Vulpecula Constellation Map

صورة

الشرح: The constellation Vulpecula with its brighter stars and surrounding constellations. Vulpecula is surrounded by (going clockwise from the top): Cygnus, Lyra, Hercules, Sagitta, Delphinus and Pegasus. Vulpecula is a northern constellation and thus the whole constellation is visible at some point in the year throughout the northern hemisphere. The whole constellation is also visible in equatorial and temperate regions of the southern hemisphere. Vulpecula is best viewed in the evening in the northern hemisphere early autumn and southern hemisphere early spring. The planetary nebula M27, commonly known as the Dumbbell Nebula lies in Vulpecula and is marked here with a green cross superimposed on a plus sign. The open cluster NGC 6885 also lies in Vulpecula and is marked here with a yellow circle. The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labeled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. Neither the constellation boundaries, nor the lines joining the stars appear on the sky.
المصدر: Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope
رابط المصدر

مصطلحات المعجم: القدرالظاهري , الإحداثيات السماوية , مجموعة نجمية او حشد نجمى , الميل , السديم الكوكبي , المطلع المستقيم , العنقود المفتوح
فئات: علم الفلك بالعين المجردة

الترخيص: المشاع الإبداعي نَسب المُصنَّف 4.0 دولي (CC BY 4.0) المشاع الإبداعي نَسب المُصنَّف 4.0 دولي (CC BY 4.0) أيقونات

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Tucana Constellation Map

صورة

الشرح: The constellation Tucana with its bright stars and surrounding constellations. Tucana is surrounded by (going clockwise from the top): Grus, Indus, Octans, Hydrus, Eridanus and Phoenix. Tucana is a southern constellation and thus the whole constellation is visible at some point in the year throughout the southern hemisphere. The whole constellation is visible to some equatorial regions of the northern hemisphere with parts of the constellation visible to the remaining northern equatorial regions. Tucana is best viewed in the northern hemisphere autumn and southern hemisphere spring. The Small Magellanic Cloud (SMC), a satellite galaxy of the Milky Way lies in Tucana with a small part spilling over into the neighbouring constellation of Hydrus. The SMC is marked here with a green loop in the south east of Tucana. The globular clusters NGC 104, also known as 47 Tucanae or 47 Tuc, and NGC 362 lie in Tucana and are marked here with yellow circles with plus signs superimposed on them. While these two clusters appear close to the SMC on the sky, they are both significantly closer than that satellite galaxy. The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labeled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. Neither the constellation boundaries, nor the lines joining the stars appear on the sky.
المصدر: Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope
رابط المصدر

مصطلحات المعجم: القدرالظاهري , الإحداثيات السماوية , مجموعة نجمية او حشد نجمى , الميل , العنقود النجمي الكروي , المطلع المستقيم , سحابة ماجلان الصغيرى
فئات: علم الفلك بالعين المجردة

الترخيص: المشاع الإبداعي نَسب المُصنَّف 4.0 دولي (CC BY 4.0) المشاع الإبداعي نَسب المُصنَّف 4.0 دولي (CC BY 4.0) أيقونات

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Annual Parallax

صورة
أُنشئ لصالح OAE

الشرح: Distance determination has historically been a challenge for astronomy. One of the primary ways to measure distance is to use annual parallax. The Earth orbits around the Sun over the course of a year meaning that it moves from one side of the Sun (shown here as position A) to the other side of the Sun (position B) over the course of six months. It then moves back to its original position over the remaining six months. This movement subtly changes the perspective an observer on Earth sees the night sky from. This is similar to the change in viewing perspective you may get when viewing a scene from your left eye and then your right eye. The change of viewing perspective causes nearby objects to shift in position in your vision. The annual motion of the Earth around the Sun changes the perspective of the observer enough to shift the observed positions of celestial objects. How big this effect is depends on the distance to the celestial object. Nearby stars will have bigger shifts in observed position than more distant stars. The positional shift is known as the trigonometric or annual parallax (which we will call α here) and is defined as the shift in position of a star compared to what an observer at the center of the Solar System (the Sun) would see. In this diagram we see the star viewed from perspectives six months apart (positions A and B). When observed from position A the star’s shift in position will be α while when observed at position B it will be –α. Thus the relative difference in the stars position between being observed at position A and position B will be 2α. The size of the trigonometric or annual parallax in arcseconds is approximately 1 divided by the distance in parsecs. An arcsecond (often represented by a ″ symbol) is the angular diameter a one-metre-long stick would have when viewed from 206 km away. A parsec (often abbreviated to pc) is 3.26 light years or 30.86 trillion kilometres. This is 206,265 astronomical units (the typical distance between the Earth and the Sun). No other star is closer than 1 pc to the Sun so all stars in the sky have trigonometric parallaxes less than one arcsecond. While trigonometric parallaxes have long been used to measure the distances to objects in our Solar System or nearby stars, recent advances have pushed the boundaries of these distance measures further. The Gaia satellite has pushed the boundaries of parallax measurements to over a thousand parsecs. Arrays of radio telescopes can also very accurately measure the positions of very distant objects and thus their trigonometric parallax. Note the Earth and Sun are not to scale here and the Earth’s axial tilt is not accurately represented.
المصدر: Aneta Margraf/IAU OAE

مصطلحات المعجم: القطر الزاوي , اختلاف المنظر السنوي , الوحدة الفلكية , زاوية إختلاف المنظر
فئات: علم الفلك الرصدي

الترخيص: المشاع الإبداعي نَسب المُصنَّف 4.0 دولي (CC BY 4.0) المشاع الإبداعي نَسب المُصنَّف 4.0 دولي (CC BY 4.0) أيقونات

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Celestial Coordinates

صورة
أُنشئ لصالح OAE

الشرح: Here we see how celestial coordinates map positions on the celestial sphere. The celestial sphere is an imaginary, hollow sphere that surrounds the Earth. Celestial objects appear to be attached to the inside of the celestial sphere, and the planets, Sun, and Moon appear to move slowly across it. The celestial sphere has a spherical coordinate system similar to the latitude and longitude we see on the Earth. The celestial equator is the projection of the Earth's equator onto the celestial sphere while the north and south celestial poles are the projections of the Earth's north and south poles onto the celestial sphere. Declination is similar to latitude on the Earth in that it marks the angle above and below the celestial equator. Declination is zero on the celestial equator, is positive to the north of the celestial equator and negative to the south of it. It is commonly measured in degrees and sometimes in radians. Right Ascension is similar to longitude as it marks the angle around the celestial equator. As with longitude the zero point of right ascension (shown here as a dashed line) is a matter of choice. Traditionally the zero point of right ascension was the position of the Sun at the northern hemisphere vernal equinox (spring equinox) in March. It is positive and increases to the east, unlike longitude on Earth which is defined as east or west of the prime meridian. It is most commonly measured in hours, minutes and seconds or occasionally in degrees or radians. The ecliptic marks the Sun's path across the celestial sphere when viewed from the Earth. The Earth rotates within the celestial sphere. This leads to objects like stars or galaxies, which appear static on the celestial sphere, rising and setting when viewed from the Earth but remaining in the same position on the celestial sphere. The Earth's axis precesses within the celestial sphere. This slowly moves the celestial equator and the celestial poles meaning that the traditional celestial coordinate system changes slowly over time meaning that stars and galaxies that do not move will have positions that change. Astronomers have used coordinate systems defined by the position of the celestial poles and equator at a fixed point in time. Now celestial positions are most commonly measured on a fixed coordinate system defined by the position of the celestial poles and equator on the 1st of January 2000.
المصدر: Maria Cristina Fortuna/IAU OAE

فئات: علم الفلك بالعين المجردة , علم الفلك الرصدي

الترخيص: المشاع الإبداعي نَسب المُصنَّف 4.0 دولي (CC BY 4.0) المشاع الإبداعي نَسب المُصنَّف 4.0 دولي (CC BY 4.0) أيقونات

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