Solstices and Equinoxes

Bild
Erstellt für das OAE

Unterschrift: 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.
Bild: Maria Cristina Fortuna/IAU OAE

Glossar-Begriffe: Tagundnachtgleiche , Himmelsäquator , Jahreszeiten , Sonnenwende , Sommersonnenwende , Wintersonnenwende , Frühlings-Tagundnachtgleiche , Herbst-Tagundnachtgleiche , Erdachse , Nördlicher Polarkreis , Südlicher Polarkreis , Polartag , Polarnacht
Kategorien: Astronomie mit bloßem Auge

Lizenz: Creative Commons Namensnennung 4.0 International (CC BY 4.0) Creative Commons Namensnennung 4.0 International (CC BY 4.0) Symbole

Datei ( Bild 2.02 MB)
PDF-Datei (PDF file 335.83 kB)

Also available in black and white
Datei ( Bild 485.38 kB)
PDF-Datei ( 388.16 kB)

Hydra Constellation Map

Bild

Unterschrift: The constellation Hydra with its bright stars and surrounding constellations. Hydra is surrounded by (going clockwise from the top): Leo, Cancer, Canis Minor, Monoceros, Puppis, Pyxis, Antlia, Centaurus, Lupus, Libra, Virgo, Corvus, Crater and Sextans. Hydra is a large constellation that covers over a quarter of the celestial sphere in right ascension. It also spans the celestial equator and thus part of the constellation is visible from everywhere on the Earth at some point in the year. All parts of the constellation are visible at some point for all but the most antarctic parts of the southern hemisphere and to equatorial and most temperate regions of the northern hemisphere. However the wide span of the constellation means that all of it may not be visible at the same time in many of these regions. Hydra is best viewed in the northern hemisphere spring and southern hemisphere autumn. The famous spiral galaxy M83, also known as the Pinwheel Galaxy, lies in Hydra. It is marked here with a red ellipse. The planetary nebula NGC 3242 can also be found in Hydra. It is marked here with a green circle with a plus sign superimposed on it. The open cluster M48 is marked here with a yellow circle while the globular cluster M68 is marked with a yellow circle with a plus sign superimposed on it. 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. The blue line on the diagram marks the ecliptic. Neither the constellation boundaries, nor the line marking the ecliptic, nor the lines joining the stars appear on the sky.
Bild: Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope
Link zur Quelle

Glossar-Begriffe: Scheinbare Helligkeit , Himmelskoordinaten , Sternbild , Deklination , Ekliptik , Kugelsternhaufen , Waage , Planetarischer Nebel , Rektaszension (RA) , Spiralgalaxie , Krebs , Offener Sternhaufen , Jungfrau
Kategorien: Astronomie mit bloßem Auge

Lizenz: Creative Commons Namensnennung 4.0 International (CC BY 4.0) Creative Commons Namensnennung 4.0 International (CC BY 4.0) Symbole

Datei ( Bild 114.60 kB)
PDF-Datei (PDF file 253.49 kB)

Aquila Constellation Map

Bild

Unterschrift: The constellation Aquila with its bright stars and surrounding constellations. Aquila is surrounded by (going clockwise from the top): Sagitta, Hercules, Ophiuchus, Serpens Cauda, Scutum, Sagittarius, Capricornus, Aquarius and Delphinus. Aquila is most notable for its brightest star Altair. This forms one vertex of the prominent Summer Triangle asterism that is visible in northern hemisphere summer evenings. Aquila spans the celestial equator and thus some part of it is visible from all of the Earth at some point in the year. It is most visible in the evenings in the late northern hemisphere summer and late southern hemisphere winter. 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. The blue line in the lower right of the diagram is the ecliptic. Neither the constellation boundaries, nor the line marking the ecliptic, nor the lines joining the stars appear on the sky.
Bild: Adapted by the IAU Office of Astronomy for Education from the original by IAU/Sky & Telescope
Link zur Quelle

Glossar-Begriffe: Scheinbare Helligkeit , Steinbock , Himmelskoordinaten , Himmelsäquator , Sternbild , Deklination , Ekliptik , Rektaszension (RA) , Wassermann , Asterismus
Kategorien: Astronomie mit bloßem Auge

Lizenz: Creative Commons Namensnennung 4.0 International (CC BY 4.0) Creative Commons Namensnennung 4.0 International (CC BY 4.0) Symbole

Datei ( Bild 95.28 kB)
PDF-Datei (PDF file 175.09 kB)

Eridanus Constellation Map

Bild

Unterschrift: The constellation Eridanus with its bright stars and surrounding constellations. Eridanus is surrounded by (going clockwise from the top): Taurus, Cetus, Fornax, Phoenix, Tucana, Hydrus, Horologium, Caelum, Lepus and Orion. Eridanus is a large constellation that spans a wide range in declination. A small portion of the constellation is in the northern hemisphere with the southern-most point lying at a declination of almost -60°. As it spans the celestial equator, parts of the constellation are visible to the whole Earth at some point in the year. The whole constellation can be observed from northern and southern equatorial regions, southern temperate regions and most of Antarctica. Eridanus is best viewed in the evening in the northern hemisphere winter and southern hemisphere summer. 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.
Bild: Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope
Link zur Quelle

Glossar-Begriffe: Scheinbare Helligkeit , Himmelskoordinaten , Sternbild , Deklination , Rektaszension (RA) , Stier , Orion
Kategorien: Astronomie mit bloßem Auge

Lizenz: Creative Commons Namensnennung 4.0 International (CC BY 4.0) Creative Commons Namensnennung 4.0 International (CC BY 4.0) Symbole

Datei ( Bild 148.42 kB)
PDF-Datei (PDF file 243.47 kB)

Sextans Constellation Map

Bild

Unterschrift: The constellation Sextans with its brighter stars and surrounding constellations. Sextans is surrounded by (going clockwise from the top): Leo, Hydra and Crater. Sextans is a small constellation with relatively few bright stars. Sextans spans the celestial equator and thus parts of the constellation are visible at some point in the year across the Earth. The whole constellation is visible in all but the most arctic and most antarctic regions. Sextans is best viewed in the evening in the northern hemisphere spring and southern hemisphere autumn. The lenticular galaxy NGC 3115 lies in Sextans. It is marked here with a red ellipse. 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. The blue line at the top of the diagram marks the ecliptic. Neither the constellation boundaries, nor the lines joining the stars, nor the ecliptic, appear on the sky.
Bild: Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope
Link zur Quelle

Glossar-Begriffe: Scheinbare Helligkeit , Himmelskoordinaten , Himmelsäquator , Sternbild , Deklination , Ekliptik , Löwe , Rektaszension (RA) , Linsenförmige Galaxie
Kategorien: Astronomie mit bloßem Auge

Lizenz: Creative Commons Namensnennung 4.0 International (CC BY 4.0) Creative Commons Namensnennung 4.0 International (CC BY 4.0) Symbole

Datei ( Bild 73.40 kB)
PDF-Datei (PDF file 153.02 kB)