4,513 research outputs found
Comet Halley and history
A history of Halley's Comet is presented. Comets Kohoutek and Ikeya-Seki are discussed
Nongravitational forces on comets
Methods are presented and discussed for determining the effects of nongravitational forces on the orbits of comets. These methods are applied to short-period and long-period comets. Results are briefly described
Astrometric observations of comets and asteroids and subsequent orbital investigations
Comets and minor planets were observed with a 155 cm reflector. Their orbital positions are presented in tabular form
On the Size-Dependence of the Inclination Distribution of the Main Kuiper Belt
We present a new analysis of the currently available orbital elements for the
known Kuiper belt objects. In the non-resonant, main Kuiper belt we find a
statistically significant relationship between an object's absolute magnitude
(H) and its inclination (i). Objects with H~170 km for a 4%
albedo) have higher inclinations than those with H>6.5 (radii >~ 170 km). We
have shown that this relationship is not caused by any obvious observational
bias. We argue that the main Kuiper belt consists of the superposition of two
distinct distributions. One is dynamically hot with inclinations as large as
\~35 deg and absolute magnitudes as bright as 4.5; the other is dynamically
cold with i6.5. The dynamically cold population is most likely
dynamically primordial. We speculate on the potential causes of this
relationship.Comment: 14 pages, 6 postscript figure
The study of the physics of cometary nuclei
A semiannual progress report describing the work completed during the period 1 September 1975 to 29 February 1976 on the physics of cometary nuclei was given. The following items were discussed: (1) a paper entitled ""A speculation about comets and the earth'', (2) a chapter entitled"" The physics of comets'' for ""Reviews of Astronomy and Astrophysics'', (3) continuing work on split comets, and (4) results dealing with a new application of nongravitational solar-radial forces as a measure of comet nucleus dimensions and activity
Astrometric observations of comets and asteroids and subsequent orbital investigations
The transformation of the Oak Ridge astrometry from a photographic program to a charge coupled device (CCD) program can now be considered complete, and the number of observations being made is now approaching an order of magnitude greater than in the old photographic program. Astrometric observations with the 1.5-m reflector were made at the Oak Ridge Observatory, and the progress, accomplishments, and projected accomplishments are presented
Cometary Astrometry
Modern techniques for making cometary astrometric observations, reducing these observations, using accurate reference star catalogs, and computing precise orbits and ephemerides are discussed in detail and recommendations and suggestions are given in each area
Variational Principles for Lagrangian Averaged Fluid Dynamics
The Lagrangian average (LA) of the ideal fluid equations preserves their
transport structure. This transport structure is responsible for the Kelvin
circulation theorem of the LA flow and, hence, for its convection of potential
vorticity and its conservation of helicity.
Lagrangian averaging also preserves the Euler-Poincar\'e (EP) variational
framework that implies the LA fluid equations. This is expressed in the
Lagrangian-averaged Euler-Poincar\'e (LAEP) theorem proven here and illustrated
for the Lagrangian average Euler (LAE) equations.Comment: 23 pages, 3 figure
Orbit Fitting and Uncertainties for Kuiper Belt Objects
We present a procedure for determination of positions and orbital elements,
and associated uncertainties, of outer Solar System planets. The orbit-fitting
procedure is greatly streamlined compared to traditional methods because
acceleration can be treated as a perturbation to the inertial motion of the
body. These techniques are immediately applicable to Kuiper Belt Objects, for
which recovery observations are costly. Our methods produce positional
estimates and uncertainty ellipses even in the face of the substantial
degeneracies of short-arc orbit fits; the sole a priori assumption is that the
orbit should be bound or nearly so. We use these orbit-fitting techniques to
derive a strategy for determining Kuiper Belt orbits with a minimal number of
observations.Comment: 21 pages AASTeX5, 3 figures, accepted to AJ. Associated software
available at http://www.astro.lsa.umich.edu/users/gary
Generalized Euler-Poincar\'e equations on Lie groups and homogeneous spaces, orbit invariants and applications
We develop the necessary tools, including a notion of logarithmic derivative
for curves in homogeneous spaces, for deriving a general class of equations
including Euler-Poincar\'e equations on Lie groups and homogeneous spaces.
Orbit invariants play an important role in this context and we use these
invariants to prove global existence and uniqueness results for a class of PDE.
This class includes Euler-Poincar\'e equations that have not yet been
considered in the literature as well as integrable equations like Camassa-Holm,
Degasperis-Procesi, CH and DP equations, and the geodesic equations
with respect to right invariant Sobolev metrics on the group of diffeomorphisms
of the circle
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