Favorite APOD

[harry]

I like

http://antwrp.gsfc.nasa.gov/apod/ap050511.html

[orin stepanek]

I may as well get it right. The most beautiful planet.
http://antwrp.gsfc.nasa.gov/apod/ap051224.html
Orin

[S. Bilderback]

I'm a Mac OS/X user, I have over 300 wonderful photos, mostly from APOD and NASA. If you haven't seen the screen saver app. for the Mac it's great, it can do a continuous pans and fades between pictures - it's like having an astronomy movie running on my desk.

Editorial:

Unix rules!

[devany]

Nice thread, how about

http://antwrp.gsfc.nasa.gov/apod/ap980129.html
or
http://antwrp.gsfc.nasa.gov/apod/ap961225.html

but really, my favorite (on APOD) is:
http://antwrp.gsfc.nasa.gov/apod/ap000102.html

Though I prefer the same picture uncropped at:
http://photojournal.jpl.nasa.gov/catalog/PIA00452

Regards

[orin stepanek]

http://antwrp.gsfc.nasa.gov/apod/ap000510.html

This one is really interesting. Notice how smooth the surface is.

Orin

[Crowbar]

This one has been my desktop wallpaper quite a few times:
http://antwrp.gsfc.nasa.gov/apod/ap051217.html

[astroton]

http://antwrp.gsfc.nasa.gov/apod/ap021109.html

This is one of the best surely. Hard to pick up any from so many nice images.

Try this,

http://antwrp.gsfc.nasa.gov/apod/ap041128.html

Try this for light, (amazing, it's only light and our imaginative thoughts that could reach far crners of universe)

http://antwrp.gsfc.nasa.gov/apod/ap021007.html

[BMAONE23]

ASTROTON
This one was released 2 days after the first link in your previous post.

http://antwrp.gsfc.nasa.gov/apod/ap021111.html

It was taken by the 4 meter telescope in your above mentioned link.

I wait in wonder to see the same section of sky imaged be the soon to be built, 100 meter OWL.

[astroton]

for that matter, I don't know if this one has ever been in APOD.

http://hubblesite.org/gallery/album/ent ... r2005036a/

But, It deserves space in APOD to celebrate,

1. Sirius B was theorised (Due to purturbations in Sirius A's path in the space) before, it's presence was ever detected. Victory of theory on deep space.

2. As yet another proof that the nature has given capacity to human brain to wonder about its secrets and it's ready to give them away.

[orin stepanek]

makes a beautiful background!
Orin

http://antwrp.gsfc.nasa.gov/apod/ap060316.html

[Martin]

One of my most recent favorites is:

http://antwrp.gsfc.nasa.gov/apod/ap060113.html


Mostly because the center of a galaxy is always the most difficult to view.

[kovil]

Mucho thanks to all who listed their faves !!!

Me too loves, Sombrero, Andromeda, the incredible Moons of many planets, and the Earth photos from afar, the last Men on our Moon in 1972! - it brings emotions of what we can do as a species, and how sad it is that we also do things like war.

this is one of my faves, as it also has great links.

http://antwrp.gsfc.nasa.gov/apod/ap050403.html

Did you see the Yahoo News article yesterday,(and probably elsewhere too) It is relevant to the Galactic Center Radio Arc photo subject; as well as the Astrophysical Journal article afterwards in this post.
My apologies for posting so much stuff, but I figure if the spammers demand so much space . . . !

The Asterisk Cafe is certainly serving a lot of spam these days !!


===


Cosmic 'DNA': Double Helix Spotted in Space ; Bjorn Carey
SPACE.com Staff Writer
SPACE.com
1 hour, 40 minutes ago


Magnetic forces at the center of the galaxy have twisted a nebula into the shape of DNA, a new study reveals.

The double helix shape is commonly seen inside living organisms, but this is the first time it has been observed in the cosmos.

"Nobody has ever seen anything like that before in the cosmic realm," said the study's lead author Mark Morris of UCLA. "Most nebulae are either spiral galaxies full of stars or formless amorphous conglomerations of dust and gas , space weather. What we see indicates a high degree of order."

These observations, made with NASA's Spitzer Space Telescope, are detailed in the March 16 issue of the journal Nature.

The DNA nebula is about 80 light-years long. It's about 300 light-years from the supermassive black hole at the center of the Milky Way. The nebula is nearly perpendicular to the black hole, moving out of the galaxy at a quick clip—about 620 miles per second (1,000 kilometers per second).

Magnetic field lines at the galactic center are about 1,000 times stronger than on Earth. They run perpendicular to the black hole, but parallel through the nebula. Scientists think that twisting of these lines is what causes the double helix shape.

While the black hole might be the first culprit to come to mind, it's more likely that the magnetic field lines are anchored to a giant gas disk that orbits the black hole several light-years away, researchers say.

It's like having two strands of rope connected to a fixed point, Morris said. As you spin the strands, they braid around each other in a double helix fashion. In this case the gas and dust of the nebula makes up the strands.

"It's as if there's a bar across the middle [of the black hole], or a dumbbell shape, where the strands are anchored, and as it spins around, it twists the strands together," Morris told SPACE.com.

This process takes a long time, though, since the disk completes one orbit around the black hole roughly every 10,000 years. But that's an important number. "Once every 10,000 years is exactly what we need to explain the twisting of the magnetic field lines that we see in the double helix nebula," Morris said.

The recipe for a DNA nebula is strict but simple. It requires a strong magnetic field, a rotating body, and a nebulous cloud of material positioned just right.

Massive central black holes are the best sources for both the strong magnetic field and rotating body, and since most large galaxies have them, Morris expects DNA-like nebula may be common through out the universe.

"I absolutely expect to see [this configuration] in gas-rich galaxies with all these elements in place," Morris said.

However, these nebulas are tough to spot, and current technology limits scientists' observations to our galaxy.


=== Astrophysical Journal ; redaction of infered theory ===JPM post


MHD as DNA in the ISM . . .haha . .
by: geofens 03/15/06 06:28 pm
Msg: 179308 of 179349

Here's the gist if you decline to wade through all the blah blah;

Large scale magnetic fields generated by the intense gravity-wells (black holes) at galactic centers, are thought to influence how the material further out organizes itself into spiral arm structures.

The flux, or dynamics of the field fluctuation, finds harmonics in the scale magnitude. This is why spiral arms and other repetitive structures appear in galactic formations !!

It is not because the material is drawing in by gravity and organizes itself into these patterns, as was initially thought by most everybody.

The magnetic flux and subsequent organization by field line strengths actually slows down gravity's agenda of 'everything all in one place', and gives the Universe even more time for contemplation and the invention of a wide diversity of life forms to populate this vast 'stage of all the worlds', in which we are merely requisite players.

All of this is a complex interaction; the fields organize the extremely light H I, gravity later draws this diffuse material into and forms the denser arm structures along the field strength lines. This presence of the fields gently sets the stage for the arms to form later on. It also takes a while for the gravity-well to form in the galactic center, so galaxies begin without the early benefit of the MHD in the ISM. (magneto-hydro-dynamic, inter-stellar medium)

A brief excerpt was posted yesterday, but today's Yahoo News has the preceeding post on its wire. I thought a much further in depth rendition of that article was worthy of a repost today, as these two articles play together well. Cheers !! ) [ i may be a little out to lunch as HI is neutral and not magnetically reactive? or is the ISM mostly magnetically effectable? ]

=====APJ ; reprint

Multiwavelength Structural Manifestations of Fast Magnetohydrodynamic Density Waves in Spiral Galaxies

In a spiral galaxy, disks of stars and of magnetized interstellar medium (ISM) are dynamically coupled by gravity. The theory of magnetohydrodynamic (MHD) density waves in such a composite rotating disk system provides a basic framework for studying large-scale dynamics and multiwavelength diagnostics of galactic structures. As swirl-like, trailing spiral structures with broad, fuzzy arms (regular or irregular) manifest in neutral hydrogen H I ( H I - hydrogen: one proton with one electron, and at its lowest energy state) disks that are usually larger than optical spiral patterns in disk galaxies, spiral MHD density waves in H I gas disks should persist within and beyond optical patterns. Sporadic diffusions of relativistic cosmic-ray electrons beyond optical patterns may cause radio continuum arms to occasionally extend across optical spiral patterns and correlate with H I spiral arms at larger radii. We here report the first H I observations of the southern spiral galaxy NGC 2997 to support the fast MHD density wave (FMDW) scenario and to confirm the prior prediction that the isolated, polarized radio continuum arm discovered in the southeast quadrant is indeed associated with a broad segment of the H I arm.

For multiwavelength observations of spiral galaxies, we emphasize the important perspective that large-scale magnetic fields of MHD density waves play the key role in organizing correlated spiral structures of the various underlying ISM components. Meanwhile, we briefly discuss the nature of circumnuclear structures of NGC 2997 in reference to those of NGC 1097.

The southern spiral galaxy NGC 2997 was observed recently in both total and polarized radio continuum bands by Han et al. (1999) using the data from the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). Except for the absence of a close companion and other minor differences, NGC 2997 appears strikingly similar to the northern grand-design spiral galaxy M51 with both total and polarized radio continuum ridges tracking along the inner edges of optical spiral arms and with a largely flat rotation curve. What makes NGC 2997 somewhat unusual in radio continuum emissions is the existence of an extended, yet isolated "magnetic arm," without apparent optical or dust counterparts in the southeast quadrant. The lack of H I observations for NGC 2997 makes this isolated majestic arm feature mysterious.

By comparing the radio continuum observations with available multiwavelength observations of M51 and IC 342, Lou et al. (1999) identified the large-scale spiral pattern of NGC 2997 with fast magnetohydrodynamic (MHD) density waves (FMDWs) characterized by grossly in-phase spiral enhancements of stellar and gas densities as well as random and regular magnetic fields. In a late-type spiral galaxy such as NGC 2997, sustained cloud and star formation activities within the optical spiral pattern consume H I gas gradually and systematically. While effectively disrupting regular magnetic fields, hierarchical and concurrent star formation processes along high-density H I gas arms tend to enhance small-scale random magnetic fields via MHD turbulence of the interstellar medium (ISM). By a profusion of relativistic cosmic-ray electrons trapped in the galactic disk plane, structures of random and regular magnetic fields can be detected in total and polarized radio continuum bands, respectively. As a result, manifestations of total and polarized radio continuum emissions may, to various extents, compete with each other along H I gas arms of a FMDW pattern. For a multiband structural study of a spiral galaxy, H I observations are indispensable, providing valuable information about kinematics and the atomic phase of the ISM. Moreover, in the FMDW scenario, H I observations of NGC 2997 are crucial in unraveling the origin of the isolated "magnetic arm" in the southeast quadrant.

For a slow MHD density wave (SMDW) pattern, spiral enhancements of H I gas density and magnetic field are phase-shifted significantly so that the total and polarized radio continuum patterns interfere less, as in the case of NGC 6946.

2. THE SCENARIO OF GALACTIC MHD DENSITY WAVES

The distribution of the massive (hypothetical) dark-matter halo, dominates the large-scale dynamics of a disk galaxy such as NGC 2997, controlling the grossly flat rotation curve of the stellar and gas disks and helps suppress violent bar-type instabilities in the composite disk system. (Dark matter is an invention to explain observational data not explained by current theories)
Analyses of the problem of dynamics started with the theory of hydrodynamic density waves in the stellar disk and with the MHD of the ISM being relegated to a passive role. In essence, stellar velocity dispersion, epicyclic oscillations, and self-gravity together lead to spiral density wave patterns in a thin stellar disk with differential rotation.

Meanwhile, there has been growing evidence for nontrivial ISM roles on theoretical and observational grounds. Dynamically, the magnetized H I disk is an integral component in the overall MHD density wave scenario. The inclusion of the MHD effect on the ISM disk represents a significant development in the density wave scenario and offers a physical perspective for various processes that lead to ISM emissions in different electromagnetic wave bands. In the MHD density wave scenario, coplanar perturbations in the stellar disk, described by the hydrodynamic equations, and coplanar perturbations in the magnetized ISM disk, described by the MHD equations, are effectively coupled through gravity, dictated by the Poisson equation. Along with stellar density waves, ISM sound speed, epicyclic oscillations, Lorentz force, and self-gravity jointly give rise to FMDWs and SMDWs in the magnetized ISM disk. For FMDWs, spiral enhancements of magnetic field and ISM gas density are in-phase, whereas for SMDWs, these two enhancements are significantly phase-shifted.

In both cases, enhancements of surface mass densities in the stellar and magnetized ISM disks remain more or less locked in phase. Consequently, diagnostic features of stellar and MHD density waves are intricately intertwined. Especially for large-scale multiband observations of spiral galaxies, it is absolutely necessary to incorporate the large-scale MHD of the ISM, because the allowed dynamic freedoms of the two different wave modes of FMDWs and SMDWs in a magnetized ISM disk may lead to qualitatively different structural appearances in multiband observations. Besides the red light and near-infrared (NIR) bands that reveal spiral arms of older stars, almost all other diagnostics involve collective pattern manifestations of subprocesses in the magnetized ISM. While we distinguish the dynamics and the diagnostics of the magnetized ISM, the MHD density wave scenario actually provides the basis and the conceptual link for both, with the radiative diagnostics involving wide-range ISM physics which is both comprehensive and complex.

Empirically, the H I spiral pattern often appears larger than the optical pattern in a spiral galaxy (Figs. 1b and 1d). By geometric convergence, the strength of spiral MHD density waves in a H I gas disk tends to be stronger at smaller radii. When certain "critical conditions" are met to trigger cloud and star formation activities at smaller scales, an optical spiral pattern gradually emerges from the underlying high-density H I spiral arms. Consumed by star formation, H I gas becomes gradually depleted in the region occupied by the optical pattern. Although less numerous and efficient, young stars are still born continuously along high-density H I gas arms that extend beyond the conventional optical pattern. Parallel to optical appearances, a trailing H I spiral structure at larger radii may appear as either grand-design, broad and fuzzy, or flocculent.

3. H I OBSERVATIONS OF NGC 2997 AT ATCA

Six separate 12 hr observations of NGC 2997 were carried out at the ATCA (with 0.750 km, 1.5 km, and 6.0 km configurations) between 1995 October 27 and 1996 February 22, using the six-telescope array with a maximum baseline of 6 km. The right ascension and declination (J2000) of the pointing center are 09h45m483 and -311328, respectively. The bandwidth used was 8 MHz divided into 512 × 15.625 kHz channels, with a channel velocity resolution of 3.3 km s-1 centered on 1.415 GHz. The channel map cell size and area are 45 × 45 and 150 × 141, respectively. The primary ATCA calibrator, PKS B1934-638, was observed before each 12 hr run, and these observations were also utilized to calibrate the bandpass.

Each 12 hr run consisted of alternate scans of 45 minutes on NGC 2997 and 3 minutes on the phase and secondary amplitude calibrator PKS B0823-500, with a flux density of 5.0 ± 0.3 Jy at 1.4 GHz. This set of observations suffered little interference, with very few time ranges being deleted from the data set. With calibration and drive times, the total integration time on NGC 2997 actually reduces to 48 hr. The individual u, v databases were processed using the MIRIAD package. Both linear polarizations for each of the 15 baselines for each data set were carefully examined and edited. After amplitude, phase, and bandpass calibrations, continuum subtraction of each database was performed in the complex visibility domain by subtracting first-order, least-square fits to the line-free channels on either side of the NGC 2997 velocity range. The original integration period of 15 s was extended to 60 s by averaging, without incurring time smearing effect. Doppler corrections were applied to align the data sets in a common heliocentric reference frame, and the data were then combined in the u-v plane. (whew !)

H I imaging analysis was performed using the Invert program in the MIRIAD package (Sault & Killeen 1996). The same observing and analysis methods were applied to NGC 289 earlier by Walsh et al. (1997). The data were averaged into channels with a velocity separation of 5.0 km s-1 and a data cube was produced using a robust weighting procedure, with a robustness parameter being -1.0 and with a symmetric taper chosen to emphasize structures of 15 scale. Individual planes in the data cube were CLEANed until the absolute maximum residual decreased to 2.5 times the noise level.

Constructed from a primary FWHP beam of 33, the resulting data cube has a synthesized beam size with a FWHM of 44 × 23, corresponding to 2.6 × 1.3 kpc and with a position angle of -47 (Figs. 1b1d). The average noise, measured in the emission-free regions of the 50 channels that encompass H I signal of NGC 2997, appears Gaussian, with a channel-averaged rms of 2.0 mJy beam-1 (0.4 K). This is comparable to the "theoretical" value of 1.4 mJy beam-1, which excludes confusing sources in the beam. The 3 detection threshold is 2.4 × 1019 atoms cm -2 for each channel in the final data cube.

======
i rest my case

[orin stepanek]

I was browsing and found this. http://antwrp.gsfc.nasa.gov/apod/ap031208.html
Orin

[astroton]

Nice one Orin

I think I will have to add this one now.

http://antwrp.gsfc.nasa.gov/apod/ap060412.html

Many will agree

[harry]

Hello all

The Perseus Cluster of Galaxies

at 250 million light years away

http://antwrp.gsfc.nasa.gov/apod/ap051230.html

its main centre galaxy

http://www.rdelsol.com/RC20/RC_GALAXIES/NGC1275_FC.jpg

[starnut]

What about this?

http://antwrp.gsfc.nasa.gov/apod/ap051004.html

Imagine yourself floating somewhere far from the solar system, looking towards the Galactic Center!

[harry]

Hello nutty star

Our Milky Way Bar kid
and this
http://antwrp.gsfc.nasa.gov/apod/ap040411.html
http://antwrp.gsfc.nasa.gov/apod/ap050403.html
http://antwrp.gsfc.nasa.gov/apod/ap051023.html
http://www.space.com/scienceastronomy/a ... 20111.html
http://antwrp.gsfc.nasa.gov/apod/ap041106.html
http://antwrp.gsfc.nasa.gov/apod/ap041107.html
http://antwrp.gsfc.nasa.gov/apod/ap040921.html
http://antwrp.gsfc.nasa.gov/apod/ap961212.html

where is our milky way kid going
http://hypertextbook.com/facts/1999/PatriciaKong.shtml

[Lee Bruner]

http://antwrp.gsfc.nasa.gov/apod/ap040309.html

The ultra deep field. I find myself returning to look at this saved image often. To quote a Vulcan, space is really big.

[harry]

Hello Lee

Re link

http://antwrp.gsfc.nasa.gov/apod/ap040309.html

quote "What did the first galaxies look like? To help answer this question, the Hubble Space Telescope has just finished taking the Hubble Ultra Deep Field (HUDF), the deepest image of the universe ever taken in visible light. Pictured above, the HUDF shows a sampling of the oldest galaxies ever seen, galaxies that formed just after the dark ages, 13 billion years ago, when the universe was only 5 percent of its present age"

There is nothing wrong with the image only the silly statement made above.
It firstly assumes that the Big Bang is true and not a theory in the way that it says " first galaxies" and "5% of its present age"

Smile the galaxies seen in the image are similar to the galaxies that we see close to us in varies stages and forms it would have taken billions of years for them to form and not within the 5% age.

I sometimes wander who writes these articals.

[orin stepanek]

I agree Harry. The deep space galaxies ought to look different; but these look the same as the nearby ones.
Orin

[harry]

Hello Orin


Most of the apod images refer to the Expansion of the universe and the Big Bang. I still do not understand why.

[astroton]

Harry,

The progress of astrophysical theories have shown time and again that one behaviour could be explained in more than one way. Example is gravity.

The ultimate theory - the theory of origins - such as BBT obviously has a political bias. In this scenario the evidence will somehow be explained to support the most popular theory or let's say most powerful theory (The one supported by the power structure within the field).

The absolute truth will never be known and many such theories will, from time to time, take center stage. Those who oppose it will be dubbed negative or not in tune with science.

Result of human nature. History has shown that the theories of unknowns are written for the convenience of set audiences.

[orin stepanek]

Hi Harry! I think Astroton explains the 'why' pretty good; whether we believe that or not. Meanwhile I'd like to add this one to the favorites.
http://antwrp.gsfc.nasa.gov/apod/ap060421.html
Kind of reminds me of a giant amoeba; almost like it's alive.
Orin

[harry]

Hello Astroton.

I know and understand,,,,,,,,,,,,when I ask why I'm talking out aloud.

You would think in this day an age we would be more civilized. If people just agree with my ideas we could all go home. Smile,,,,,,,,,,,just joking.

Love it when people disagree. Adds wood to the fire.

Hello Orin
Loved your link http://antwrp.gsfc.nasa.gov/apod/ap060421.html
small image
http://ccd.cosmotography.com/images/small_ngc253.html
large image
http://ccd.cosmotography.com/images/lrg_ngc253.html

quote:
"In addition to its spiral dust lanes, striking tendrils of dust seem to be rising from the galactic disk in this gorgeous view"

these tendrils are quite interesting, they go for thousands of light years.

The question is what is causing these to occur at the same time. Could these be activated by Black Hole randomly distributed.

I have to build my space ship and go where no man has gone before me.

ooops or woman.
---------------------------------------------------------------------------
http://www.arxiv.org/PS_cache/astro-ph/ ... 509430.pdf
The answer is in this link.
tried to copy unable.

[astroton]

Orin and Harry,

My theory on Harry's Why was also a theory of unknown and as youcan see even that can be challenged, Oh God!

Harry,

It's difficult to not bring God into discussion.