APOD: Venus and the Triply Ultraviolet Sun (2022 Mar 06)

[APOD Robot]

Venus and the Triply Ultraviolet Sun

Explanation: This was a very unusual type of solar eclipse. Typically, it is the Earth's Moon that eclipses the Sun. In 2012, though, the planet Venus took a turn. Like a solar eclipse by the Moon, the phase of Venus became a continually thinner crescent as Venus became increasingly better aligned with the Sun. Eventually the alignment became perfect and the phase of Venus dropped to zero. The dark spot of Venus crossed our parent star. The situation could technically be labeled a Venusian annular eclipse with an extraordinarily large ring of fire. Pictured here during the occultation, the Sun was imaged in three colors of ultraviolet light by the Earth-orbiting Solar Dynamics Observatory, with the dark region toward the right corresponding to a coronal hole. Hours later, as Venus continued in its orbit, a slight crescent phase appeared again. The next Venusian transit across the Sun will occur in 2117.

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[AVAO]

The image of the sun takes 500 seconds to get to us. The image of the black disk of Venus takes 136 seconds, i.e. 364 seconds less. It took Venus 25,200 seconds to cross the disks of the sun for 1,045 million km. The diameter of Venus is 12104 km. i.e. to move the distance of one Venus diameter, Venus needs 292 seconds. However, since the image of Venus arrives 364 seconds later than the image of the sun, Venus was effectively 1.25 times the diameter of Venus to the left when viewing the scene from Earth in 2012!
https://upload.wikimedia.org/wikipedia/ ... 060612.jpg

Interesting to think about reality in astronomical dimensions.
That's why I like rainbow's

P.S. I hope, my calculations are +/- correctly...

[gmPhil]

An interesting book, for those that don't know it, is "Chasing Venus" by Andrea Wulf', chronicling the attempts by' astronomers in the 18thC to measure Venus' two transits across the sun then, which would allow them to work out the distance it was from the Sun, and hence begin to get an idea of the size of the solar system as a whole - something which hitherto had been little more than pure guesswork. It took quite some effort, with numerous poorly prepared expeditions across the globe, not all of which ended well...

[Chris Peterson]

The image of the sun takes 500 seconds to get to us. The image of the black disk of Venus takes 136 seconds, i.e. 364 seconds less. It took Venus 25,200 seconds to cross the disks of the sun for 1,045 million km. The diameter of Venus is 12104 km. i.e. to move the distance of one Venus diameter, Venus needs 292 seconds. However, since the image of Venus arrives 364 seconds later than the image of the sun, Venus was effectively 1.25 times the diameter of Venus to the left when viewing the scene from Earth in 2012!
https://upload.wikimedia.org/wikipedia/ ... 060612.jpg

Interesting to think about reality in astronomical dimensions.
That's why I like rainbow's ;-)

P.S. I hope, my calculations are +/- correctly...

When working with the positions of nearby objects (basically, Solar System objects) we frequently have to consider the impact of motion during the time light is in transit. Astrometry, orbital calculations for planets and asteroids... anything where we're comparing the apparent positions of two or more objects in order to calculate true positions, we need to apply what is known as light-time correction. A related correction is called aberration of light, which corrects for the motion of the observer.

[stargeezer2233]

What struck me most about the 2012 transit of Venus as compared to the many transits of Mercury I have observed is that the edge of Venus was a blur as compared to the sharp edge of Mercury. At first I thought I wasn't getting good focus in my scope until I realized I was seeing the effect of Venus's thick atmosphere!

[orin stepanek]

Nice photo of transit of Venus! First thing that caught my eye was
the dark blue area;(hole)! Is this during a solar cool cyvle?
Also a beautiful photo of the sun!

another picture of solar hole!

Chow time for 9 cats!

[Fred the Cat]

Venus only scores one point in the celestial game of coronal hole.

[Chris Peterson]

What struck me most about the 2012 transit of Venus as compared to the many transits of Mercury I have observed is that the edge of Venus was a blur as compared to the sharp edge of Mercury. At first I thought I wasn't getting good focus in my scope until I realized I was seeing the effect of Venus's thick atmosphere!

I'm very doubtful you were seeing any edge blur due to the atmosphere. The entire atmosphere of Venus, top to bottom, spans only an arcsecond from Earth... seeing, especially in the day, is rarely that good. But only the top few percent at most isn't completely opaque, so we're really talking about a blur that couldn't exceed 10 or 20 milliarcseconds. Totally impossible to see from an earthbound telescope. And indeed, even visible light images of Venus made from craft in orbit around that planet don't show a blurry edge.

I'd say that the difference you saw was the result of a steadier atmosphere during the Mercury transit, nothing to do with Venus's atmosphere. The only studies I've seen of Venus's atmosphere during transits involve the dynamics of Venus's limb crossing the solar limb, where some effects of the atmosphere might possibly be visible for a second or two.

[gmPhil]

I'm very doubtful you were seeing any edge blur due to the atmosphere.

Well.. from my admittedly limited understanding, the thick atmosphere will still distort the image we see from here - you're not seeing the atmosphere per se, but light passing through it will be refracted nonetheless. This, along with the "black drop effect" (eg when you pinch your fingers together in front of a bright light and they seem to connect before they actually do), was why the early measurements of Venus transiting the sun were not as accurate as the astronomers were hoping they'd be, and was also the first clue they had that Venus had an atmosphere at all.
Or such was what I gathered from the book I referred to in my earlier post - but I may well have misunderstood. I make no claims to being an expert in such matters.

[Chris Peterson]

I'm very doubtful you were seeing any edge blur due to the atmosphere.

Well.. from my admittedly limited understanding, the thick atmosphere will still distort the image we see from here - you're not seeing the atmosphere per se, but light passing through it will be refracted nonetheless. This, along with the "black drop effect" (eg when you pinch your fingers together in front of a bright light and they seem to connect before they actually do), was why the early measurements of Venus transiting the sun were not as accurate as the astronomers were hoping they'd be, and was also the first clue they had that Venus had an atmosphere at all.
Or such was what I gathered from the book I referred to in my earlier post - but I may well have misunderstood. I make no claims to being an expert in such matters.

I agree that the atmosphere can change the way light refracts and scatters, which can impact the appearance of the edge. Just that it can't cause any "blurring" resolvable by ground-based telescopes operating in visible light. And the black drop effect is an example of what I was talking about with how the limbs interact.