[X] My Assistant

[David]

I'm looking at two animations of the asteroid 4 Vesta: the first is a sequence of images from the HST; the second several seconds of one HST image followed by a partial rotation of a shape model.

Why do I get the impression that these two animations are depicting different objects? I admit that much less of the rotation is shown in the shape model animation, which may lie behind the differences in impression, but that itself seems to me to be a problem. The shape model looks like a smooth oblate spheroid, with some distortion at the bottom (south?) pole, whose shape doesn't vary very much as it rotates. The HST sequence shows some pretty drastic changes in Vesta's profile as it rotates, including what must be a huge off-center crater in the upper (northern?) hemisphere, while the shape of the lower hemisphere is not nearly as flat as the shape model suggests. And yet one meets with quite a lot of references to Vesta being a "spheroid", which is hardly the impression I get from the HST rotation sequence. What gives?

[Phil Stooke]

The first animation is from quite early images, inferior in resolution. The attempt to deconvolve those images to reveal small details better (sharpening) has distorted the outline. In short it can't really be trusted. The second is based on higher resolution images. The shape model is by Peter Thomas of Cornell. A fictitious texture has been mapped over the shape.

Phil

[David]

The first animation is from quite early images, inferior in resolution. The attempt to deconvolve those images to reveal small details better (sharpening) has distorted the outline. In short it can't really be trusted. The second is based on higher resolution images. The shape model is by Peter Thomas of Cornell. A fictitious texture has been mapped over the shape.

Thanks! Is there a full rotation sequence of higher-resolution images?

[Phil Stooke]

Try this:

http://www2.keck.hawaii.edu/ao/Vesta2.html

Phil

[ljk4-1]

AstroAlert: Lunar Occ'n of Vesta, May 31, China, Japan, Korea; others in rest of 2006

==================================================================
This Is SKY & TELESCOPE's AstroAlert for Occultations
==================================================================

There are several lunar occultations of bright minor planets,
and of Uranus, this year that have not been widely publicized, and
some observations may have been lost. This tries to remedy that
problem, noting a very good lunar occultation of Vesta visible from
Japan, Korea, and China on May 31 at about 12h UT, as well as other
events visible later in the year from North America and other
locations around the world.

Although as early as October, Sky and Telescope sent me their
edited text for my 2006 Lunar Occultation Highlights article, I
probably noted at the time their mention of only the lunar
occultations of the brightest major planets, but in the rush of many
other things I did not notice when the January issue was actually
distributed in late November that my table of the lunar occultations
of the fainter planets was not included, and I only realized that
recently. Unfortunately, it's too late for the March 25th lunar
occultation of Ceres by a thin crescent Moon that occurred in
central North America, one of our better events of that type in that
area in several years. But it occurred shortly before the March
29th total solar eclipse and the April 1/2 lunar Pleiades passage,
so I think that everyone who might have been interested in that
event was already distracted by the other spectacles. We do have
another chance in the area with Iris on Dec. 3rd, but with a nearly
full Moon, it won't be as favorable as the March event. At least
the lunar occultations of Uranus are in Guy Ottewell's Astronomical
Calendar for 2006.

Below is the text and table that I prepared for the 2006
Highlight article; the table and the paragraph about lunar
occultations of minor planets was not published. They now are on
IOTA's main Web site at

http://www.lunar-occultations.com/iota

or directly at

http://www.lunar-occultations.com/iota/2006planetsbymoon.htm .

Rob Robinson can add more information there, such as area of
visibility maps and prediction lists; for specific events, ask him
about that by e-mail to webmaster@lunar-occultations.com . He can
also provide local predictions if you can supply your coordinates.
_____________

Planets. Three bright major planets will be occulted in 2006, as
well as Uranus and several relatively bright asteroids. There is
probably little new that can be learned from occultations of major
planets events in this age of space exploration, but they are still
interesting to watch.

2006 has an unusually large number of observable lunar occultations
of the brighter minor planets. Photometric records, possibly derived
from video recordings, could be used to determine the sizes of these
asteroids, although timings of occultations of stars by minor
planets give more accurate information.

Occultations of Planets, 2006
Moon
Date UT Planet Mag. Diam. Pl.% % Visible Area

Jan. 26 16h Amphitrite 11.4 0.08" 100 11- SW Pacific (Fiji)
Feb. 23 20h Amphitrite 11.4 0.09" 100 23- n.w. Australia
Mar. 25 11h Ceres 9.2 0.35" 100 21- central N. America
Apr. 24 14h Venus -3.7 18.6" 63 14- s. & e. S. America
May 31 12h Vesta 8.2 0.20" 100 19+ China, Korea, Japan
June 17 16h Uranus 5.8 3.5" 100 60- Antarctica, New Zealand
June 28 21h Vesta 8.2 0.19" 100 10+ n.e. Brazil
July 14 21h Uranus 5.8 3.6" 100 81- s. S. Afica, Indian Oc.
July 27 18h Mars 2.0 3.8" 98 6+ Europe, n.w. Africa
Aug. 11 6h Uranus 5.7 3.7" 100 95- s. & e. S. America
Oct. 2 12h Hebe 9.0 0.18" 100 72+ n. India, central Asia
Oct. 5 0h Uranus 5.7 3.6" 100 93+ s. S. America, Africa
Nov. 1 7h Uranus 5.7 3.6" 100 77+ s. Australia, NZ, Fiji
Nov. 28 16h Uranus 5.8 3.5" 100 54+ southeastern Asia
Dec. 3 8h Iris 7.2 0.31" 100 96+ n. & e. N. America
Dec. 10 11h Saturn 0.6 18.9" 100 70- Greenland, n.w. Europe
Dec. 25 22h Uranus 5.9 3.4" 100 31+ n.w. Africa, w. Iberia

David Dunham, IOTA