# P. Kenneth Seidelmann's research while affiliated with University of Virginia and other places

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## Publications (97)

From the earliest times astronomical information was used for calendars, time, climate, farming, seasons, and phenomena predictions. The Sun, Moon, five planets, and star patterns were known. Treatises and tables were used to calculate positions of planets. There are records of astronomical data in different forms from different countries. Ptolemy...

The different countries initiated their own almanacs independently. The need for a standard meridian led to the adoption of the Greenwich meridian as the prime meridian. Cooperation and the adoption of international standards began in 1896 and continued thereafter. The establishment of the International Astronomical Union (IAU) provided a continuin...

This edited volume charts the history of celestial navigation over the course of five centuries. Written by a group of historians and scientists, it analyzes how competing navigation systems, technologies, and institutions emerged and developed, with a focus on the major players in the US and the UK.
The history covers the founding of the Royal Obs...

Cambridge Core - Time: From Earth Rotation to Atomic Physics - by Dennis D. McCarthy

The uses of time in astronomy - from pointing telescopes, coordinating and processing observations, predicting ephemerides, cultures, religious practices, history, businesses, determining Earth orientation, analyzing time-series data and in many other ways - represent a broad sample of how time is used throughout human society and in space. Time an...

This book is designed as an introductory text and reference for graduate students, researchers and practitioners in the fields of astronomy, astrodynamics, satellite systems, space sciences and astrophysics. The purpose of the book is to emphasize the similarities between celestial mechanics and astrodynamics, and to present recent advances in thes...

This section is meant as an introduction to notation and procedures involved in numerical work that occurs in celestial mechanics and astrodynamics
. No theoretical developments will be presented; for theory the reader might consult a work
on finite differences. The notation to be used and reference to more information is available from Nautical Al...

A reference system is a theoretical concept of coordinates, and includes the time and the standards necessary to specify the bases for giving positions and motions in the system. There are celestial and terrestrial reference systems

So far we have considered the following problem: Given the elements of the orbit, find the position of the celestial object at any time (Chap.5). Now let us consider the other problem: Given the observations of an object, determine the elements of its orbit. We have considered determining the elements when the position and velocity
are known, but t...

An important particular solution of the three-body problem
results when one of the three masses is so small, in comparison to the other two, that its gravitational effects can be neglected. This may be called an infinitesimal body
compared with the two finite bodies. This is the restricted three-body problem (Szebehely 1967), as mentioned in Sect....

Assume that the masses are spherically symmetrical and homogeneous in concentric layers. So they attract one another as if the mass were concentrated at spherical centers

Now we want to look at a completely different approach to solving the equations of motion, and a different type of variables. We must first establish our notation and the equations of motion which underlie this approach.

When going from two bodies to three, or more, bodies, the complexity increases significantly, due to their mutual attractions. The two-body problem can be mathematically formulated so a closed-form solution is possible. With more than two bodies, it is impossible to formulate such a solution. There are some special cases, however, that can be handl...

An important perturbation affecting low planetary satellites is the planet’s oblateness, approximated mathematically by the second zonal harmonic J
2, discussed in Sect. 11.10 The problem of motion in such a potential field is often referred to as the main problem in artificial satellite theory, and has been the subject of many studies over the yea...

In Chap. 14, we defined the notion of impulsive maneuvers,
used as a common approximation for designing orbital maneuvers. An important orbital maneuver problem is the fuel-optimal impulsive transfer between 2 coplanar circular orbits. Three such transfers are the Hohmann transfer,
discussed in Sect. 14.7.1; the bi-elliptic transfer
; and the bi-pa...

Semianalytical theories provide tools for propagating perturbed satellite orbits. The power of these theories lies in the ability to efficiently calculate, and thereby comprehend, the orbital dynamics of satellites. In many cases of practical interest, as we will see in Chap. 14, satellite orbit control laws also utilize mean orbital elements. The...

This chapter is meant to provide the basic information concerning vectors, hopefully as a review, but to ensure that the reader is familiar with the basics.

Satellite orbit control refers to the process of generating thrust for tracking a particular orbit in the presence of orbital perturbations. The particular orbit is mission dependent. It could be a low Earth orbit (LEO), used for Earth imaging, a geostationary orbit (GEO)
used for communication and weather monitoring, or an interplanetary orbit.

If the force causing accelerated motion of a particle passes through a fixed point, then this yields central force motion

Since 1957, more than 4500 satellites have been launched and over 1000 active satellites are in orbit. The intensive use of the space environment created a large amount of man-made objects in orbit around the Earth, which no longer serve a useful purpose. These objects are commonly referred to as space debris
. Approximately 20,000 objects larger t...

We have seen the complexity of the problem when more than two gravitating masses are involved. We have seen two methods of determining the orbits, Cowell’s and Encke’s methods
. Now, let us look at the basic mathematical description of the perturbation
problem.

In Chap. 9 we discussed numerical procedures for computation of orbits. In this chapter we will discuss other numerical procedures as needed for celestial mechanics and astrodynamics
. These include the processing and filtering
of observations and fitting ephemerides to the observations, determining an approximation for a given set of measurements,...

The developments and progress in celestial mechanics and astrodynamics
can in most cases be tied directly to the scientists who contributed to the ideas and advancements. Some of those people are identified here.

This volume is designed as an introductory text and reference book for graduate students, researchers and practitioners in the fields of astronomy, astrodynamics, satellite systems, space sciences and astrophysics. The purpose of the book is to emphasize the similarities between celestial mechanics and astrodynamics, and to present recent advances...

As part of a reorganization of the International Astronomical Union (IAU),
Commission 4 (Ephemerides) went out of existence after the IAU General Assembly
in August 2015. This paper presents brief discussions of some of the
developments in fundamental astronomy that have influenced and been influenced
by the work of Commission 4 over its 96-year hi...

In 1884, the International Meridian Conference recommended that the prime meridian “to be employed as a common zero of longitude and standard of time-reckoning throughout the globe” pass through the “centre of the transit instrument at the Observatory of Greenwich”. Today, tourists visiting its meridian line must walk east approximately 102 m befor...

Universal Time is the measure of Earth rotation that serves as the astronomical basis of civil timekeeping. Since the end of the 19th century, Universal Time has been maintained to preserve continuity with Newcomb's mean solar time at Greenwich. Here, the concept of a fictitious mean sun is revisited and compared with UT1. Simulations affirm that U...

As in the past, the primary activity of the IAU Working Group on
Cartographic Coordinates and Rotational Elements has been to prepare and
publish a triennial (``2009'') report containing current recommendations
for models for Solar System bodies (Archinal et al. (2011a)). The
authors are B. A. Archinal, M. F. A'Hearn, E. Bowell, A. Conrad, G. J.
Co...

The primary poles for (243) Ida and (134340) Pluto and its satellite (134340) Pluto : I Charon were redefined in the IAU Working
Group on Cartographic Coordinates and Rotational Elements (WGCCRE) 2006 report (Seidelmann et al. in Celest Mech Dyn Astr
98:155, 2007), and 2009 report (Archinal et al. in Celest Mech Dyn Astr 109:101, 2011), respectivel...

Numerous time scales exist to address specific user requirements. Accurate dynamical time scales (barycentric, geocentric and terrestrial) have been developed based on the theory of relativity. A family of time scales has been developed based on the rotation of the Earth that includes Universal Time (specifically UT1), which serves as the tradition...

Before atomic timekeeping, clocks were set to the skies. But starting in
1972, radio signals began broadcasting atomic seconds and leap seconds have
occasionally been added to that stream of atomic seconds to keep the signals
synchronized with the actual rotation of Earth. Such adjustments were
considered necessary because Earth's rotation is less...

Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee...

A recommendation pending before the study groups of the International Telecommuni-cations Union – Radiocommunication Sector (ITU-R) would abolish leap seconds in Coordi-nated Universal Time (UTC). This would have significant near-term consequences to astro-dynamics, astronomy, and other technical fields, and long-term societal and cultural impli-ca...

Future Needs for TimeModeling the Earth's RotationClocks of the FutureFuture Time ScalesFuture Time Distribution

Ephemerides and TimeBefore Kepler and NewtonKepler and NewtonTables, General Theories, and EphemeridesLunar TheoriesThe Advent of ComputersNumerical IntegrationsObservational DataDynamical Reference FrameTime ArgumentsAstronomical ConstantsArtificial Satellite TheoriesTheory of RelativityReferences

Newtonian Reference SystemsSpecial RelativityLorentz TransformationsCoordinate and Proper TimeMinkowski DiagramsTime in Special RelativityGeneral RelativityIAU ResolutionsTime ScalesRelativistic Effects in Time TransferReferences

Universal Time Before 1972Coordinated Universal Time After 1972Leap SecondsUT1UTC WorldwideTime DistributionThe Future of UTC – Leap Seconds or Not?References

The Historical SecondThe Ephemeris SecondThe SI SecondAdopting the SI SecondReferences

Time and International ActivitiesTreaty of the MeterScientific UnionsService OrganizationsReferences

Constructing an Atomic Time ScaleHistory of TAIFormation of TAIStability of TAIDistribution of TAIRelationship of TAI to Terrestrial TimeReferences

Historical Transfer TechniquesTime and Frequency Dissemination ModelingTime and Frequency Dissemination SystemsReferences

Pre 19th CenturySecular VariationIrregular Variations in the Earth's RotationEarly Explanations for the Variable RotationCurrent Understanding of the Earth's Variable RotationConsequencesReferences

Replacing Ephemeris TimeTerrestrial Dynamical Time (TDT) and Barycentric Dynamical Time (TDB)Problems with TDT and TDBNew Reference SystemNew Time ScalesΔT and Ephemeris Time RevisedRelationships Among Coordinate Time ScalesReferences

The Solar SystemPursuit of UniformityPursuit of AccuracyTime and PhenomenaTime and DistanceSpace Mission TimesProper Times at PlanetsPulsars – An Independent Source of Time?References

Earth OrientationVariations in the Earth's OrientationTransforming Between Reference FramesDetermination of Earth OrientationEarth Orientation DataReferences

Terrestrial to Celestial Reference SystemsDetermination of Earth Orientation ParametersEarth Orientation DataReferences

IntroductionKeeping Time in AntiquityThe First Mechanical ClocksPendulum ClocksQuartz Crystal ClocksClock PerformanceReferences

Time Enables the InfrastructurePositioning and Navigation ServicesCommunicationsPower GridBanking and FinanceEmergency ServicesWater FlowSummaryReference

Apparent Solar TimeMean Solar TimeEquation of TimeSidereal TimeWashington Conference of 1884Newcomb's Theory of the SunUniversal TimeCoordinated Universal Time (UTC)Greenwich Mean Time (GMT)Tropical YearBesselian YearReference SystemTime ZonesDaylight Saving TimeReferences

In the BeginningCharacterizing TimeCalendarsAstronomical ObservationsTimekeepingTime EpochsTime TransferRotation of the EarthBeginning the Twentieth CenturyReferences

Beyond Quartz-Crystal OscillatorsPhysics of Atomic ClocksGeneral Structure of Atomic ClocksDevelopment of Atomic ClocksStored Ion ClocksCharacterizing Atomic ClocksReferences

The IAU/IAG Working Group on Cartographic Coordinates & Rotational Elements published its (2006) triennial report containing current recommendations for models for solar system bodies (Seidelmann et al. 2007). P. Kenneth Seidelmann stepped down as chairperson and B. A. Archinal was elected chairperson at the Working Group business meeting that took...

The main goal of the Working Group was to gather astrometric
observations made during the triennum as well as old observations not
yet published in the data base. The WG encouraged the making of new
observations. A Spring School was organized in China in order to teach
the observational techniques of natural satellites to students and young
astrono...

The question of redefining the UTC Time Scale has been under
consideration by the ITU-R Study Group 7A since 1999. The current
definition requires that UTC -UT1 agree within 0.9 second and that this
be accomplished by the introduction of leap seconds. The proposed change
would eliminate the leap seconds.
The DDA gave a report to the AAS Council on...

Filling the need for a book that conveys the current technology as well as the underlying history and physical background, this book tells physicists and engineers how to measure time to the precision required for modern-day use. The authors draw on their longstanding research experience with timekeeping and high-precision measurement to cover the...

The search for extrasolar planets and planet-forming regions is the focus of a number of programs, including the NASA Navigator Program. The ultimate goal of these programs is finding earth-like planets to determine if they are habitable, and search for signs of life. This effort includes both ground and space-based missions, and techniques of astr...

Six small inner satellites of Neptune were imaged in 1989 with Voyager 2. In 1997, we recovered the four outermost with the Hubble Space Telescope (HST) Wide Field Planetary Camera 2 for astrometric, dynamical, and photometric studies. The ring arcs were not detected in our images. Thirteen exposures were taken in each of three HST orbits: two orbi...

We discuss the IAU resolutions B1.3, B1.4, B1.5, and B1.9 that were adopted during the 24th General Assembly in Manchester, 2000, and provides details on and explanations for these resolutions. It is explained why they present significant progress over the corresponding IAU 1991 resolutions and why they are necessary in the light of present accurac...

A Division 1 Working Group on “Nomenclature for Fundamental Astronomy” (NFA) was formed at the 25th IAU GA in 2003 in order to provide proposals for the new nomenclature associated with the implementation of the IAU 2000 resolutions on reference systems. This WG is also intended to make related educational efforts for addressing the issue to the la...

Every three years the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the
directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report
introduces improved values for the pole and rotation rate of Pluto, Charon, and Phoebe, the pole of J...

The 2003 report of the IAU/IAG Working Group on Cartographic Coordinates
and Rotational Elements has appeared in Celestial Mechanics and
Dynamical Astronomy(2005)volume 91, part 3-4, pages 203-215. The Working
Group continues to maintain and update the information for cartographic
coordinates and rotational elements for the Sun, Moon, planets,
sate...

BVI photometry of Triton and Proteus was derived from HST images taken in 1997. The VEGAMAG photometric technique was used. Triton was found to be brighter by a few percent than observations of the 1970's and 1980's, as expected due to the increasingly greater exposure of the bright south polar region. The leading side was also found to be brighter...

Every three years the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the
directions of the north poles of rotation and the prime meridians of the planets, satellites, and asteroids. This report introduces
a system of cartographic coordinates for asteroids and comets. A topographic reference surface f...

The abolition of intercalary (leap) seconds within Coordinated Universal Time (UTC) would create a new civil time standard fundamentally different from solar time. Having no known civil precedent, such a standard would present national governments with certain legal, technical and philosophical questions brought by the abandonment of the long-stand...

Every three years the IAU/IAG Working Group on cartographic coordinates and rotational elements of the planets and satellites revises tables giving the directions of the north poles of rotation and the prime meridians of the planets, satellites, and asteroids. Also presented are revised tables giving their sizes and shapes. Changes since the previo...

The last three years have been marked by changes, highlights and progress. Organizationally, commission 7 has joined Division I and plans proceed for commissions 8 and 24 to merge in 2000. They have had a common vice president during this triennium. Sadly, the Royal Greenwich Observatory was closed after over 200 years, but Her Majesty’s Nautical A...

## Citations

... The present-day increase rate of lunar semi-major axis is 3.808 ± 0.019 cm/year (Williams et al., 2014) and present-day EMD (in terms of semi-major axis of the lunar orbit) is 384,402 km (Murphy, 2013). LOD is precisely measured using very long baseline interferometry and other methods (McCarthy and Seidelmann, 2018); present-day LOD of 23.9345 h (86,164 sidereal seconds) is defined by the present-day Earth mean angular velocity of ϕ 0 = 7.2921150(1) × 10 − 5 rad/s at J2000 (Supplementary Material). EMD and LOD remain poorly known for most of the geological past. ...

... Diagram For Napier's Rules Circular Parts. [14] Napier's Rule has two rules for applying the formula, the rules of the formula: Sine of middle angle = product of tangents of adjacent angles i.e., one of the sine angles is equal to the product of the adjacent tangent angles. ...

... -P. Kenneth Seidelmann in Sec. 7 of [13] Waters' treatise on navigation in the sixteenth and seventeenth centuries [20] discusses the Polaris-latitude connection on pgs. 41 to 50. ...

... The invention of the quantum frequency standard has promoted the revolution in the time and frequency metrology field. In the past 70 years, the development of quantum frequency standard technology has improved the accuracy of time measurement from 10 -11 to 10 -18 or even better, almost one order of magnitude improvement every 10 years [1]. ...

... Stokes had pendulums in mind when thinking about his drag law. Of course, the things that pendulums are good for are clocks; in other words, for telling the time [16,17]. A crucial difference between fluids and granular media is the reason why sand timers or clocks are more prevalent than water clocks in the history of horology. ...

... (UT) [7] was recognized as the time reference of the world then. However, the uneven rotation problem of the Earth can not be ignored. ...

... Innovation according to Prof Eric Van Heck is about "rethinking how companies work, how they do business and how they serve customers". The implementation of innovation begins with a product, services, system, and business model (McCarthy & Seidelmann, 2010)which include: ...

Reference: International Market Business-Juicxy Ent1

... The parameter K > 0 has dimensions of a length to the power of 2/n and contains the temperature implicitly and is governed by the thermal characteristics of a given polytrope. (For all details regarding basic concepts of polytropes, see for instance Ref. [93], also see references Refs. [12,14,22,24,25,94]). Let us start by using Eqs. ...

... Rendering a periodic orbit asymptotically stable employing the control input can be regarded as a very fundamental control problem. The problem statement is motivated by various examples in engineering such as, for example, the control of a satellite motion along a particular mission dependent orbit (Gurfil and Seidelmann (2016)) or in a hybrid setting to realize walking and running motions of bipedal robots (Westervelt et al. (2003)). Moreover, the control problem also arises in the context of Lotka-Volterra equations which describe chemical reactions, predator and pray populations in biology and models in economic theory. ...

Reference: Optimal Stabilization of Periodic Orbits

... The feedback control for orbital transfers has also been investigated 2,4,5,6 , in particular, for missions that exploit the low thrust propulsion. For instance, the Q-law 7,4 has been proposed and extensively studied. ...