International Journal of Scientific & Engineering Research Volume 8, Issue 10, October-2017 1369 ISSN 2229-5518 Investigating the radiant sources of meteors Anamol Mittal, Dr. K. Kishore Kumar Abstract— The results obtained in the present study, which are related to basic meteor phenomenon such as meteor velocity distribution, height distribution and annual variability of meteors are discussed. An attempt is also made to identify the peak radiant sources of the observed meteors. The results are found to be consistent with the present understanding of the meteor phenomenon. Further studies are required to estimate the orbits of the meteors using single station observations. The important outcome of the present study is the algorithm for estimating the radiant sources using azimuth, zenith angle observations of meteor radar. Index Terms— Astronomy, earth sciences, entrance velocity distribution, meteor wind radar, meteors, radiant sources, Thumba —————————— —————————— 1 INTRODUCTION eople have always wondered about the worlds that lie 3. Epoch: In astronomy, an epoch is a moment in time P beyond the boundaries of sky, the purpose of our exis- used as a reference point for some time-varying as- tence, whether the existence of earth is a result of some tronomical quantity, such as the celestial coordinates higher purpose or just a lucky coincidence? Well, answers to or elliptical orbital elements of a celestial body, be- these questions are not known and beyond the reach of present technology. One such question asks: Where do the cause these are subject to perturbations and vary with meteoroids (most commonly known as falling stars) come time.[2] from and how is their distribution in solar system related to the formation of planets and other solar system bodies? You may find answers to these questions as you proceed through the report. 1.1 Some Fundamental concepts: 1. Equinox: Equinox is the intersection of the planes of the earth's equator and the earth's orbit, the ecliptic. The time when the Sun crosses the plane of the earth’s equator, making night and day of approximately equal length all over the earth land occurring on about March 21 (vernalIJSER equinox) and Sept. 22 (au- tumnal equinox). [1] 2. Local Meridian: The Local Meridian is an imaginary Great Circle on the Celestial Sphere that is perpendi- cular to the local Horizon. It passes through the North point on the Horizon, through the Celestial Pole, up Figure 2: Representation of meridian to the Zenith, and through the South point on the Ho- Source: http://www.aenigmatis.com/ rizon. 1.2 Horizontal coordinate system: The horizontal coordinate system is a celestial coordi- nate system that uses the observer's local horizon as the fundamental plane. It is expressed in terms of azimuth and altitude (or elevation) angle. [3] 4. Azimuth: The vector from an observer (origin) to a point of interest is projected perpendicularly onto a reference plane; the angle between the projected vec- tor and a reference vector on the reference plane is called the azimuth. 5. Zenith distance: Zenith refers to an imaginary point directly "above" a particular location, on the imagi- Figure 1: Representation of Equinox nary celestial sphere. Therefore Zenith distance is the Source:https://victoriastaffordapsychicinvestigation.fi les.wordpress.com/ IJSER © 2017 http://www.ijser.org International Journal of Scientific & Engineering Research Volume 8, Issue 10, October-2017 1370 ISSN 2229-5518 angular distance from Zenith to the point of interest with center being the observer. 6. Altitude (Alt): Sometimes referred to as elevation, is the angle between the object and the observer's local horizon. Alternatively, zenith distance, the distance from di- rectly overhead (i.e. the zenith) may be used instead of altitude. The zenith distance is the complement of altitude (i.e. 90°-altitude). Figure 4: Equatorial coordinate system Source: https://en.wikipedia.org/wiki/Right_ascension In astronomy, we are usually concerned about the location of stars and other celestial objects. Since number of days in a month, days in a year, etc. are not constant over time, Figure 3: Horizontal coordinate system so we cannot rely upon these parameters. In order to have Source:https://en.wikipedia.org/wiki/Horizontal_coordinate_systemIJSER a well-defined and systematic unit system which does not 1.3 Equatorial coordinate system change over time, we define some entirely new terms and 7. Hour Angle: Hour angle is defined as the angular dis- concepts to help measure the exact position of a celestial tance on the celestial sphere measured westward object. along the celestial equator from the meridian to the hour circle passing through a point.[4](Note: an ob- 1.4 Time Depictions 10. Julian date: The Julian Day Count is a uniform count ject's hour Angle indicates how much sidereal time of days from a remote epoch in the past (4714 BCE has passed since the object was on the local meridian). November 24, 12 hours GMT). At this instant, the Ju- lian Day Number is 0. It is convenient for astronomers 8. Declination: Declination's angle is measured north or to use since it is not necessary to worry about odd south of the celestial equator, along the hour circle numbers of days in a month, leap years, etc. Once you passing through the point in question.[4] have the Julian Day Number of a particular date in history, it is easy to calculate time elapsed between it 9. Right ascension: It is the angular distance measured and any other Julian Day Number. Note that the Ju- eastward along the celestial equator from the vernal lian day at the beginning of any day always gives you equinox to the hour circle of the point in question.[4] a half day extra. That is because the Julian Day begins at noon, Greenwich time. 11. Sidereal time: Sidereal time (star time) is a "time scale that is based on the Earth's rate of rotation measured relative to the fixed stars"[5] rather than the Sun. IJSER © 2017 http://www.ijser.org International Journal of Scientific & Engineering Research Volume 8, Issue 10, October-2017 1371 ISSN 2229-5518 Common time on a typical clock measures a slightly longer cycle, accounting not only the Earth’s axial ro- tation but also for the Earth’s annual revolution 1.5 Basic definitions of Meteors and Meteoroids around Sun of slightly less than 1 degree per day. 14. Meteoroids: They are small chunks of rocks floating This creates a vacancy for a timescale which removes in outer space with speeds of about 20 km/sec on an all the complications of Earth’s orbit around sun, and average. just focuses on how long does the earth takes to spin 360 degrees with respect to the stars. Hence, sidereal Meteoroids occurring in the solar system may have time scale was invented. many sources, of which mainly are: asteroids, comets, Note: A mean sidereal day is 23 hours, 56 minutes, and ejections from planetary impacts of asteroids. 4.0916 seconds 0.99726958 mean solar days), the time 15. Meteoroids’ Orbits: Meteoroids may travel in elliptic- it takes the Earth to make one rotation relative to the vernal equinox. al as well as circular orbits around the sun. Some meteoroids travel in clusters which are remnants of comets orbiting sun in elliptical orbits while rest of them travel in different speeds in different orbits, called as sporadic meteoroids. 16. Meteors: When a meteoroid enters the earth’s atmos- phere, a sudden streak of light is produced and this phenomenon is called meteor. The streak of light is caused by the intense heating produced by the air friction on meteoroid’s surface upon entry into the earth’s atmosphere. Commonly, this streak of light is called as a falling star. Meteor may be classified into two categories: • Sporadic meteors: Sporadic meteors originate from random chunks of dust floating around Figure 5: Representation of sidereal time and equatorial the Sun. Their occurrence is random. coordinate system. • Shower meteors: Shower meteors originate http://plato.acadiau.ca/ from dusts left by the comets as they orbit 12. Local Sidereal time (LST): Local Sidereal Time indi- IJSERaround the Sun in their elliptical orbit. The cates the Right Ascension on the sky that is currently dust spreads out along the comet’s orbit and crossing the Local Meridian. So, if a star has a Right forms an elliptical trail of debris that passes Ascension of 05h 32m 24s, it will be on your meridian around the sun and crosses the orbits of pla- at LST=05:32:24. nets.Meteor shower occurs when Earth passes through the trail of debris during its More generally, the difference between an object's RA yearly orbit around sun. and the Local Sidereal Time tells you how far from the Meridian the object is. 17. Radiant position of meteor: The radiant or apparent For example, the same object at LST=06:32:24 (one Si- radiant of a meteor shower is the point in the sky, dereal Hour later), will be one Hour of Right Ascen- from which (to a planetary observer) meteors appear sion west of your meridian, which is 15 degrees. This to originate.[6] angular distance from the meridian is called the ob- ject's Hour Angle. Meteor showers get their names from the constella- tion in where their radiant is located. Perseids come from Perseus, hence the name Perseids. [7] 13. Greenwich mean sidereal time (GST): Greenwich mean sidereal time indicates the right ascension on the sky that is currently crossing the Greenwich meri- 1.6 Objectives of the present study dian. It is related to Local sidereal time by the equa- tion: The present study aims at bringing out the salient fea- GST= LST+ Longitude of the observer tures of meteor activity over Thumba using radar ob- Note: Longitude=+ve (East) and -ve (West) IJSER © 2017 http://www.ijser.org International Journal of Scientific & Engineering Research Volume 8, Issue 10, October-2017 1372 ISSN 2229-5518 servations in terms of variability of meteor counts at • Maximum duty cycle • Up to 15% diurnal and annual scales, their height distribution • Pulse width • Programmable between 1 and meteor entrance velocity distribution.