In article , (Steve Willner) writes:
In article ,
(Paul Schlyter) writes:
It would definitely be too small to observe in transit: the apparent
diameter of this body, when it's closest to the Earth, is expected to
be between 0.03 and 0.06 arc seconds.

Are you sure that's too small? What's the angular resolution of
solar telescopes these days? Observing a transit doesn't require
resolving the asteroid disk, only detecting the brightness decrease
it causes. That depends on signal to noise, which is probably
limited by variations in the solar surface brightness. I don't know
the numbers, but it isn't obvious to me that the observation is
impossible.


Currently, solar telescopes using state of the art adaptive optics systems
are achieving resolutions on the order of 0.15 arc seconds over relatively
small fields of view. The solar telescopes producing the best images have
effective diameters of about 1 meter. The proposed Advanced Technology
Solar Telescope (ATST) is a 4 meter class telescope designed to have a
resolution of 0.03 arc seconds at 550 nm.

The contrast of the granular structures on the Sun is a few percent. Many
solar observations are photon limited and signal to noise suffers from a
lack of photons. This is due to a lot of our observations are taken at
very high spectral resolution (spectrographs having a spectral resolution of
delta lambda/lambda 1,000,000 are not uncommon and imaging systems having
a spectral resolution of delta lambda/lambda on the order of 250,000 exist).
An additional complication is that we also desire very short exposure times
(a few milliseconds) to reduce image blur due to seeing and to properly
sample the changes with time of solar structure.

Even if a transit is observable, I'm not sure what its scientific
value would be. Presumably it would determine the asteroid diameter,
but is there much value in that? On the other hand, if a solar
telescope is observing the Sun anyway, you get the transit
observation "for free," so why not make use of it?


Transits and eclipses are useful to measure scattered light in our optical
systems. In any case, I don't think a transit of a body 0.06 arc seconds
in diameter could be seen anytime in the foreseeable future.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)



__________________________________________________ ______________________
Craig A. Gullixson
Instrument Engineer INTERNET:
National Solar Observatory/Sac. Peak PHONE: (505) 434-7065
Sunspot, NM 88349 USA FAX: (505) 434-7029