Tag Archives: Polaris

Camelopardalis (The giraffe)

Camelopardalis, Till Credner, July 16, 2004.The Greek camelopardalis means giraffe, which comes from camel because of its long neck and leopard because of its spots.  The brightest star in this constellation is 4th magnitude, which can be a challenge to see in a light-polluted urban sky. This is a faint northern constellation that provides the foreground stars in a direction that points away from the flat disk of the Milky Way. This 18th-largest constellation is found between Polaris, The Big Dipper and Cassiopeia, and is best viewed in February when it is high overhead at nightfall. Camelopardalis is also the direction in which Voyager I is headed, but its power source will be long dead when it arrives in that vicinity thousands of years from now. This constellation is also home to May’s Camelopardalids meteor shower.
http://en.wikipedia.org/wiki/Camelopardalis

IAU Camelopardalis chart, IAU and Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), June 5, 2011.

© James R. Johnson, 2014.
jim@jrjohnson.net

Pegasus (A winged horse in Greek mythology)

PegasusThis is a rather bright constellation that is nearly straight overhead at nightfall in November. An imaginary line drawn from Polaris through Cassiopeia to just beyond the zenith brings the viewer to this constellation. The most notable feature of this constellation is not an obvious winged horse, but an asterism known as the Great Square of Pegasus. An inexperienced observer who is accustomed to smaller constellations with denser star groupings might have difficulty perceiving these four widely spaced stars as a square. As the square’s stars are rather bright, and present an almost perfect quadrangle, it tends to be easier to relocate for an observer who has previously spotted this constellation and knows what to expect. The globular star cluster, M15, is the only Messier object in this constellation.
http://en.wikipedia.org/wiki/Pegasus_(constellation)

IAU Pegasus chart, Sky  Telescope magazine Roger Sinnott and Rick Fienberg), June 5, 2011.
IAU Pegasus chart, Sky Telescope magazine (Roger Sinnott and Rick Fienberg), June 5, 2011.

© James R. Johnson, 2014.
jim@jrjohnson.net

Cassiopeia (A Greek mythological queen)

CassiopeiaCassiopeia is named after the vain Greek mythological queen of Aethiopia, the wife of Cepheus and the daughter of Andromeda. This constellation was one of the 48 constellations cataloged by the 2nd century astronomer Ptolemy that remain among the 88 modern constellations. This 25th-largest constellation appears as either a distinct “M” (fall and winter) or “W” (spring and summer) shaped asterism of bright stars that often catches the eye of novice observers who happen to gaze in the right direction. Although it is a northern circumpolar constellation that can be seen year round, it is found high above Polaris in December, which is when it is most easily viewed. This constellation is located opposite of the Big Dipper from Polaris, so try finding it by starting at the Big Dipper, and tracing a line northward (upward) through Polaris until reaching the first grouping of bright stars.

The Milky Way flows through Cassiopeia, and it contains two Messier objects, M52 and M103, both of which are open star clusters. It also contains numerous other NGC objects and two supernova remnants, including Tycho’s Star, a supernova recorded in 1572 by Tycho Brahe, and another remnant of a supernova that was seen 300 years ago. Interestingly, if our sun were observed from Alpha Centuari, our nearest solar neighbor 4 light-years away, it would appear to be located in Cassiopeia.
http://en.wikipedia.org/wiki/Cassiopeia_(constellation)

603px-Cassiopeia_IAU.svg
IAU Cassiopeia chart, IAU and Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), June 4, 2011.

© James R. Johnson, 2014
jim@jrjohnson.net

The Circumpolar Region of the Celestial Sphere

A circumpolar object (star, constellation, deep space object) is one that never sets below the horizon during the Earth’s daily rotation. Any point in the sky that has a declination (degrees of separation from the celestial equator) greater than the observer’s latitude (degrees of separation from the terrestrial equator) will never set below the horizon. If for some reason the Sun ceased to illuminate the sky, a circumpolar object could be seen to circle Polaris once in about every 24 hour period. Cepheus, for instance, is a circumpolar constellation that is oriented with the top of the house-like asterism nearest Polaris. In the September evening sky, Cepheus is high above Polaris, and the “house” appears to be upside down. Over the course of 24 hours, Cepheus will circle Polaris. In six hours, the “house” is horizontal with the top pointing west, in 12 hours it appears upright, but below Polaris, in 18 hours it appears vertical again, this time with the top pointing east. Six months from now in March, Cepheus’ orientation at dusk is the same upright appearance as Cepheus’ 12-hour position in September.

The circumpolar region of the celestial sphere is indicated on the annotated sky map below as the nearly circular region. Two points define this region, the north celestial pole, and the north point on the horizon. The north celestial pole is at the center of the region’s circular border, and all stars on the map circle around this central point as a result of the earth’s daily rotation about its axis. Stars near the pole make small tight circles around the pole, while those out near the drawn circle, but still within the circle, make wider sweeping circles. Those stars outside of the circle also circle the pole, but will dip below the the northern horizon, and are therefore not circumpolar stars.

Sky_Map_Celestial_Zones

© James R. Johnson, 2015.

Cepheus (The King of Aethiopia)

CepheusCCCepheus is named after the Greek mythological King of Aethiopia, who was also Queen Cassiopeia’s husband and Princess Andromeda’s father. This constellation was one of the 48 constellations cataloged by the 2nd century astronomer Ptolemy that remain among the 88 modern constellations. This 27th-largest constellation is a fairly bright and recognizable circumpolar constellation. It is a house-like asterism of fairly bright stars that can be easily found north and east of Polaris in September’s evening skies.

Cepheus is home to some interesting deep space objects. NGC 188 is the closest open star cluster to the north celestial pole, and the Fireworks Galaxy (NGC 6946) is a spiral galaxy in which nine supernova have been observed, more than in any other galaxy. Also, a quasar that is powered by a supermassive black hole is among the most powerful objects in the universe is located in Cepheus.
http://en.wikipedia.org/wiki/Cepheus_(constellation)

IAU Cepheus chart, IAU and Sky & Telescope magazine (Roger Sinnott and Frick Fienberg), June 5, 2011.
IAU Cepheus chart, IAU and Sky & Telescope magazine (Roger Sinnott and Frick Fienberg), June 5, 2011.

© James R. Johnson, 2014.
jim@jrjohnson.net

Draco (The dragon)

Draco, Ursa MinorDraco is a large constellation of rather dim stars that is also one of the 48 constellations cataloged by 2nd century astronomer Ptolemy. Since it is a circumpolar constellation at 40 degrees north latitude, it is visible on any night at any time, but it reaches its highest nightfall ascension in January. Draco’s tail starts near the northernmost pointer star of the Big Dipper, and it roughly parallels the curvature of the Big Dipper handle before curving under the Little Dipper and turning back toward the south, and then terminating at the dragon’s head. The best chance of seeing this constellation will be under a very dark sky.

Thuban (Alpha Draconis), is the most interesting star in Draco. Six thousand years ago, when the Egyptian pyramids were build, Thuban was the Earth’s pole, or north star, and the Egyptians built north-facing entrances on the pyramids that were aligned to this star. Due to precession, the large circle that the Earth’s axis traces among the fixed stars every 26,000 years, Polaris has temporarily supplanted Thuban as the pole star. The most notable deep sky object in this constellation is the Cat’s Eye Nebula (NGC 4563).
http://en.wikipedia.org/wiki/Draco_(constellation)

IAU Draco Chart, IAU and Sky $ Telescope (Roger Sinnott and Rick Fienberg), June 5, 2011.
IAU Draco chart, IAU and Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), June 5, 2011.

© James R. Johnson, 2014.
jim@jrjohnson.net

Polaris (The North Star)

Circumpolar star trailsPolaris’ special significance is that it is the Pole Star, located very near the point at which the Earth’s northern axis intersects the celestial sphere. As a result of this unique location in the sky, Polaris will appear to remain stationary all night while all of the other stars will appear to rotate around it. You may have seen star trail images that illustrate this effect. Another implication of Polaris’ unique location is that it is a measure of one’s latitude. From Ashton, MD for example, Polaris appears 39.15° above the point on the horizon in the direction of due north, which corresponds to Ashton’s latitude on a map or globe. Polaris marks the end of the bear’s tail in Ursa Minor, or the end of the handle of the Little Dipper.

The best place to start when looking for Polaris is the Big Dipper which is part of the constellation known as Ursa Major. The two stars at the end of the bowl farthest from the handle are pointer stars. Follow an imaginary line from the pointer star at the  bottom of the bowl, through the one at the top of the bowl. The 2nd magnitude star that is about five times the distance between the two pointer stars is Polaris.

The Big Dipper Pointer Stars, Jim Johnson, December 27, 2014.
The Big Dipper Pointer Stars, Jim Johnson, December 27, 2014.

Polaris has not always been the Earth’s Pole Star, nor will it always be the pole star. As a result of the procession of the equinox, the axis about which the Earth rotates will trace out a large circle every 26,000 years, as illustrated below. This sounds like a long time, but when the Egyptian pyramids were built 5,000 years ago, Thuban in Draco was the pole star, and thus some north facing entrances of the pyramids were aligned on this star. In 8,000 years from now, Deneb in Cygnus will be the pole star, and the Earth’s axis will be aligned with a point near Vega in about 12,000 years from now.
http://en.wikipedia.org/wiki/Polaris.

© James R. Johnson, 2014.
jim@jrjohnson.net

Ursa Minor (The lesser bear)

320px-UrsaMinorCCSimilar to Ursa Major, which contains the Big Dipper asterism, Ursa Minor contains another recognizable asterism that is often called the Little Dipper. Some of the dimmer dipper stars can be difficult to locate in city skies, and the other stars forming the bear might be impossible to see. Polaris, the constellation’s brightest star, is found at the end of the bear’s tail, or at the end of the dipper handle. This star is thought by some to be significant because it is the brightest star in the sky, which is incorrect – Sirius in Canis Major is actually the brightest star in all of the night sky. An observer can verify that Polaris is not the brightest star in the sky by locating it, and comparing it with other stars in the rest of the sky. Polaris can be located by using the Big Dipper’s pointer stars, the two stars at the end of the dipper bowl away from the handle, and drawing an imaginary line upwards from the top of the bowl.

Ursa Minor is the 56th-largest constellation, and one of the 48 constellations cataloged by the 2nd century astronomer Ptolemy that remain among the 88 modern constellations. There are no Messier objects in this constellation.
http://en.wikipedia.org/wiki/Ursa_Minor_(constellation)

IAU Ursa Minor Chart, IAU and Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), June 5, 2011.

© James R. Johnson, 2014.
jim@jrjohnson.net

Ursa Major (The great bear)

Ursa MajorUrsa Major is a circumpolar constellation that was cataloged by 2nd century astronomer Ptolemy. The Big Dipper asterism is perhaps the most easily identifiable aspect of this constellation. As a circumpolar constellation at 40 degrees north latitude, it can be seen at any time on any clear night from a location with an unobstructed view of the northern horizon. In April, however, Ursa Major reaches its highest ascension at nightfall.

All seven stars comprising the Big Dipper were named by the ancients. The Big Dipper’s handle is the bear’s tail and the bowl is the bear’s hindquarter. Upon closer examination and in a darker sky, all of the constellations stars add to the dipper to form a distinct and complete bear. The two Big Dipper bowl stars opposite the handle are the pointer stars that guide the eye to Polaris, or the north star. Following the arc of the tail away from the bowl, a method sometimes referred to as “arc to Arcturus,” leads the observer to the star Arcturus in the constellation Bootes.  Starting at the end of the tail and moving around through the bottom of the dipper’s bowl, the are: Alkaid (Eta Ursae Majoris), Mizar (Zeta Ursae Majoris) and its naked eye binary companion star Alcor,  Alioth (Epsilon Ursae Majoris), Megrez (Delta Ursae Majoris), Phecda (Gamma Ursae Majoris), Merak (Beta Ursae Majoris), and Dubhe (Alpha Ursae Majoris) . Impress your friends by committing these stars’ names to memory and pointing them out on a late Spring evening when the dipper is high in the northern sky.

Ursa Major contains several Messier objects. A famous pair is M81, a nearly face-on spiral galaxy, and M82, a nearly edge-on galaxy, that gravitationally  interact with one another and can be see within a single field of view of a modest telescope. M101, 108 and 109 are three other Messier galaxies, and M97, a planetary nebula are also found in Ursa Major. One rather odd Messier object is M40, which is the only double star in the Messier catalog.
http://en.wikipedia.org/wiki/Ursa_Major_(constellation)

IAU Ursa Major chart, IAU and Sky & Telescope magazine (Roger Sinnott and Fick Fienberg), June 5, 2011.
IAU Ursa Major chart, IAU and Sky & Telescope magazine (Roger Sinnott and Fick Fienberg), June 5, 2011.

© James R. Johnson, 2014.
jim@jrjohnson.net