S. Segan

University of Belgrade · Faculty of Mathematics

This Almanac contains ephemerides at an interval of two hours and auxiliary astronomical data for marine navigation and other astronomical data of general interest.

The paper considers the calendar as a link between the cosmos and mankind, and itintroduces it as an instrument in studying culture. It uses the concept of calendars/calendar systemsas a criterion for recognition and formation of culture in general. Starting from an assumption thatthe calendar is a structurally organized system of events or holiday...

DATA FOR ASTRONOMY AND ASTRONOMICAL NAVIGATION.

The nautical almanac for the year 2020 contains ephemerides at an interval of two hours and auxiliary astronomical data for marine navigation.

The nautical almanac for the year 2018 contains ephemerides at an interval of two hours and auxiliary astronomical data for marine navigation.

The aim of the paper is to present the digitization of the results of last observations of bright stars made by the Belgrade vertical circle ASKANIA N±80118 (D = 190 mm, f = 2578 mm) at the Astronomical Observatory of Belgrade. The observations are mainly made by Djuro Bozhichkovich in the period between 1982 and 1985. All of the found observationa...

The report studies some changes in orbital elements of the artificial satellites of Earth under influence of atmospheric drag. In order to develop possibilities of applying the results in many future cases, an analytical interpretation of the orbital element perturbations is given via useful, but very long expressions. The development is based on t...

This almanac contains ephemeris data of the Sun, planets and Moon on every 2 hours for every calendar day of the 2017. year. Also the ephemeris of 54 nautical stars for every first day of the month are given. There are all the necessary auxiliary tables for the purposes of navigation by using ephemeris of the celestial bodies. There are separate...

The possibility of meteoroid impact is one of the main threats to the interplanetary missions. Although the meteoroids in the interplanetary space have very small masses, their velocities are extremely large and can produce highly energetic impacts. In this paper, a specific method to analyze the meteoroid environment on the transfer trajectories t...

Attention in this work is focused on aerodynamic heating and aero-thermo-mechanical analysis of fin type structures on the missile at supersonic flight. At high Mach number the heat due to friction between body and flow, i.e. viscous heating must be taken into account because the velocity field is coupled with the temperature field. The flow field...

Quasi-thermal noise (QTN) spectroscopy is a plasma diagnostic technique which enables precise measurements of local electron velocity distribution function moments. This technique is based on measurements and analysis of voltage fluctuations at the antenna terminals, induced by thermal motion of charged particles. In this work, we accommodate, for...

Quasi-thermal noise (QTN) spectroscopy is an accurate technique for in situ measurements of electron density and temperature in space plasmas. A QTN spectrum is determined by plasma and antenna properties. On STEREO/WAVES, since the antennas are relatively short and thick, the QTN spectrum is dominated by electron shot noise, especially at low freq...

This almanac contains ephemeris of the sun, planets, moon, every 2 hours for the 2016 year and the ephemeris 54 nautical stars on every first day of the month. There are all the necessary auxiliary tables for the purposes of navigation with celestial bodies. In a separate tables are given ephemeris data for Polaris. For easier selection and orienta...

The phenomena like high eccentricity of Martian orbit, obliquity of the orbital plane and close alignment of the winter solstice and the orbital perihelion, separately or together can significantly alter not only the level of some Martian atmospheric parameters but also the characteristics of its diurnal and seasonal cycle. Considering that entry,...

Due to the high eccentricity of Mars orbit, which is almost six times larger than the Earth's, there are large differences in energy received from the Sun throughout a Martian year. This difference between the perihelion and aphelion on Mars orbit is more than 45%, comparing to less than 7% for the Earth. This big difference and near coincidence of...

This paper gives the analysis and the solution to a radio interferometric array - SCMA (Serbian Centimeter/Millimeter Array). SCMA will be made of three experimental dish antennas, with an aim to study the high energy processes mainly in the Solar atmosphere, by application of detection and localization in the microwave frequency range (1-50 GHz)....

In this paper, we expose general performance of navigation, compared and opposed to astrodynamics and marine navigation, observing methods for determining the orbit and operating in the Space and on the Earth and, also, pre-satellite and post-satellite era of cosmic navigation.

In this paper we consider moving bodies with variable mass. Such kind of motion often occurs in nature and technology. We derived an equation of motion of bodies with variable mass in general case and by the example of rocket motion. Basic and some specific equations are given to describe such movement.

To increase energy resources, and thus the overall possibility of modern cosmic aircrafts, power supply was expanded by adding the (moving) wing area and antenna with complex orientation and design. It is clear that all of this, when there is a need to conduct a very accurate account of orbital elements of satellites, is a nightmare for the experts...

Our main aim is to apply the theory of regularly varying functions to the asymptotical analysis at infinity of solutions of Friedmann cosmological equations. A new constant Γ is introduced related to the Friedmann cosmological equations. Determining the values of Γ we obtain the asymptotical behavior of the solutions, i.e. of the expansion scale fa...

This paper presents the distributions of the positions of the Minimal Orbit Intersection Distances (MOID) among three subgroups of the Near Earth Asteroids (NEAs). This includes 683 Atens, 4185 Apollos and 3538 Amors which makes over 15 millions combinations of the pairs of orbits. The results which are obtained in this analysis show very interesti...

This paper presents the influence of the variations in the Earth’s atmosphere on the physical and chemical processes, such as dissociation, ionization, ablation and fragmentation, encountered during the entry of a meteoroid.

We discuss solutions of the acceleration equation, the equation associated to the Friedman equation, in the light of the theory of regularly varying functions, also known as Karamata functions. As a result we obtain that the solutions of the acceleration equation might have a multiplicative term which is a slowly varying function. Under usual assum...

We describe a simple and efficient numerical-analytical method to find all of the proximities and critical points of the distance function in the case of two elliptical orbits with a common focus. Our method is based on the solutions of Simovljević's (1974) graphical method and on the transcendent equations developed by Lazović (1993). The method i...

To improve the digital connection among Islamic and Christianity heritage in the Balkan region, we have developed several procedures for reconstruction oldest calendric rules of both confessions. Also, one part of the paper refers to the islamic prayer schedule calculation. This possibility is produced from an original algo-rithm for high accuracy...

In this paper we have examined possibilities for preserving and improving the total density model of the Earth's neutral thermosphere TD88 (Sehnal and Pospisilova 1988) via modelling differences between TD88 and NRLMSISE-00 (Picone et al. 2002), which is used as a control model. It is shown that these residuals can be approximated with polyhar...

In order to estimate the accuracy of satellite orbit predictions, perturbations of some orbital parameters were determined using three different atmospheric density models: CIRA86, NRLM-SIS00 and TD-88Ip. The drag coefficient applicable to a specific phase of the satellite flight was obtained by fitting an appropriate set of two-line orbital elemen...

We discuss solutions of the acceleration equation, the equation associated to the Friedman equation, in the light of the theory of regularly varying functions, also known as Karamata functions. As a result we obtain that the solutions of the acceleration equation might have a multiplicative term which is a slowly varying function. Under usual assum...

Using observational data available for a large number of Galactic Cepheids, we determine the relation between the radius and the period of pulsations, by means of a variant of the Baade-Wesselink method. Using, further, the brightness parameter according to the Barnes-Evans approach, we achieve our final goal, determination of the relation between...

In the age of intensive exploring of the solar system, many professionals and non-professionals become interested in calculating the basic data regarding the solar system planets. We have considered some concepts of the physical ephemeris calculation for the natural and artificial solar system bodies. As an effective result, during a conference ses...

In this article we try to answer the question how and why did Chinese ancient astronomy came into being and how did one lonesome and original calendar system on the very end of the world develop. At the beginning, Chinese people distinguished time of the year by the annual cycles of plants and animals, but soon began to determine seasons by observi...

Improved constants of the total density TD-88 model for the Earth's neutral thermosphere are calculated. The model is fully functional within the height range of 200 to 500 km, with fixed values of the mean solar flux and geomagnetic index. The control data of the atmospheric air density are derived from the aeronomical NRLMSISE-00 model which was...

We present an extended analysis of the relation between radio surface brightness and diameter - the so-calledD relation for planetary nebulae (PNe). We revise our previous derivation of the theoreticalD relation for the evolution of bremsstrahlung surface brightness in order to include the influence of the fast wind from the central star. Different...

We present an extended analysis of the relation between radio surface brightness and diameter - the so-called Sigma-D relation for planetary nebulae (PNe). We revise our previous derivation of the theoretical Sigma-D relation for the evolution of bremsstrahlung surface brightness in order to include the influence of the fast wind from the central s...

We examine the possibility to extend leap second extrapolation for a near future based on some periodic terms in the Earth's rotation changes. The IERS data, covering the interval from 1962.15 to 2006.95, are analyzed. The difference $\Delta T$ is extrapolated till to 2035 and compared with the IERS extrapolated values to the 2012. It can be seen t...

Cultural and scientific importance of AOB astronomical observation digitalization recorded at observation forms. One solution for on-line and off-line data input and observational data access. Recalculation and control of obtained results. Example of observation reduction performed by Time service on little passage instrument (D=100 mm, F=1000 mm)....

It has been shown in selecting of the methods for the separating of periodic components that a very efficient use of the method of ordinate transformation is possible. Here an algorithm for generating almost arbitrary amplitude multipliers and their complexes is presented. The applicability limits are interactively variable. The algorithms are asso...

The first version of en electronic encyclopedia in the Serbian language is presented. The localization problem (especially the Cyrillic letters and historical terminology) is mentioned as well. The basic tools for realizing such a project are described.

A review of calendars and their properties in use is presented. The presence of a non-astronomical approach in recent times is emphasized. Here a calendar project is presented which would realize one of the main objectives: an easy historical identification and a minimal necessity for the presence of astronomy in their maintenance.

General requirements and a review of existing approximations of discrete functions are given. Some AMMCO (Amplitude Multiplicators of Multi-Composing of Ordinates) are applied to selected theoretical examples and the results are compared with those obtained by using classical models. Using the shadow function we demonstrate the usability of these a...

The most recent atmosphere models usable in the theory of Earth Artificial Satellites (EAS) motion are analysed. The advantage of the so-called total-density models in the cases of application to the calculation of perturbations in the EAS motion caused by the atmosphere drag is indicated. The parameters of our own model obtained for the perigee di...

The usual common approach for classification of eclipses is via apparent distribution of objects. By using computer based environment we have realized a new approach. The idea behind this new approach is to form celestial triplets based on the spatial and electromagnetic characteristics. If we include observer position, this approach results in ver...

A complex software for preparation and treatment of astro photographic plates and double-star observations recorded with CCD cameras is developed. The preparation interface contains a catalogue base for the choice of observation objects and an interface for bringing into accordance the telescope and CCD camera performance with the assumptions of th...

There is a relative long and occasionally dissonant teaching of Astronomy in Serbia. The history of this theme is discussed in details. We read about "ups" and "downs" of astronomy in the literature and about possible historical reasons for this. We see that it is important for astronomers to be included in broad curriculum planning. We also discus...

In this paper we examine air densities derived from our realization of aeronomic atmosphere models based on accelerometer measurements from satellites in a low Earth's orbit (LEO). Using the adapted algorithms we derive comparison parameters. The first results concerning the adjustment of the aeronomic models to the total-density model are given.

Using the method of multi-composing of ordinates we have identified in Earth's rotation a long-periodic term with a period similar to the relaxation time of Chandler nutation. There was not enough information to assess its origin. We demonstrate that the method can be used even in the case when the data time span is comparable to the period of harm...

In this paper we describe a method of plain and multi composing of ordinates to define spectral filters. We apply the method to the simulated equidistant observations, and we find that the suitable filters are easy to construct and apply.

The general expressions for the scale heights in aeronomic atmospheric density models are given.

The spectral analysis of the ILS polar motion data in the interval 1900 - 1980 is accomplished. The obtained results are discussed and compared with results of other authors. The authors conclude that two resonant frequencies in the Chandler wobble do not exist, but only one modulated.

Under conditions of the "total density model" (Sehnal, 1988) the changes of the satellite orbital elements are concluded (Segan, 1989) and first and second order theories are constructed. The authors assume that the constants defining thermospheric density model are small (parameters).

An analytical interpretation of the satellite orbital element perturbations under influence of a drag has been developed. Some useful formulas for the perturbations of the semi-major axis are given. The agreement with observed values is very good.

A special FORTRAN program has been developed for the computation of satellite orbital eccentricity perturbations. A comparison with the observed values is also given.

Introductory description and BASIC program for the calculation of lunar eclipses are given.

An analytical interpretation of the satellite orbital element perturbations under influence of a drag has been developed. Some useful formulae for the perturbations of the semi-major axis are given. The agreement with observed values is very good.

Corrections of right ascensions of 297 stars are determined from observations with the small transit instrument of Belgrade Observatory in the period 1969 - 1979. The systematic errors of the type Δαδ is varying by 0s.025; systematic errors Δαα are of the order of 0s.01. This agrees well with the results obtained elsewhere.

We present an extended analysis of the relation between radio surface brightness and diameter – the so-called $\Sigma-D$ relation for planetary nebulae (PNe). We revise our previous derivation of the theoretical $\Sigma-D$ relation for the evolution of bremsstrahlung surface brightness in order to include the influence of the fast wind from the cen...