APOD: Venus and the Triply Ultraviolet Sun (2013 Aug 20)

[APOD Robot]

Venus and the Triply Ultraviolet Sun

Explanation: An unusual type of solar eclipse occurred last year. Usually it is the Earth's Moon that eclipses the Sun. Last June, most unusually, 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 above 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 solar eclipse will occur in 2117.

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[Jim Leff]

Can anyone explain why this is so rare?

[geckzilla]

You could think about it in phases. Every time our moon reaches its new phase, that means it's really close to the sun. It happens about once a month. But you know we don't have lunar eclipses every month and that's because the orbit doesn't always cross directly in front of the sun. Venus does the same thing but it takes 584 days for each cycle and, just like the moon, it doesn't cross the sun every time. So now you can imagine why it's so rare.

[markc]

I had the same question about the rare eclipse event. Does that mean that Earth and Venus orbits are not exactly in the same plane?

[ellishw]

So why is there no mention (that I can find) of "Transit of Venus?" Isn't a "transit" historically a significant event? Here it is referred to as an "eclipse" but is that not the same thing?

[neufer]

I had the same question about the rare eclipse event. Does that mean that Earth and Venus orbits are not exactly in the same plane?

Yes.

Venus comes to inferior conjunction (i.e., a "New Venus") every 584 days
but it doesn't count as a transit unless that conjunction occurs in early June or December when the two planes cross.

[b][color=#0000FF][size=150]Diagram of transits of Venus and the angle between the orbital planes of Venus and Earth[/size][/color][/b]

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<<Venus, with an orbit inclined by 3.4° relative to the Earth's, usually appears to pass under (or over) the Sun at inferior conjunction. A transit occurs when Venus reaches conjunction with the Sun at or near one of its nodes—the longitude where Venus passes through the Earth's orbital plane (the ecliptic)—and appears to pass directly across the Sun. Although the inclination between these two orbital planes is only 3.4°, Venus can be as far as 9.6° from the Sun when viewed from the Earth at inferior conjunction. Since the angular diameter of the Sun is about half a degree, Venus may appear to pass above or below the Sun by more than 18 solar diameters during an ordinary conjunction.

Sequences of transits usually repeat every 243 years. After this period of time Venus and Earth have returned to very nearly the same point in their respective orbits. During the Earth's 243 sidereal orbital periods, which total 88757.3 days, Venus completes 395 sidereal orbital periods of 224.701 days each, equal to 88756.9 Earth days. This period of time corresponds to 152 synodic periods of Venus.

The pattern of 105.5, 8, 121.5 and 8 years is not the only pattern that is possible within the 243-year cycle, because of the slight mismatch between the times when the Earth and Venus arrive at the point of conjunction. Prior to 1518, the pattern of transits was 8, 113.5 and 121.5 years, and the eight inter-transit gaps before the 546 CE transit were 121.5 years apart. The current pattern will continue until 2846, when it will be replaced by a pattern of 105.5, 129.5 and 8 years. Thus, the 243-year cycle is relatively stable, but the number of transits and their timing within the cycle will vary over time. Since the 243:395 Earth:Venus commensurability is only approximate, there are different sequences of transits occurring 243 years apart, each extending for several thousand years, which are eventually replaced by other sequences. For instance, there is a series which ended in 541 BCE, and the series which includes 2117 only started in 1631 AD.>>

[neufer]

So why is there no mention (that I can find) of "Transit of Venus?"
Isn't a "transit" historically a significant event?
Here it is referred to as an "eclipse" but is that not the same thing?

Because of the sequester APOD could not afford to buy the letters to spell "transit."
-------------------------------------------------------------------------------------------------
Ugarte (Peter Lorre): Look, Rick. Know what this is?

• Something that even you have never seen.
  Letters of transit signed by General de Gaulle.
  Cannot be rescinded. Not even questioned.
  Tonight I'll be selling those for more money than I ever dreamed of.
  And then, adios, Casablanca.

<<An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. An eclipse is a type of syzygy. The word "transit" refers to cases where the nearer object appears considerably smaller than the more distant object. Cases where the nearer object appears larger and completely hides the more distant object are known as occultations.

A syzygy (from the Ancient Greek suzugos (σύζυγος) meaning, “yoked together”.) is a straight-line configuration of three celestial bodies in a gravitational system. Solar and lunar eclipses occur at times of syzygy, as do transits and occultations. The term is often applied when the Sun and Moon are in conjunction (new moon) or opposition (full moon).

Eclipse is derived from the ancient Greek noun ἔκλειψις (ékleipsis), which means "the abandonment", "the downfall", or "the darkening of a heavenly body", which is derived from the verb ἐκλείπω (ekleípō) which means "to abandon", "to darken", or "to cease to exist," a combination of prefix ἐκ- (ek-), from preposition ἐκ (ek), "out," and of verb λείπω (leípō), "to be absent". The term eclipse is most often used to describe either a solar eclipse, when the Moon's shadow crosses the Earth's surface, or a lunar eclipse, when the Moon moves into the Earth's shadow. However, it can also refer to a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its host planet, or a moon passing into the shadow of another moon. A binary star system can also produce eclipses if the plane of the orbit of its constituent stars intersects the observer's position.>>

[Psnarf]

It is so convenient having a star close enough to study in such detail. Magnetic coronal loops, a coronal hole so close you can peek inside (using a satellite from a safe distance), can't see that stuff on other stars. It staggers my imagination to know that the loops are only visible in the ultraviolet frequencies. Multiply ionized iron at two million degrees Kelvin formed by the fusion of silicon?
http://www.flickr.com/photos/pldove/716 ... otostream/
I've read that the layers of elements from fusion just before supernovae starts with iron at the center from silicon fusion, silicon from magnesium fusion, magnesium from neon fusion, neon from oxygen fusion, oxygen from carbon fusion which is from helium fusion, with hydrogen at the outermost layer. I did not know that there was iron near the surface, thought the magnetic lines of force were generated from the motion of electrons. The presence of iron suggests there is Si, Mg, Ne, O, and C in there somewhere, unless it is the product of fission reactions. I learn a lot at apod.com, particularly how vast there is yet to learn.

[neufer]

It is so convenient having a star close enough to study in such detail.

There was another good reason as well but it skips my mind for the moment.

[Boomer12k]

Whoa.....now I know where "Paisley" comes from in the sixties.....Psychedelic. Wow...Flashback....Trippin'.....Far Out....Out of Sight, Man....

:---[===] *

[Ann]

It is so convenient having a star close enough to study in such detail.

There was another good reason as well but it skips my mind for the moment.

Yes... like... the energy that keeps life going on the Earth... there is Earth's internal heat... is there another energy source, too?

Can't remember...

Ann

[geckzilla]

I'm pretty sure it's just there so that past humans could worship and adore it and spawn many religions inspired by its greatness.

[SevenEagles]

What is one crazy photograph.

[Beyond]

Ya know... it does sorta resemble a cheese pizza (with one anchovy) that's been sitting around for q-u-i-t-e a while. Toooo many things growing there.

[BDanielMayfield]

Whoa.....now I know where "Paisley" comes from in the sixties.....Psychedelic. Wow...Flashback....Trippin'.....Far Out....Out of Sight, Man....

:---[===] *

Maybe that should be ‘Venus and the Trippy Ultraviolet Sun.’

[Anthony Barreiro]

It is so convenient having a star close enough to study in such detail. Magnetic coronal loops, a coronal hole so close you can peek inside (using a satellite from a safe distance), can't see that stuff on other stars. It staggers my imagination to know that the loops are only visible in the ultraviolet frequencies. Multiply ionized iron at two million degrees Kelvin formed by the fusion of silicon?
http://www.flickr.com/photos/pldove/716 ... otostream/
I've read that the layers of elements from fusion just before supernovae starts with iron at the center from silicon fusion, silicon from magnesium fusion, magnesium from neon fusion, neon from oxygen fusion, oxygen from carbon fusion which is from helium fusion, with hydrogen at the outermost layer. I did not know that there was iron near the surface, thought the magnetic lines of force were generated from the motion of electrons. The presence of iron suggests there is Si, Mg, Ne, O, and C in there somewhere, unless it is the product of fission reactions. I learn a lot at apod.com, particularly how vast there is yet to learn.

The Sun is a Population I star. That means old Sol is a member of the most recent population of stars and contains small amounts of elements heavier than Hydrogen and Helium that were formed in earlier Population II stars, some of which went supernova before he was born. He's a middle-aged main-sequence star, fusing Hydrogen into Helium, nothing more exotic happening yet. 71% Hydrogen, 27% Helium, 1% Oxygen, 0.4% Carbon, and a mere sprinkling of all the other elements.

This is a truly awesome picture. Watching this transit of Venus from a beach on O'ahu is a cherished memory, although it didn't appear quite so psychedelic. Maybe I didn't take enough of the right kinds of drugs.

Like many other deities, the Sun is best admired from the right distance.

[BMAONE23]

Perhaps you should have been on Maui

[FloridaMike]

Have to get this printed on black velvet, off to Bing we go ....

[Star Geezer]

Why is Venus not on the 9:00 -3:00 horizontal axis in the photograph?
In other words, on the ecliptic plane.

[JohnD]

We haven't mentione that Venus transits occur in pairs, eight years apart. The last before the 2012 transit was in 2004, when I watched it while on holiday in France. The other, mainly French, inhabitants of my camp site were amused by the crazy Englishman with his binoculars on a camera stand, peering at a piece of white card in his hand. But when they came to see, they stayed to enjoy! Excited, intrigued French people were more than I could cope with linguisticly!

But my memory is that the globe of Venus was much smaller on the Sun than appears in this image. A quick search for "Transit of Venus"inages confirms this. But is this an illusion of the large image shown in this APOD?

JOhn

[cindy4444]

This was a year ago June and not last June. Interesting to hear the transit described as an eclipse. I enjoyed seeing it and sorry no one alive now will have the chance again. In connection with viewing it, I did a lot of studying of the orbits and planes for Earth and Venus' orbit. Interesting that they cross in the same plane only in June and December and precession has not changed this in centuries?

[Anthony Barreiro]

Why is Venus not on the 9:00 -3:00 horizontal axis in the photograph?
In other words, on the ecliptic plane.

The motions of the planets in our solar system are not that simple.

During this transit Venus was slightly north of the ecliptic as seen from Earth, and her orbit is slightly inclined relative to Earth's orbit. So she did not cross the diameter of the Sun as seen from Earth, rather she traveled across a shorter chord from the Sun's northwest limb to the Sun's east-northeast limb (I'm using west for the Sun's left-hand limb as seen from Earth and east for the Sun's right-hand limb as seen from Earth; the diagram below uses the opposite convention).



You could think of this as being analogous to a partial solar eclipse, during which the Moon cross the face of the Sun north of the ecliptic.

A further slight complication arises from the fact that the ecliptic doesn't pass exactly from east to west across the face of the Sun. Depending on the time of the year and your location on the surface of the Earth, the ecliptic will pass a bit north or south of due east and a bit south or north of due west. I'm sure there must be a moment and a location when the ecliptic passes exactly east to west across the face of the Sun, but I don't know when and where.

[neufer]

But my memory is that the globe of Venus was much smaller on the Sun than appears in this image. A quick search for "Transit of Venus" images confirms this. But is this an illusion of the large image shown in this APOD?

June "Transits of Venus" images are slightly smaller than December "Transits of Venus"
because they represent the aphelion & perihelion of the Earth's orbit respectively.

[neufer]

I enjoyed seeing it and sorry no one alive now will have the chance again. In connection with viewing it, I did a lot of studying of the orbits and planes for Earth and Venus' orbit. Interesting that they cross in the same plane only in June and December and precession has not changed this in centuries?

The first known observations and recording of a transit of Venus were made on 4 December 1639 by the English astronomers Jeremiah Horrocks and his friend and correspondent William Crabtree. The next transit of Venus will be 10–11 December 2117 when my granddaughter (who just celebrated her first birthday today) will be 105 (or just 9 years older than my mother who will be 96 in 7 weeks).

[Buddy]

At first I thought it was a minor satellite of Jupiter transiting Io. The sun looks so different in UV!