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Old 26-05-2013, 07:42 PM
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Blue Skies (Jacquie)
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Observing Occultations Using Video: A Beginner's Guide

Hi all,

After several years work I am pleased to announce that the first edition of the manual for recording occultations on video, titled "Observing Occultations Using Video: A Beginner's Guide", has finally gone live. Written under the banner of the Royal Astronomical Society of New Zealand's Occultation Section you can download a copy for your use at section's website at www.occultations.org.nz The website has recently shifted to a new host so if you haven't visited it in the last two weeks you will need to update your bookmarks.

I am currently in Invercargill, NZ, for the 7th Trans Tasman Symposium on Occultations (TTSO7) where we will have a discussion and feedback session on the document. Initial feedback from both experienced and inexperienced observers has been positive and I hope have a revised version out before the end of the year, or at least before NACAA 2014 next Easter.

In the meantime I invite you to have a read of the document and consider giving occultation work a go. It's far more than just trying to determine the shape of an asteroid these days; other contributions to the world body of knowledge include helping to refine asteroid orbits, refining the positions of stars, studying the atmospheres of planetary bodies to discovering and measuring the position angles of close binary stars via lunar occultations. Occultation work is also playing a major role in the New Horizons mission to Pluto, both in monitoring the current state of Pluto's atmospere and refining its orbit, which surprisingly is still not known exactly - at least not exact enough to precisely fly a space probe past it.
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Old 27-05-2013, 10:42 AM
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Good to hear from the "occultation community" in the science forum!

You are absolutely right, occultations have a broad application to many interesting problems, something I wish I would have realized when I was a foolish young man and used to make jokes such as the one about having sheep for companions during a grazing occultation.

cheers,
Robert
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Old 27-05-2013, 11:08 AM
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AstralTraveller (David)
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Thanks for this Jacqui and perhaps this will rekindle my interest in occultations. I was involved in some of the first grazing occultation in Australia back in 1976 and for a few years there was quite active but my interest has waned over the years, though I have organised a couple of graze trips in the last decade. Sheep for companions? Lucky you. At least it wasn't hoons, the police or shotgun-carrying locals.
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Old 27-05-2013, 02:53 PM
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Blue Skies (Jacquie)
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Thanks, David, your response is exactly what I was hoping to see. It would be nice to see a few more occultationists across the country. The feedback from the more experienced observers has been that they've still learnt something new and I hope it will bring them together towards a similar standard of quality.

Ah, the fun of grazes! I think everyone who has ever participated in one has at least one crazy story! That might be my next project, to collate a collection of graze stories.
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Old 27-05-2013, 08:59 PM
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A Very Famous Occultation; 3C 273 (in 1962)

Here is the story of one of the most famous occultations in history, that of the quasar called 3C 273 , in 1962.

At the time, the objects we now call Quasars were thought by many to be a sort of radio-emitting star with a very peculiar spectrum observed in the optical observations.

Astronomers had already shown that a subset of the powerful radio sources in the 3C catalog corresponded to these stellar-like objects seen in optical observations. However, at the time, the spectra of these objects - as observed in the optical domain - did not seem to make any sense at all!

Using the Parkes radio telescope, Cyril Hazard and his coworkers timed when the powerful 'stellar-like' radio source 3C 273 disappeared behind the moon, and again as it reappeared.
(they actually observed several occultations of 3C 273 in 1962)

They used these timings to obtain an accurate position for 3C 273 that could then be used by optical astronomers so that they could point their optical telescopes at it and thereby figure out "what the object is".

Using the occultation technique, Hazard & Mackey & Shimmins obtained a positional accuracy of better than 0.1 arcsecond for the radio source 3C 273, which at the time was the most accurate positional determination ever made for a celestial object.

With this position in hand, Maarten Schmidt, the other hero of this story, obtained an optical spectrum of 3C 273 with the 200 inch telescope at Mt Palomar.

To his eternal credit, Schmidt realized that the spectrum of 3C 273 was not some weird and inexplicable thing; he came to understand that it was a spectrum that was simply shifted towards the red a long way, indicating that 3C 273 was not just some bizarre star in our own galaxy.....
his interpretation that its high redshift implies that 3C 273 is billions of light years away, has held up to this day.

Here is the full story of this remarkable piece of detective work:

http://www.parkes.atnf.csiro.au/people/sar049/3C273
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Old 28-05-2013, 07:41 PM
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Quasars almost derailed Big Bang theory

Sorry for the off topic subject but Robert's post has an interesting side story.
In the early history of quasar observations and measurements, the redshift Z of quasars was found to cluster around two regions 0<Z<0.5 and 1.95<Z<2.2.

In Big Bang cosmology space time is expanding or rather the scale of space time is increasing and quasars are in fixed positions in space-time.
(The quasars are being "carried" by space-time rather than "moving through" space-time.)
The quasar distances from the observer are assumed to be random, hence the values Z should also be randomly distributed due to Hubble's Law.

This apparent non randomness led some cosmologists to seriously consider that redshift was not a reliable measure of distance with serious consequences to the Big Bang model.
This lead to some pretty bizarre non expanding cosmological models being developed such as one based on Godel's metric which was a non expanding rotating Universe.
(Incidentally Steady State Universe models are expanding models, the term steady refers to the density of the Universe being constant. In the BIg Bang model density decreases with time.)

With more quasars being identified and measured the clustering became less obvious.
Even today however some Cosmologists such as Narlikar see some sort of pattern in the Z values.
This has been rejected by mainstream as an example of selection bias in the sampling data.

Regards

Steven

Last edited by sjastro; 29-05-2013 at 09:39 AM. Reason: spelling
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Old 28-05-2013, 08:20 PM
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Quote:
Originally Posted by sjastro View Post
Sorry for the off topic subject but Robert's post has an interesting side story.
In the early history of quasar observations and measurements, the redshift Z of quasars was found to cluster around two regions 0<Z<0.5 and 1.95<Z<2.2.
I recall some papers by someone called W.G. Tifft, which were actually accepted for publication in some respected high-impact journals, that claimed that redshifts have some kind of characteristic separation or periodicity ("quantized redshifts")
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Old 28-05-2013, 08:49 PM
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Quote:
Originally Posted by madbadgalaxyman View Post
I recall some papers by someone called W.G. Tifft, which were actually accepted for publication in some respected high-impact journals, that claimed that redshifts have some kind of characteristic separation or periodicity ("quantized redshifts")
Hello Robert

The "quantized redshifts" are the patterns that have supposedly been observed in galaxy and quasar data.
These have been rejected as selection effects.

Regards

Steven
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