APOD: The Cat's Eye Nebula in Optical and... (2021 Nov 07)

[APOD Robot]

The Cat's Eye Nebula in Optical and X-ray

Explanation: To some it looks like a cat's eye. To others, perhaps like a giant cosmic conch shell. It is actually one of brightest and most highly detailed planetary nebula known, composed of gas expelled in the brief yet glorious phase near the end of life of a Sun-like star. This nebula's dying central star may have produced the outer circular concentric shells by shrugging off outer layers in a series of regular convulsions. The formation of the beautiful, complex-yet-symmetric inner structures, however, is not well understood. The featured image is a composite of a digitally sharpened Hubble Space Telescope image with X-ray light captured by the orbiting Chandra Observatory. The exquisite floating space statue spans over half a light-year across. Of course, gazing into this Cat's Eye, humanity may well be seeing the fate of our sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.

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[VictorBorun]

It's pretty much symmetric, with the center in the progenitor star.
What if we make a stereo using 180° rotation for one eye?
Here is my try, with -65° rotation for sort of fitting.
Not good enough

[madtom1999]

Is it possible to run a spectrograph over this to get the velocities of the gasses in the nebula and so more fully understand its shape?

[Fred the Cat]

If this is a cat's eye, the kitten's eye looks to grow up in the years to follow.

[orin stepanek]

APOD is not well understood.

Don't understand either; but a very beautiful Nebula indeed! Life
there,( if any,) must have ended quite quickly!

Almost hypnotic!

Outer shells also very intricate and beautiful!

[johnnydeep]

Fun fact: per https://www.universeguide.com/nebula/catseyenebula, the Cat's Eye Nebula is almost exactly 1000 parsecs away at 3262 ly. A parsec is 3.26156 ly.

[ PS - yes, I know that figure of 3262 ly distance for the nebula is suspiciously way too accurate. Perhaps somebody really wanted it to be exactly 1000 parsecs! ]

[neufer]

Fun fact: per https://www.universeguide.com/nebula/catseyenebula, the Cat's Eye Nebula is almost exactly 1000 parsecs away at 3262 ly. A parsec is 3.26156 ly. [ PS - yes, I know that figure of 3262 ly distance for the nebula is suspiciously way too accurate. Perhaps somebody really wanted it to be exactly 1000 parsecs! ]

Is it possible to run a spectrograph over this to get the velocities of the gasses in the nebula and so more fully understand its shape?

<<Planetary nebulae distances like NGC 6543 are generally very inaccurate and not well known. Some recent Hubble Space Telescope observations of NGC 6543 taken several years apart determine its distance from the angular expansion rate of 3.457 milliarcseconds per year. Assuming a line of sight expansion velocity of 16.4 km/s, this implies that NGC 6543's distance is 1001±269 parsecs away from Earth. Several other distance references, like what is quoted in SIMBAD in 2014 based on Stanghellini, L., et al. (2008) suggest the distance is 1623 parsecs.

The angular expansion of the nebula can also be used to estimate its age. If it has been expanding at a constant rate of 10 milliarcseconds a year, then it would take 1000±260 years to reach a diameter of 20 arcseconds. This may be an upper limit to the age, because ejected material will be slowed when it encounters material ejected from the star at earlier stages of its evolution, and the interstellar medium.>>

<<In the Mawlawiyyah order of Sufi Islam, a novice must complete 1001 days of prayer before becoming a dada, or junior teacher of the faith. In many cases, including the title "Thousand and One Nights", 1001 is meant to indicate a "big number", and need not be taken literally.

In The Book of One Thousand and One Nights, Scheherazade tells her husband the king a new story every night for 1,001 nights, staving off her execution. From this, 1001 is sometimes used as a generic term for "a very large number", starting with a large number (1000) and going beyond it. In Arabic, this is usually phrased as "one thousand things and one thing", e.g.: The Book of One Thousand and One Nights, in Arabic Alf layla wa layla (Arabic: ألف ليلة و ليلة‎), literally "One thousand nights and a night".

Scheherazade numbers are a set of numbers identified by Buckminster Fuller in his book Synergetics. Fuller does not give a formal definition for this term, but from the examples he gives, it can be understood to be those numbers that contain a factor of the primorial n#, where n≥13 and is the largest prime factor in the number. Fuller called these numbers Scheherazade numbers because they must have a factor of 1001.>>

[johnnydeep]

Fun fact: per https://www.universeguide.com/nebula/catseyenebula, the Cat's Eye Nebula is almost exactly 1000 parsecs away at 3262 ly. A parsec is 3.26156 ly. [ PS - yes, I know that figure of 3262 ly distance for the nebula is suspiciously way too accurate. Perhaps somebody really wanted it to be exactly 1000 parsecs! ]

<<Planetary nebulae distances like NGC 6543 are generally very inaccurate and not well known. Some recent Hubble Space Telescope observations of NGC 6543 taken several years apart determine its distance from the angular expansion rate of 3.457 milliarcseconds per year. Assuming a line of sight expansion velocity of 16.4 km/s, this implies that NGC 6543's distance is 1001±269 parsecs away from Earth. Several other distance references, like what is quoted in SIMBAD in 2014 based on Stanghellini, L., et al. (2008) suggest the distance is 1623 parsecs.

The angular expansion of the nebula can also be used to estimate its age. If it has been expanding at a constant rate of 10 milliarcseconds a year, then it would take 1000±260 years to reach a diameter of 20 arcseconds. This may be an upper limit to the age, because ejected material will be slowed when it encounters material ejected from the star at earlier stages of its evolution, and the interstellar medium.>>

Apparently Hubble can use a refined parallax measurement technique called "spatial scanning" that is supposedly accurate to about 10000 ly. But I don't understand how it works. This article didn't help - https://www.nasa.gov/press/2014/april/n ... nto-space/

To make a distance measurement, two exposures of the target Cepheid star were taken six months apart, when Earth was on opposite sides of the sun. A very subtle shift in the star's position was measured to an accuracy of 1/1,000 the width of a single image pixel in Hubble's Wide Field Camera 3, which has 16.8 megapixels total. A third exposure was taken after another six months to allow for the team to subtract the effects of the subtle space motion of stars, with additional exposures used to remove other sources of error.

There has got to be something more to it than is described here however.

[neufer]

Apparently Hubble can use a refined parallax measurement technique called "spatial scanning" that is supposedly accurate to about 10000 ly. But I don't understand how it works. This article didn't help - https://www.nasa.gov/press/2014/april/n ... nto-space/

To make a distance measurement, two exposures of the target Cepheid star were taken six months apart, when Earth was on opposite sides of the sun. A very subtle shift in the star's position was measured to an accuracy of 1/1,000 the width of a single image pixel in Hubble's Wide Field Camera 3, which has 16.8 megapixels total. A third exposure was taken after another six months to allow for the team to subtract the effects of the subtle space motion of stars, with additional exposures used to remove other sources of error.

There has got to be something more to it than is described here however.

The Gaia spacecraft successfully uses "spatial scanning" in order to determine stellar positions to an accuracy of 6.7 micro-arcseconds (and with relatively small 1.45 × 0.5 m primary mirrors). In essence, a moving "video" of stars tracking linearly across a large array of "fat" pixels is analyzed statistically in order to obtain the best fit for moving point sources. Initially, Gaia was to use interferometry to accurately locate stars but "spatial scanning" turned out to be a superior strategy.

[johnnydeep]

Apparently Hubble can use a refined parallax measurement technique called "spatial scanning" that is supposedly accurate to about 10000 ly. But I don't understand how it works. This article didn't help - https://www.nasa.gov/press/2014/april/n ... nto-space/

To make a distance measurement, two exposures of the target Cepheid star were taken six months apart, when Earth was on opposite sides of the sun. A very subtle shift in the star's position was measured to an accuracy of 1/1,000 the width of a single image pixel in Hubble's Wide Field Camera 3, which has 16.8 megapixels total. A third exposure was taken after another six months to allow for the team to subtract the effects of the subtle space motion of stars, with additional exposures used to remove other sources of error.

There has got to be something more to it than is described here however.

The Gaia spacecraft successfully uses "spatial scanning" in order to determine stellar positions to an accuracy of 6.7 micro-arcseconds (and with relatively small 1.45 × 0.5 m primary mirrors). In essence, a moving "video" of stars tracking linearly across a large array of "fat" pixels is analyzed statistically in order to obtain the best fit for moving point sources. Initially, Gaia was to use interferometry to accurately locate stars but "spatial scanning" turned out to be a superior strategy.

Thanks. "Statistics: is there nothing they can't do?"

A Wikipedia page about spatiospectral scanning has a little more info:

Spatio-spectral scanning[1] is one of four techniques for hyperspectral imaging, the other three being spatial scanning,[2] spectral scanning [3] and non-scanning, or snapshot hyperspectral imaging.

The technique was designed to put into practice the concept of 'tilted sampling' of the hyperspectral data cube, which had been deemed difficult to achieve.[4] Spatio-spectral scanning yields a series of thin, diagonal slices of the data cube. Figuratively speaking, each acquired image is a 'rainbow-colored' spatial map of the scene. More precisely, each image represents two spatial dimensions, one of which is wavelength-coded. To acquire the spectrum of a given object point, scanning is needed.

Spatio-spectral scanning combines some advantages of spatial and spectral scanning: Depending on the context of application, one can choose between a mobile and a stationary platform. Moreover, each image is a spatial map of the scene, facilitating pointing, focusing, and data analysis. This is particularly valuable for irregular or irretrievable scanning movements. Being based on dispersion, spatio-spectral scanning systems yield high spatial and spectral resolution.

The reference leads to a paper about "hyper-spectral and multi-spectral" imaging, which seems to be a related, and perhaps an even more accurate method than plain old "spatial scanning": https://cdn2.hubspot.net/hub/145999/doc ... al ima.pdf

Turns out there's lots more to be found googling for "gaia spatial scanning"...