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કેપ્લર ના ગ્રહો ના ભ્રમણ નીયમો ધૂમકેતુ ને પણ લાગુ પડવા જોઈએ તેમ સૂચન સૌપ્રથમ [[વિલિયમ લોવર]] એ [[૧૬૧૦]] મા કર્યુ હતુ.{{hnote|ESO, Part I}} આવનારા દશકો મા, અન્ય ખગોળશાસ્ત્રીઓ, જેમા [[પીયરે પેટિટ]], [[જિઓવાન્નિ બોરેલ્લી]], [[એડ્રિયન ઓઝાઉટ]], [[રોબર્ટ હુક]], અને [[જિન-ડોમીનીક કેસ્સીનિ]], ધૂમકેતુs ના સૂર્ય ફરતે દીર્ઘવૃત્તાકાર અથવા પરવલયી કક્ષા મા ભ્રમણ ની તરફેણ મા હતા , જ્યારે અન્ય, જેમ કે [[ક્રિસ્ચીયન હ્યુગીન્સ]] અને [[જોહાન્સ હેવેલીઅસ]], ધૂમકેતુ ના રેખીય ગતિ ના સમર્થન મા હતા .{{hnote|Prasar, Part II}}
The matter was resolved by the [[C/1680 V1|bright ધૂમકેતુ]] that was discovered by [[Gottfried Kirch]] on [[November 14]], [[1680]]. Astronomers throughout Europe tracked its position for several months. In his ''[[Philosophiae Naturalis Principia Mathematica|Principia Mathematica]]'' of [[1687]], [[આઇઝેક ન્યુટન]] proved that an object moving under the influence of his [[inverse square law]] of [[Gravity|universal gravitation]] must trace out an ભ્રમણકક્ષા shaped like one of the [[conic section]]s, and he demonstrated how to fit a ધૂમકેતુ's path through the sky to a [[parabola|parabolic]] ભ્રમણકક્ષા, using the ધૂમકેતુ of 1680 as an example.{{hnote|Newton, Lib. 3, Prop. 41.}}
In [[1705]], [[એઙમન્ઙ હેલિ]] applied Newton's method to twenty-four ધૂમકેતુary apparitions that had occurred between 1337 and 1698. He noted that three of these, the ધૂમકેતુs of 1531, 1607, and 1682, had very similar [[ભ્રમણકક્ષાal element]]s, and he was further able to account for the slight differences in their ભ્રમણકક્ષાs in terms of gravitational perturbation by [[ગુરુ (planet)|ગુરુ]] and [[Saturn (planet)|Saturn]]. Confident that these three apparitions had been three appearances of the same ધૂમકેતુ, he predicted that it would appear again in 1758-9. {{hnote|Halley (1705)}} (Earlier, Robert Hooke had identified the ધૂમકેતુ of 1664 with that of 1618, {{hnote|Pepys, 1 March 1664/5}} while Jean-Dominique Cassini had suspected the identity of the ધૂમકેતુs of 1577, 1665, and 1680. {{hnote|Sagan, pp. 42–43}} Both were incorrect.) Halley's predicted return date was later refined by a team of three [[France|French]] mathematicians: [[Alexis Clairaut]], [[Joseph Lalande]], and [[Nicole-Reine Lepaute]], who predicted the date of the ધૂમકેતુ's 1759 perihelion to within one month's accuracy. {{hnote|Sagan, p. 83}} When the ધૂમકેતુ returned as predicted, it became known as [[ધૂમકેતુ Halley]] or Halley's ધૂમકેતુ (its official designation is '''1P/Halley'''). Its next appearance is due in [[2061]].
Among the ધૂમકેતુs with short enough periods to have been observed several times in the historical record, ધૂમકેતુ Halley is unique in consistently being bright enough to be visible to the naked eye. Since the confirmation of ધૂમકેતુ Halley's periodicity, many other periodic ધૂમકેતુs have been discovered through the [[telescope]]. The second ધૂમકેતુ to be discovered to have a periodic ભ્રમણકક્ષા was [[ધૂમકેતુ Encke]] (official designation '''2P/Encke'''). Over the period [[1819]]-[[1821]] the [[Germany|German]] mathematician and physicist [[Johann Franz Encke]] computed ભ્રમણકક્ષાs for a series of ધૂમકેતુary apparitions observed in 1786, 1795, 1805, and 1818, concluded they were same ધૂમકેતુ, and successfully predicted its return in [[1822]].{{hnote|Kronk, '2P/Encke'}} By 1900, seventeen ધૂમકેતુs had been observed at more than one perihelion passage and recognized as periodic ધૂમકેતુs. As of January 2005, 164 ધૂમકેતુs have achieved this distinction, though several have since been destroyed or lost.
=== બાહ્ય લાક્ષણીકતાઓનુ અધ્યયન ===
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