters like those used for imaging the Sun (<1 nm) are used for seeing structure, which requires resolving the object. That's not problem with the Sun, but only a handful of stars are large enough and close enough to be resolved, and at that are only a few pixels wide... so there's probably nothing to see with a narrow Ha filter. The few resolvable stars probably cannot be resolved well enough to image a transiting planet, although planetary transits are readily detected photometrically, and several thousand are known using this method.

[neufer]

Click to play embedded YouTube video.