Draco Constellation Map

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Légende : The constellation Draco with its bright stars and surrounding constellations. Draco is surrounded by (going clockwise from the top): Cepheus, Ursa Minor, Boötes, Hercules, Lyra and Cygnus. Draco is a sprawling northern constellation, parts of which lie close to the celestial north pole. As such the whole constellation is visible at some point in the year from the whole northern hemisphere and a thin sliver of the southern hemisphere near the equator. Parts of the constellation are visible from all other southern equatorial and some southern temperate regions. Draco is best viewed in the evenings in the northern hemisphere summer and southern hemisphere winter. The planetary nebula NGC 6543 (also known as the Cat’s Eye Nebula) lies in Draco. It is marked here with a green circle superimposed on a plus sign. This diagram maps an area around the north celestial pole. Here lines of constant right ascension converge. The right ascension values of these lines are marked on the x-axis above and below the diagram. Some of the lines of constant declination are marked on the y-axis. 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.
Crédit : Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope
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Termes du glossaire: Magnitude apparente , Coordonnées célestes , Étoiles circumpolaires , Constellation , Déclinaison , Pôle céleste nord (PCN) , Nébuleuse planétaire , Ascension droite (AD)
Catégories : Astronomie à l'œil nu

Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes

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Gemini Constellation Map

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Légende : The zodiac constellation Gemini and its surrounding constellations. Starting from the top of the diagram and going clockwise, these are Auriga, Taurus, Lynx, Orion, Monoceros, Canis Minor and Cancer. The brightest stars in Gemini, Castor and Pollux appear in the upper lefthand corner (north-east) of the diagram. In Greek mythology, the stars in this constellation are thought to resemble twins with their arms wrapped around each other, with Castor and Pollux indicating their heads. Gemini lies on the ecliptic (shown here as a blue line), this is the path the Sun appears to take across the sky over the course of a year. The Sun is in Gemini from late June to late July. The other planets of the Solar System can often be found in Gemini. Gemini lies north of the celestial equator and is visible in all but the antarctic regions of the world. Gemini is most visible in the evenings in the northern hemisphere winter and southern hemisphere summer. Just to the right of the foot of the Castor twin is an open cluster of stars (labelled as a yellow circle with a dotted line border), Messier 35, also known as the Shoe-Buckle Cluster. This cluster is spread out over an area roughly the size of the full moon. In addition to this cluster of stars, there is a planetary nebula (labelled as a green circle with four radial spikes) – NGC 2392 – near the celestial equator and just to the left of the Pollux twin. Two variable stars (Mekbuda and Propus; labelled as two concentric circles) can be found in the “legs” of each twin, but are so faint that an observer would need dark skies to see them. 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 labelled 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 line marking the ecliptic, nor the lines joining the stars appear on the sky.
Crédit : Adapted by the IAU Office of Astronomy for Education from the original by IAU/Sky & Telescope
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Termes du glossaire: Magnitude apparente , Coordonnées célestes , Constellation , Déclinaison , Ecliptique , Gémeaux , Ascension droite (AD) , Taureau , Zodiaque
Catégories : Astronomie à l'œil nu

Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes

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Equuleus Constellation Map

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Légende : The constellation Equuleus with its brighter stars and surrounding constellations. Equuleus is surrounded by (going clockwise from the top): Delphinus, Aquarius and Pegasus. It is a relatively small constellation with few bright stars. Equuleus lies just north of the celestial equator and thus the whole constellation is visible at some point in the year to all but the most antarctic regions. Equuleus is best viewed in the evening in the early northern hemisphere autumn and early southern hemisphere spring. 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.
Crédit : Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope
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Termes du glossaire: Magnitude apparente , Coordonnées célestes , Constellation , Déclinaison , Ascension droite (AD) , Verseau
Catégories : Astronomie à l'œil nu

Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes

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Mensa Constellation Map

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Légende : The constellation Mensa with its brighter stars and surrounding constellations. Mensa is surrounded by (going clockwise from the top): Dorado, Hydrus, Octans, Chamaeleon and Volans. Mensa is a faint constellation with relatively few bright stars. Mensa lies close to the south celestial pole and thus the whole constellation is visible at some point in the year throughout the southern hemisphere. The whole constellation is visible to a thin strip of the northern hemisphere around the equator with parts of the constellation visible to some other northern equatorial regions. Mensa is circumpolar in temperate, antarctic and some equatorial regions of the southern hemisphere. Mensa is best viewed in the evenings in the northern hemisphere winter and southern hemisphere summer. The Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way, lies in Mensa and the neighboring constellation Dorado. The outline of the Large Magellanic Cloud is marked here as a roughly circular loop in green. This diagram maps an area around the south celestial pole. Here lines of constant right ascension converge. The right ascension values of these lines are marked on the x-axis above and below the diagram. The solid circle around the pole marks a line of -80° declination with the larger, incomplete circle to the right marking -70° declination. 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.
Crédit : Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope
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Termes du glossaire: Magnitude apparente , Coordonnées célestes , Constellation , Déclinaison , Ascension droite (AD)
Catégories : Astronomie à l'œil nu

Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes

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Solstices and Equinoxes

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Créé pour l'OAE

Légende : This diagram demonstrates the relative positions of the Earth and Sun at the two solstices and two equinoxes. The Earth’s rotation axis is tilted by 23.4° from the axis of its orbit. This means that for half the Earth’s annual orbit around the Sun, the Southern Hemisphere is tilted towards the Sun and the Northern Hemisphere is tilted away from the Sun. During this time the Sun appears to lie below the celestial equator. Due to this at any particular point in the Southern Hemisphere the Sun will appear to be higher above the horizon at a particular time of day and the days will be longer. Conversely during this time, the Sun appears lower in the sky at any particular point in the day in the Northern Hemisphere and the days are shorter. This effect is most pronounced in late December when the Sun appears at its most southerly point in the sky, corresponding to the longest day of the year in the Southern Hemisphere. This normally occurs on the 21st or 22nd of December (UTC), depending on when the most recent leap year was, but can very occasionally occur on the 20th or 23rd of December. This event is known as the December solstice. As the Sun’s rays hit the Southern Hemisphere at a more perpendicular angle during this time, the Southern Hemisphere is typically warmer in this time of year than at other times of year. This is often referred to as summer in temperate and antarctic regions of the Southern Hemisphere and thus the December solstice is known as the summer solstice. South of the Antarctic Circle at this time the Sun never sets and a Polar Day can last several months. Conversely in the Northern Hemisphere, the Sun’s rays hit the Earth at a more grazing angle than at other times of year so it is colder and this solstice is known as the winter solstice. North of the Arctic Circle the Sun never rises during this time and the Polar Night can last several months. As the year progresses the Earth moves in its orbit and the tilt of the Earth’s axis moves so it appears more side-on to the Sun. From the perspective of an observer on Earth this means that the Sun moves north in the sky, eventually reaching the celestial equator in late March, This usually occurs on the 20th of March (UTC) but can sometimes occur on the 19th or 21st of March. During this time all places on Earth will experience night and day that is approximately 12 hours long. The Sun’s rays now hit the Southern hemisphere at a more shallow angle than they did in December and hit the Northern Hemisphere at a more perpendicular angle. This means that the Northen Hemisphere will have warmed since December and the Southern Hemisphere cooled. This leads to the March equinox being referred to as the autumn equinox in the Southern Hemisphere and the spring or vernal equinox in the Northern Hemisphere. As the year progresses further the Sun moves further north on the sky, the Northern Hemisphere days lengthen and the Southern Hemisphere days shorten. By June the Earth’s orbit has progressed to the point where the Northern Hemisphere points towards the Sun and the Southern Hemisphere away from the Sun. At one point between the 20th and 22nd of June (UTC) the Sun reaches its most northerly point in the sky, this is known as June solstice. It is now summer in northern temperate and artic regions so this is known as the summer solstice in the Northern Hemisphere and the winter solstice in the Southern Hemisphere. This is the longest day of the year in the Northern Hemisphere and the shortest day of the year in the Southern Hemisphere. During this time regions north of the Arctic Circle experience a long Polar Day and regions south of the Antarctic Circle experience polar night. The year progresses further and the Earth moves in its orbit so that the tilt of the Earth’s axis again appears side-on for the Sun. The Sun moves south in the sky and again crosses the celestial equator between the 21st and 24th of September (UTC). At this time all places on the Earth experience equal lengths of day and night. This is known as the September equinox, also called the spring or vernal equinox in the Southern Hemisphere and the autumn equinox in the Northern Hemisphere. Note the sizes of the Earth, Sun and the Earth’s orbit around the Sun are not to scale in this diagram.
Crédit : Maria Cristina Fortuna/IAU OAE

Termes du glossaire: Equinoxe , Équateur céleste , Saisons , Solstice , Solstice d'été , Solstice d'hiver , Equinoxe de printemps , Equinoxe d'automne , Axe de la Terre , Cercle arctique , Cercle antarctique , Journée polaire , Nuit polaire
Catégories : Astronomie à l'œil nu

Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes

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