CHANDRA AND FULTON STREET
-----------------------
John Pazmino
NYSkies Astronomy Inc
nyskies@nyskies.org
www.nyskies.org
2006 November 12 initial
2020 July 31 current
[This article was recovered in July 2020 in AN incomplete state. Altho
the missing sections are lost, there are enough in this piece to
summarize the AAVSO 2006 annual meeting. The header had ediurnate
contacts, updated here. ] previously put into the NYSkies web the
abstract for my talk at the meeting, copied from the AAVSO Journal,
This remains in the NYSkies web titled 'sunshine at ground zero'. I
inserted it into this instant piece, with some recollection of my
talk.
Introduction
----------
The 95th annual autumn meeting of American Association of Variable
Star Observers convened in Newton, Massachusetts, on 26-28 October
2006. The sessions were held at the Sheraton Newton, the same hotel as
for last year's fall meeting. This year's convention included an open
house supper at AAVSO headquarters, a workshop for the Chandra X-ray
Observatory, and a keynote speaker about Hubble and Webb space
telescopes.
I represented New York City astronomy thru NYSkies and, because of
timeliness, Allies in Space. I brought take-ones for assorted
litterature about both, plus an extra goodie, explained below.
To and from Newton
-----------------
It has been for some many years all around best to travel to the
AAVSO fall meetings by train. For meetings in or near Boston, I ride
the whole route from Penn Station to Boston South Station. In the case
of the two conventions in Newton, for 2005 and now 2006, I got off at
Route 128, two stops before South Station. In 2005 I did so due to
extraordinary nasty rain, making it humanly impractical to got to
South Station and take a city bus back to Newton. I got off at Route
128 to get a taxi for what I figured was a much shorter ride than if I
got one from downtown Boston.
For this 2006 meeting the weather was mild and sunny. I exited at
Route 128 for the convenience of the taxi ride. Unlike in 2005, the
taxi took me to the proper hotel in one go with no silly surprises.
Going home from the Sheraton hotel, the taxi driver explained that
Back Bay station was closer and cheaper than Route 128. He took me
there to meet my train for a fare roughly 1/2 that to Route 128. The
weather was still sunny and mild, but now windy with gusts.
The Sheraton hotel
----------------
I described this hotel in the report for the autumn 2005 meeting.
There were no substantial changes in services or facilities. The
significant difference was that with the pleasant weather, we were
able to wander around the surrounding streets, not be cooped up within
the building by massive rainfall.
One glitch affected several delegates, including me. The hotel
asserted that the convention rate, $98/night, applied for only Friday
and Saturday night, not for Thursday. If we stayed for Thursday night,
we would pay the rack rate of $199/night.
I and the others protested that the convention starts on Friday
morning, requiring us to be on site for Thursday night. I even got a
partial bill for that first night with the regular charge on it! AAVSO
crew spoke with the management to apply the convention rate to all
three nights for all delegates. One argument supporting this was that
the reduced rate was given to AAVSO crew who had to stay on Wednesday
night to set up for the convention.
For me there was an other glitch. I took supper in the hotel's
restaurant on Thursday night and put the charge on my room. It was
missed off of the final bill when I checked out on Sunday morning. I
called attention to this omission, which was promptly verified and
restored to the bill.
Hometown poster
-------------
In recent years, since the episode in Hawaii, where my hometown
poster was confiscated for showing the late World Trade center, I use
prints of my presentation as the poster on my room door. My talk at
AAVSO was 'Sunshine at Ground Zero?'. I had maps, diagrams, photos of
the landscape around Ground Zero.
These were well appreciated by delegates in rooms near mine. Many
recalled the fall of the Twin Towers in some personal way, making for
lively small talk. One diagram was am old map of Lower Manhattan to
show the street pattern removed for the future World Trade Center. Of
the many early maps I found on websites, I picked a particular one
from 1918 for its detail and many curious other features. It was so
nice that I printed a bunch as take-ones for the litterature table.
They went quickly.
At first, the delegates were puzzled; what does this have to do
with astronomy? It wasn't until they heard my talk that they
understood its significance. Those from the New York area were
delighted to explore the map, many features of which were familiar to
them in former years.
Chandra X-ray Observatory
-----------------------
Friday the 27th was an all-day workshop about the Chandra X-ray
Observatory. The session offered an overview of the satellite,
education demonstrations, and tuition on data processing. It also
emphasized the crucial part home astronomers play in correlating
observations by Chandra with those in the optical band.
Chandra X-ray Observatory is the third of NASA's Great Observatory
series of astronomy satellites. The first two were Compton Gamma-ray
Observatory and Hubble Space Telescope. The fourth and last is Spitzer
Infrared Observatory. Compton ended its service several years ago. The
other three are still running.
The satellite was originally the AXAF mission. It was renamed tin
part to honor Chandrasekar, mid 20th century pioneer in high-energy
astrophysics.
Chandra was launched in July 1999 from Shuttle Columbia on flight
STS-93. Chandra is a one-shot mission with no provision for in-orbit
repair or upgrade. It was commissioned for full service in September
1999. It orbits in a 140,000 x 10,000 kilometer ellipse to get it
outside the Earth's radiation belts.
It is a substantial craft of 20 meter width across the solar
panels, 12 meter length, and 4.8 ton mass. It sports several cameras
and spectrometers and can capture data every 3 seconds at 0.5 srcsec
resolution.
Chandra operations
----------------
The ground station for Chandra is at the Harvard-Smithsonian
Center for Astrophysics at Harvard University, Cambridge MA. The
office is walking distance of AAVSO but so far there was no formal
visit to the facility during an AAVSO convention.
Chandra has an extensive education and public information
operation, which included this very workshop. However, unlike Hubble,
Chandra is virtually unknown by lay people. Hubble does have a
overwhelmingly higher public profile from past and possible future
human visits via the Space Shuttle. Chandra, typical of satellites, is
a one-shot project. When it breaks down, it's abandoned.
Home astronomy and Chandra
------------------------
Chandra, like other observatories in space working extraoptical
wavebands, often requires correlative observation in the optical
bands. SInce many targets vary over time in radiation output, it was
natural for AAVSO to include them in its own visual observing program.
Not all targets are 'stars', but may be supernova remanents, globular,
or planetary, nebulae, interacting binary stars, quasars, active
galaxies. The brighter specimina can be observed by eye at the
telescope.
AAVSO has long worked with space observatories to monitor their
targets. The two sets of record help develop theory of astrophysical
behavior of the target over the prime and optical part of the
spectrum. The AAVSO monitoring may be at stated times to coincide with
the satellite observing, or it may be before or after that time. The
choice depends on the target's peculiar behavior. Optical monitoring
may be a crash effort in response to unexpected activity in a target.
Wavebands and energy
------------------
I note here the even handed way we astronomers treat radiation as
energy or particle. We may bring out the wave or particle character as
we want by suitably constructing our instruments that detect them. It
turns out that for the most part, as the wavelength is shorter, the
particle nature of the radiation is easier to show. Longer wavelengths
tend to be treated as a flux of energy as waves.
The X-ray spectrum can be specified by either mode, according as
the background of the astronomer and the instruments he works with.
We may see the X-rays nearer to ultraviolet stated in wavelength or
frequency. Those nearer to gamma-rays are stated in energy.
The two methods are equivalent by the photon model. Radiation is
packaged in quanta, tiniest 'particles' commonly called 'photons'. The
term comes from their initial use in optical photometry but being that
a photon of light is identical to that of any other electromagnetic
radiation, the concept is extended thruout the spectrum.
A photon, or quantum, has an energy content of
(energy) = (Planck constnt)*(lightspeed)/(wavelength)
= (Planck constnt)*(frequency)
= (Planck constant)*(lightspeed)/(wavelength)
The Planck constant here is the 'big' one, with the factor of 2*pi
folded into it. The 'small' Planck constant is also widely used and
you must be careful to tack on the 2*pi factor in the above formulae.
There is no prescribed preference for stating a photon. Go along
with the tradition in each section of the spectrum. You can commute a
one mode -- wavelength, frequency, energy -- onto any of the other two
as you want to.
Data collection
-------------
Chandra, and many other observatories, does not 'take pictures' in
the conventional sense. It collects information about the photons
energizing each pixel in the sensor matrix. These pixel parameters are
radioed to Earth and stored for later examination. The astronomer who
collected the data then assembles the pixel readings in what ever way
is appropriate for his project. It may be a 'picture' or a graph or a
tabulation or synthetic image. There is no 'original' to revert to
except the raw pixel data themselfs.
This concept of Chandra imaging is a bit tricky for many home
astronomers to deal with. They are so used to seeing, well, pictures
from regular observatories. They may themselfs take photographs or
CCDgrams and produce pictures.
Published pictures are only ONE interpretation of the collected
information and can not be treated as th 'true' representation of the
target.
Chandra, in the workshop examples, collected data every three
seconds over its full range of energy 0.1Kev thru 10Kev. In fact, the
astronomer may call for data only in certain energy bands, leaving out
the others. The data then lacks the left out energies. An other
astronomer who for his project examines the same target for other
purposes may select a different set of energies.
The data for Chandra is accumulated over many minutes, so they
contain complete sets of three-second snapshots of the sensor pixels.
The astronomer may select certain of these snapshots to compose into
his image. Thus, it is not possible to naively compare two
dissociated images just because they are of the same target.
Time content
----------
Think of a regular photograph of a star field of, say, one hour
duration with no tracking. You get star trails and maybe a meteor
streak and an artificial satellite line. Just from the picture you can
not tell which direction the three objects (stars, meteor, satellite)
are moving. You could guess from external reference, like the
constellation catch figure, that the stars move from right to left.
You could surmise from the changing shape and brightness of the meteor
that it moved top to bottom. The satellite trail is a lot trickier to
suss out. It could be moving lower-left to upper-right or vice versa.
Only for the stars can you know when their image was captured.
That's because, you already know the behavior of the stars. For the
meteor and satellite, you can not know from the internal information
of the picture, when they passed by.
Even for the stars, one of them could have flared up and register
a brighter dot. But when did this happen and how was the brightness
changing during the exposure? This information is missing.
The time element of the scene is lost by treating every photon the
same regardless of when it impinged on the film. All you know is that
they came sometime within the one hour that the shutter was open.
In the case of X-rays the changes in received radiation during the
exposure can be crucial for the project you're working on. X-ray
radiation can alter on timescales of seconds, based on prior
experience. Just seeing an enhanced spot on the hour-long ordinary
photograph tells you only that somehow there was more radiation there
then elsewhere in the picture.
Chandra's layering of data to compose a synthetic image allows for
time resolution, with accompanying deeper information about the
target. The astronomer can select 'slices' of the data snapshot by
snapshot. It's like taking a video of the sky for one hour, then
examining the individual frames. You now see the crescent flare of the
star and its decline. You see the meteor start near one corner and
migrate to the middle. You see the satellite enter from one side and
leave at the opposite side. To recreae the photographic image, you
stack the frames and do a composite shot thru all of them.
DS9 FITS processor
----------------
In order to manipulate Chandra data, the data are archived in FITS
format. This is a standard method of organizing astronomy imaging
information that captures all the internals of the collection process,
including the time content. To examine the FITS data, a FITS
processor, a super version of regular image processors, is needed.
You need more than a simple FITS viewer, a program that lets you see a
frozen single composition of FITS data.
As it turns out, such FITS processors were used for many decades
by campus astronomers running UNIX computers. Home astronomers almost
universally operate Windows computers. Linux, a home computer
implementation of UNIX just never caught on.
The Chandra ground base developed a whole new program called DS9,
from the Star Trek movies, that runs under Windows and mimics the UNIX
program's operations. The conversion is not complete in that it merely
translates Windows operations into the equivalent UNIX operations and
sends them by Internet link to the Chandra station. There the commands
are processed and the data returned to the home computer. Usually this
is a picture of some sort.
Altho the program can be distributed on disc, it is dead until the
Internet link is established. Due to the massive amount of data
transferred, a high-speed link is required, like DSL. A dial-up modem
link is way too slow.
The learning curve for DS9 is steep for home astronomers because
the operations are not the familiar ones found in regular image
processors. They all have some functions peculiar to astronomy, with
concepts sometimes beyond the home astronomer's experience.
What's more, the available functions are dynamicly tied to the
particular data source. DS9, altho built as part of the Chandra
educational services, can be applied to any other archive of FITS
astronomy data. As a particular data set is opened, certain of DS9's
menu items are shut off for being not valid for that dataset. You work
with just the ones activated.
Photons and energy
----------------
One topic that threw some of us was the distinction between the
number of photons on a given pixel and the accumulated energy with
them. The first is merely the count of quanta within a selected
waveband. The latter is the count multiplied by the energy of the
quantum of that waveband. Hence, if you wanted to filter the pixels to
display only if their energy exceded a given value, regardless of
waveband, you would get a very different result than one where the
count exceded a certain value, regardless of quantum energy. The
units of count are easy enough, counts/second. Those of energy are
erratic from dataset to dataset. They may be in watt/meter2.hertz or
any other permutation of this measure. That includes use of the CGS or
MKS or SI system and use of either frequency or wavelength. Unless you
are thoroly acquainted with physics from many disciplines, the units
in your instant situation may look awfully strange.
All in all, the demonstration was a bit challenging for some of us
to follow on the fly. It took some extensive Q&A and then banter in
the hallways to sort out everything. The main point to came away with
is that Chandra and the other observatories need and use and
congratulate the home astronomer contributions.
Sunshine at Ground Zero
---------------------
This is the AAVSO abstract, followed by me recollected notes.]
= = = = =
Sunshine at Ground Zero
-----------------------
'The site of the late World Trade Center in New York is under
development. The new World Trade Center, although itself a substantial
project, differs significantly from the late one. One feature is to
dedicate a section in the campus where the Sun shines during the
memorial hours, 08:46 through 10:29 EDST, on every September 11th.
This astronomy feature is the "Wedge of Light." But will it work? Is
there a true "wedge of light" at Ground Zero?'
= = = = =
My presentation at the meeting was 'Sunshine at Ground Zero',
explaining the concept of the proposed Wedge of Light on the campus.
The [;am is to leave a clear sightline to the morning sun on every
September 11, 08:46 tp 10:29 EDST. These are the moments when the
first airplane collided with the north tower and when the south tower
collapsed. The north tower fell and the second plane smashed into the
south tower between these moments.
The new WTC occupies the same land as the late WTC with the
extension of Fulton Street and Greenwich Street into it and the 9/11
memorial in the southwest corner. The prolonged streets breaks up the
campus into human-scale sectors.
The rest of the land is open for replacing floorage, one full
square kilometer!, equal to that of the late Twin Towers.
As part of the rebuilding, a single tower, Freedom Tower, will
stand at the northwest corner of the campus. It will be the tallest
office tower on Earth, about 540 meters high. Four other towers, 300
down to 200 meters tall, will stand on the east side of the campus.
It was a stroke of good luck that there actually is, in spite of
circumstant skyscrapers, an open sky exposure to the Sun . It shines
from over Brooklyn Bridge, past City Hall Park and St Paul's Chapel,
into the campus.
The plan situates the new WTC skyscrapers to avoid intrusion into
this sunlight corridor. The shadow of the farthest north skyscraper,
on the left as viewed from the extended Fulton Street, would slide
away before 08:46. The shadow of the next tower, on the right, would
slide over to block the Sun a little after 10:29. The sweep of
sunlight between the bounding shadows is the Wedge of Light.
There would also be no obstructions on the grounds, like lamp
poles, large artwork, trees, to let the Sun illuminate the full east-
west length of the campus, to the front of Freedom Tower. It will be
paced from St Paul's Chapel to Freedom Tower by walking along the
extended Fulton Street.
An other structure on the east flank is a new station house for
the Hudson Tubes, or PATH, train, which in the late WTC had no surface
entrance. Trains, seven seven floors below grade, were reached from
inside the late WTC buildings. Since 2001 the rail works were repaired
and reached by temporary entrnces on the campus.
This pavilion is designed by architect Calatrava as a porcupine
structure with new escalators to the train platforms. The roof is a
clamshell that opens up by massive hydraulic jacks to let sunlight
into the main hall between the hours of the September-11 catastrophe.
It will stay closed during precipitation.
A public flap erupted when the Calatrava design was released. All
of his other works wee planned for viewing from the ground or a couple
floors above. The PATH pavilion can be seen from surrounding towers,
such as those building for the WTC!. The spreading porcupine spokes
and slit in the open roof look too much like a woman's thighs and
crotch!
Conclusion
---------
This article, even with the patch for my presentation is deficient
in many facets of the AAVSO convention. It does cove many features to
hopefully offer a useful summary. The presentations were mature,
organized, thoro. The hallway and interlude chars enhance the talks,
often y face-to-face discussion with the speaker.
The workshop was particularly important for home astronomers who
interpret and explain space missions to junior club members and the
public. Radiation and quantum physics are not part of the usual
tuition for home astronomy