Dear NASA and ESA: Thanks for Cassini-Huygens

Seeing Saturn as a child through a reasonably good amateur telescope was one of many formative experiences in my life. When the planetary 'seeing' was good (a still atmosphere is more important than how dark or clear the skies are when looking at anything in the solar system) and Saturn was well above the horizon, a 6 inch f8 Newtonian reflector showed the three main rings, some detail in the atmosphere, and as many as half a dozen moons. Though, really, the moons were just Titan and assorted specks.

Then, for the last 20 years, we've had Cassini-Huygens. Here's a composite image of Saturn eclipsing the Sun. It's one of my favorites, and definitely worth a click.

All day today NASA TV will be rerunning Casssini programming. At 7 a.m., Friday, September 15 (that is Eastern daylight, UTC -0400) they start End of Mission Commentary, etc. There will be new content appearing for a while, then they'll start rerunning it. The schedule is at https://www.nasa.gov/multimedia/nasatv/schedule.html.

It's amazing how much we're learned about the Saturn system my childhood days. There's a good summary of what NASA judges to be the Top 10 at https://saturn.jpl.nasa.gov/news/2892/cassini-10-years-at-saturn-top-10-discoveries/. Be sure to look at some of the links below the subsections. For instance, under #7 'Vertical structures in the rings imaged for the first time', there's a link to https://saturn.jpl.nasa.gov/news/2442/cassini-reveals-new-ring-quirks-shadows-during-saturn-equinox/. From that link,

The chunks of ice that make up the main rings spread out 140,000 kilometers (85,000 miles) from the center of Saturn, but they had been thought to be only around 10 meters (30 feet) thick in the main rings, known as A, B, C, and D. 

140E6 meters in diameter to 10 meters in thickness, or 14E7 to 1. That is a remarkable ratio. To look at 14 million to 1 on a more human scale, pack that ring diameter into the distance from Los Angeles to New York City, which is 3940 km or 2448 miles, as the crow flies. That gives us a reduction of 140,000 / 3940, a factor of about 35.5. Our thickness then becomes 10 / 35.5, or about .281 m, or 281 mm, or 11 inches. That seems pretty thin!

If it's the best data available, I would imagine a lot of people spent time arguing about the physics of how such a structure might have evolved and survived. But then came Cassini-Huygens, and an explosion of new knowledge about a dynamical system. From that same page,

In the new images, particles seemed to pile up in vertical formations in each of the rings. Rippling corrugations -- previously seen by Cassini to extend approximately 804 kilometers (500 miles) in the innermost D ring -- appear to undulate out to a total of 17,000 kilometers (11,000 miles) through the neighboring C ring to the B ring.

The heights of some of the newly discovered bumps are comparable to the elevations of the Rocky Mountains. One ridge of icy ring particles, whipped up by the gravitational pull of Saturn's moon Daphnis as it travels through the plane of the rings, looms as high as about 4 kilometers (2.5 miles). It is the tallest vertical wall seen within the rings. 

It seems likely to provide important clues to our understanding proto-planetary disks.  Exploring those links will be time well spent. Unfortunately for me, lunch is now over. But the yield from Cassini-Huygens is very far from over; these data are going to be the basis for important research results for decades. I look forward to it being an enormous time-sink over the coming years. More immediately, I'm going to catch some of that NASA TV coverage tomorrow, cup of coffee in hand. Because it will be 0400 here on the West coast, at the start of what's going to be a busy day.

You Can Never Get Enough Corona Time

1m11.4s was the duration, of which I missed the first second or so looking for, and failing to spot,  shadow bands.

But wow, did I get a great binocular look at prominences. After it was over, I caught a broadcast from Nebraska  at https://www.nasa.gov/eclipselive/#NASA+TV+Public+Channel. I was fortunate enough to see far more than were seen there. That pure pink Hydrogen-alpha light is beautiful. Pure like laser light, but without that speckled quality. And I did see a great Diamond Ring at the end of totality.

The 1979 eclipse was better, overall. Longer, and I saw it from a location with long views, and fantastic shadow bands. This time, no bands, and without long views from a high point, I didn't see the moon's shadow racing across the ground. That provides the visual cue that allows you to realize that you are seeing the clockwork' of the solar system. Maybe west Texas in 2024?

OTOH, no racing around trying to find a blue hole to see it through: it was nice and clear. No worries about forest fire smoke, and all I had to do was walk outside and have a seat. If you are ever given a choice of locations, pick the one that overlooks surrounding terrain. It was just unfortunate that I didn't have that opportunity this time.

That said, this is is very far from anything like an expression of disappointment. It was awesome --  a word I don't use casually. I had forgotten about that rapid decrease in light during the last minute or so before totality. Very dramatic, and having forgotten about it, it was pretty much a New Thing for me.

People were parked all over the roadsides, a parking lot at a nearby boat launch was beyond normal capacity, and I could hear the cheering when the corona jumped out from my place, half a mile away. Obviously some very happy people.

What a wonderful morning.

Solar Eclipse Timing for Peoria, Oregon

Eclipse timing for Peoria, Oregon, but times and alt/az will be close for Corvallis, Albany, Shedd, etc. I was just outside planning how I was going to lay out a white surface to try to photograph any shadow bands that might appear. Thought this might be of interest, so I did a quick cut-n-paste from a text file.

Touches down on the Oregon coast between Lincoln City and Newport at 10:15 a.m. PDT.
Following data from:
https://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html
I added the PDT (-7) times.
Lat.: 44.4[redacted]° N
Long.: 123.2[redacted]9° W
Total Solar Eclipse
Duration of Totality: 1m11.4s
Magnitude: 1.003
Obscuration: 100.00%
Event                         Date        Time (UT) PDT       Alt Azi
Start of partial eclipse (C1)  2017/08/21 16:04:50.  09:04:50  6 27.6° 100.8°
Start of total eclipse (C2) :   2017/08/21 17:17:10.  10:17:10  3 39.9° 116.3°
Maximum eclipse :       2017/08/21 17:17:45.  10:17:45  9 40.0° 116.5°
End of total eclipse (C3) :     2017/08/21 17:18:21.  10:18:21  7 40.0° 116.6°
End of partial eclipse (C4) :  2017/08/21 18:37:29.  11:37:29  7 51.2° 139.5°

Crab Nebula with 5 telescopes

The composite is linked above above, from this starting point for all this here on hubblesite.org. There are links to the individual images from the five telescopes involved, covering five spectral regions. Highly recommended.

• Very Large Array (radio)
• Spitzer Space Telescope (infrared)
• Hubble Space Telescope (visual)
• XMM-Newton (ultraviolet)
• Chandra X-ray Observatory (X-ray)

It turns out that there were almost six telescopes involved. Pulling from the science paper (Drubner et. al.):

"We have also used the Atacama Large Millimeter/submillimeter Array (ALMA) to produce the first detailed radio continuum image of the center of the nebula at 100 GHz, although the ALMA observations were not contemporaneous with the others ..."

The features near the center of the nebula were moving at ~ 20% light-speed, and over ~6 months of observations of a  supernova remnant that is 'only' 6500 light years away, had moved ~2 seconds of arc. Which led to a corrupted image.

Too bad, but of course there is a lot going on in the immediate vicinity of a pulsar.

Before leaving that page, I have to point out this short linked video https://media.stsci.edu/uploads/video_file/video_attachment/4408/STScI-H-v1721a-1280x720.mp4. It morphs the images through the spectrum, and it's annotated by spectral band. There's also a version without the annotations.

If you'd like to see changes in the Crab Nebula, similar to what I mentioned mentioned, here you go. This is from Chandra as well, but the page won't load. So here it is on YouTube. Seven months of changes, very near the pulsar, in a few seconds.

So, what else goes on in a nearby supernova remnant?

A lot. As one might expect, there is a lot of very energetic physics packed into a small area, only 6500 light-years away. When the supernova which left the Crab Nebula behind was recorded by Chinese, Japanese, and middle eastern astronomers in 1054, it would have been easily brighter than any star or planet in the sky. 

What began as a star on the order of 10 times the mass of the sun, left a neutron star only about 20 miles across, but weighing ~4.5 billion pounds per cubic inch. It's rotating 30 times per second, because angular momentum was conserved during the explosion. The energy it radiates doesn't stop in the X-ray regime that was observed by Chandra, but extends all the way up to ~10 TeV. That is similar to the LHC, whose initial energy was 7 TeV, but is now running at 13 TeV, but at a vastly higher power level. The LHC beam, after all, is about the diameter of a sewing needle.

The magnetic fields involved are enormous. That doesn't happen due to a conservation law, as in rotation; in fact exact mechanism is still unclear.  What is clear is that their reach is large. Here's an image from NASA's Hubble Captures the Beating Heart of the Crab Nebula (recommended). That pearly blue glow is synchrotron radiation, produced by electrons spiraling in a magnetic field.

Everything near a pulsar that can be ionized is ionized due to those high-energy emissions. What's left are carbon and silicate dusts, and even those seem likely to be mostly charged, though electrostatically). So we have positively charged ions, and those now-free electrons. Those free electrons are pervasive, hence the blue glow.

That ionization, the pulsars intense gravitational and magnetic field, and rotation combine to give rise to those famous pulses that gave pulsars their name. The basic mechanism is 

1. some of the material ejected in the supernova is pulled back into the star
2. the in-fall is caught in the magnetic fields, and pulled toward the poles
3. it's beamed back out at the poles, rather like lighthouse beams
4. the beam sweeps across us, in this case 30 times per second

4. is possible because the axis of rotation is not aligned with that of the magnetic field. That seems a bit counter-intuitive, but it's also the case with the sun, and even here on earth (and something that has to be considered when navigating by compass). That's too much to go into here; books have been written about the Crab. Search on 'dynamo effect' or 'dynamo theory'.

We have been learning about this for a millennium now. While the pace of discovery is accelerating, the story of the Crab Nebula is far from told.

Total Solar Eclipse 2017

I live in a pretty cool place, from a certain nerdy viewpoint. 119 species of birds, two years running, might indicate a certain predictability, but a closer look at the data destroys that notion.

So how cool is this place, really? My subjective measures include things like species counts, whether I can get reasonable photos, etc. Subjective in this case means entirely subjective. So what might tip this place into Coolest Place I Have Ever Lived?

Yeah, that might do it. Though no photo did it justice. Film doesn't have the dynamic range, and digital cameras are worse in that respect. There's a wide pearlescant glow from the solar corona seen IRL which is entirely missing from short exposure times. This image predates optimizing over a set of stacked images.

It's a photo of a photo that has been hanging on some wall of pretty much every place I have ever lived since 1979. Yes, I am an old fart: deal with it. No, it's not related to Sauron in any way, save perhaps as being inspirational to film-makers for major production houses. Possibly. The mechanics of of how films are actually made (and taxes, payments to the Tolkien estate avoided, etc.) entirely escape me.

You may want to visit https://en.wikipedia.org/w/index.php?title=Solar_eclipse_of_February_26,_1979&oldid=761573206

That's the link as of this date: I've been burned by not specifying specifying dates. Pull quote:

Many visitors traveled to the Pacific Northwest to view the eclipse,^[1] since it would be the last chance to view a total solar eclipse in the United States for almost four decades. The next over the United States will be the total solar eclipse of August 21, 2017.
Although the path of totality passed through Portland, Oregon in early morning, it was not directly observable from the Portland area due to overcast skies.^[2]

That last line matters. In 1979 I was driving up the Columbia Gorge, seeing small holes of blue sky in wide overcast, and trying to judge where said blue holes might line up with the sun, during that brief period of totality. A fast car and a certain disrespect for law and order won the day. Everything lined up, and I skidded to a stop at Horsethief Lake State Park in time to see the whole event.

• Shadow racing through the gorge at a thousand miles per hour
• Weird greenish light, entirely unexpected, before totality
• Shadow bands rippling across the ground.

It was awesome, in the original sense of the word. This is the Pacific NW. I saw Mount St. Helens erupt a year later, so I'm not a stranger to drama.

So here we are, that long 40 years later, as mentioned in the above pull quote. I'm now a certifiable Old Fart who never expected to live this long. But that narrow path of totality will sweep directly over my place  on August 21. In place of vile winter weather,  I have the best weather of the year, and all I have to do, essentially, is walk outside. How cool is that?

Being a complete nerd, I'll go bit further. I'll spread my parachute canopy across the yard below a second-story deck, and hope for a shadow band photo opportunity, etc. But mostly, I just want to experience the event. I lack the words to describe a total solar eclipse. Perhaps that is the true meaning of 'awesome': you just can't really express it.

Of one thing I am certain: on 2017-08-21, this weird little place in small-town Oregon will become The Coolest Place That I Have Ever Lived.