APOD: 3D 67P (2019 Mar 30)

[APOD Robot]

3D 67P

Explanation: Put on your red/cyan glasses and float next to the jagged and double-lobed nucleus of Churyumov-Gerasimenko, also known as Comet 67P. The stereo anaglyph was created by combining two images from the Rosetta spacecraft's narrow angle OSIRIS camera taken on July 25, 2015 from a distance of 184 kilometers. Numerous jets are emanating from the small solar system world's active surface near its closest approach to the Sun. The larger lobe is around 4 kilometers in diameter, joined to a smaller, 2.5 kilometer diameter lobe by a narrow neck. Rosetta's mission to the comet ended in September 2016 when the spacecraft was commanded to a controlled impact with the comet's surface. Keep those 3D glasses on though. You can check out a new catalog of nearly 1400 stereo anaglyphs created from Rosetta image data on this website.

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[orin stepanek]

Not a whole lot of vapor coming from this comet; most be a low moisture comet! I guess that not all comets are alike. I liked the 3-D picture! Also stereo views show many jagged surfaces on this comet rock!

[Chris Peterson]

For those who prefer not using glasses,
_
Parallel view:

Cross-eyed view:

[orin stepanek]

Cross your eyes and dot your (oops!)

[BDanielMayfield]

Not a whole lot of vapor coming from this comet; most be a low moisture comet!

It's been around a lot. Jupiter has bullied it about quite a bit.

Like the other comets of the Jupiter family, Churyumov–Gerasimenko probably originated in the Kuiper belt and was ejected towards the interior of the Solar System, where later encounters with Jupiter successively changed its orbit.

Up to 1840, the comet's perihelion distance was 4 AU (600 million km), too far for the Sun to vaporize the nucleus. In 1840 Jupiter changed the orbit to a perihelion distance of 3 AU (450 million km), and later encounters further decreased that distance to 2.77 AU (414 million km).[43]

In February 1959, a close encounter with Jupiter[44] moved Churyumov–Gerasimenko's perihelion inward to about 1.29 AU (193 million km), where it remains today.[14][43]

It's not so much that it's a dry comet, but that it only gets close enough to the sun for a light steaming. But its water is extra heavy:

The composition of water vapor from Churyumov–Gerasimenko, as determined by the Rosetta spacecraft, is substantially different from that found on Earth. The ratio of deuterium to hydrogen in the water from the comet was determined to be three times that found for terrestrial water. This makes it unlikely that water found on Earth came from comets such as Churyumov–Gerasimenko.[9][63][64] On 22 January 2015, NASA reported that, between June and August 2014, the comet released increasing amounts of water vapor, up to tenfold as much.

[orin stepanek]

I wonder how much rain we get because of comets? Anybody ever do a study?

[Uncle Jeff]

After seeing APoD for 30 & 31 Mar, I'd like to see the 3D effect on a composite/simulation of a group of galaxies like APod 31-Mar to display relative distances. Has it already been done?

[dromeuf]

I am a team member of this stereoscopic 67P catalogue archive.

Anaglyph stereoscopy is delicate. I advise you to watch these anaglyphs in a dark luminous light ambiance, without luminous reflection on the screen. You can download the high resolution PNG version and do not hesitate to zoom with the mouse wheel for an immersive effect. We must choose a good pair of glasses with the purest red and cyan filters possible so that the image intended for one eye is not injected into the other (otherwise unpleasant vision, crosstalk left-right, the brain crash bug !). You can test your filters with a test pattern here : http://www.david-romeuf.fr/3D/Anaglyphe ... glyph.html . It's very important because unsuitable/bads filters on the glasses can totally degrade the views. We can buy red-cyan viewers for example : American paper optics https://the3dmarket.com/collections/ana ... s-red-cyan , or BEREZIN RED-CYAN https://www.berezin.com/3d/3dglasses.htm .

The catalog presently contains some 1500 anaglyphs and may be extended in the future (on a potential of 4700 stereoscopic pairs in the 27000 images of the ROSETTA mission). The anaglyphs are organized in albums (nucleus components, regions, typical features) and can also be searched using advanced tools. They are first displayed as clickable thumbnails. A first click displays the image with its parameters, a second click displays the image in full size. You can click again to zoom any area. A full documentation is included as well as general recommendations to best view the anaglyphs. More info : https://arxiv.org/abs/1903.02324

There is good and less good in this archive, sometimes very good. In fact, the mission was not intended for real stereoscopy. There were not two cameras on two spacecrafts, which took pictures at the same time (like our eyes for our brain). We do not control the distance between the two shots for hyper stereoscopy ideals parameters (the stereoscopic base / right-left eyes 65-70 mm / 1/30 disparity = 1.8°), the filters of the camera, the target point and especially the images of the couple are not simultaneous.

The problem of two-step images is the most serious because the intrinsic rotation of the comet on itself modifies the projection of the shadows of the "mountains" and structures on the surface of the comet. These shadows move and are incoherents for the brain (they vibrate). When we judged the document interesting, we manually corrected the shadows by transferring the imprint of its largest surface in one of the images of the couple towards its counterpart. This is not a "trick" because the operation is just to turn off light the pixels of the surface that are not lit in the homologous image of the couple. There may be more than one hour of work for some documents, for example, the compositions with the nucleus + the jets and the coma because there is a double thresholding and a methodical cutting.

The problem of the base (or parallax) is less problematic because the brain adapts, except to the extrema, and according to the dimensions of stereo-reproduction. Thus, the anaglyphs that have a big shift red-cyan are rather to look on a small screen (< 1/15 disparity), those who have a very small shift red-cyan are rather for a very large screen (> 1/80 disparity) or to zoom much on the screen computer. Between the two, an ideal parallax of about 2 ° to the nearest object, in the foreground, these anaglyphs are ideal for a computer or TV 3D screen (1/30 disparity).

Nice day and good Sky ! David.

[Nitpicker]

Thank you for all the details, David.

[neufer]

I wonder how much rain we get because of comets?

A famous depiction of the 1833 meteor storm, produced in 1889 for the Seventh-day Adventist book Bible Readings for the Home Circle.

---

<<The Leonids are a prolific November meteor shower associated with the comet Tempel–Tuttle, which are also known for their spectacular meteor storms that occur about every 33 years. Their proper Greek name should be Leontids but the word was initially constructed as a Greek/Latin hybrid and it has been used since.

Earth moves through the meteoroid stream of particles left from the passages of a comet. The stream comprises solid particles, known as meteoroids, ejected by the comet as its frozen gases evaporate under the heat of the Sun when it is close enough – typically closer than Jupiter's orbit. The Leonids are a fast moving stream which encounter the path of Earth and impact at 72 km/s. Larger Leonids which are about 1 cm across have a mass of half a gram and are known for generating bright (apparent magnitude −1.5) meteors. An annual Leonid shower may deposit 12 or 13 tons of particles across the entire planet.

The Leonids are famous because their meteor showers, or storms, can be among the most spectacular. Because of the storm of 1833 and the recent developments in scientific thought of the time, the Leonids have had a major effect on the development of the scientific study of meteors, which had previously been thought to be atmospheric phenomena. Although it has been suggested the Leonid meteor shower and storms have been noted in ancient times, it was the meteor storm of 1833 that broke into people's modern day awareness – it was of truly superlative strength. One estimate of the peak rate is over one hundred thousand meteors an hour, but another, done as the storm abated, estimated in excess of 240,000 meteors during the nine hours of the storm, over the entire region of North America east of the Rocky Mountains.

It was marked by several nations of Native Americans: the Cheyenne established a peace treaty and the Lakota calendar was reset. Abolitionists including Harriet Tubman and Frederick Douglass took note and others. Abraham Lincoln commented on it years later.

Denison Olmsted noted the shower was of short duration and was not seen in Europe, and that the meteors radiated from a point in the constellation of Leo and he speculated the meteors had originated from a cloud of particles in space. Accounts of the 1866 repeat of the Leonids counted hundreds per minute/a few thousand per hr in Europe. It was in 1866–67 that information on Comet Tempel-Tuttle was gathered pointing it out as the source of the meteor shower. When the storms failed to return in 1899, it was generally thought that the dust had moved on and storms were a thing of the past.>>

[neufer]

Click to play embedded YouTube video.

Not a whole lot of vapor coming from this comet; must be a low moisture comet!

It's not so much that it's a dry comet, but that it only gets close enough to the sun for a light steaming. But its water is extra heavy:

The ratio of deuterium to hydrogen in the water from the comet was determined to be three times that found for terrestrial water. NASA reported that, between June and August 2014, the comet released increasing amounts of water vapor, up to tenfold as much.

[neufer]