It is important for observers to learn the constellations, because they help map the locations of the objects and events that are to be observed in the sky. The most frequently asked question that I get from the uninitiated person someone interested in star gazing, or locating a comet that has perhaps been in the news, is “where in the sky do I look?” This project, the centerpiece of Jim Johnson’s Astronomy, seeks to answer that question, and to provide additional information for stargazers wishing to gain a more sophisticated understanding of how the night sky works.
The Constellations Project can best be described by decomposing it into the four phases and describing those phases. I have also provided the status for each phase, and either links or instructions for accessing the content that has been developed in pursuit of the project.
Phase 1: Begin publishing a monthly newsletter written at a beginner to intermediate level to acquaint readers with what can be observed in the night sky each month. Status: Completed April 2014 by publishing the first edition of Scope Out Next Month. Every edition is available in the Scope Out Archive.
Phase 2: Write descriptive material for all of the constellations that an observer at a mid-latitudes of the northern hemisphere can see over the course of a year. Status: Completed December 2014. This content can be found by clicking on the Constellations category on the left menu, or by searching for a specific constellation using the search tool on the top menu bar.
Phase 3: Post articles that progresses from how to read a basic and static star chart to an understanding the dynamics of how the night sky moves over time, and how various solar system object move through the night sky. Status: Started in January 2015, and remains in progress. Expected articles are:
How to use Planetarium-type Applications on a Mobile Device
The Sun and the Ecliptic
The Movements and Phases of the Moon
The Movements of the Planets
Phase 4: Offer public speaking engagements to deliver talks based on the content developed in Phases 2 and 3. Status: Not started. Very anxious to get all of the pieces (Phases 1 through 3) in place so that I can begin Phase 4.
Please let me know if there is something that you would like to see in the project. Check back often to see my progress, or to see how the project might have morphed into something else.
When two Solar System objects arrive at their closest approach to one another as viewed from Earth, they are said to be in conjunction. This month I will examine the Moon’s close approaches to all five of the visible planets that were known to the ancients. As both the Moon and the planets are in constant motion, the actual conjunction is represented by an instant in time. Because of their slow apparent motion, the close approaches (visits?) can be observed for many hours before or after a conjunction.
As previously mentioned, the planets and the Moon never wander far from the ecliptic. One implication of this fact is that as the Moon completes its 28-day orbit around the Earth, it will be in conjunction with each of the planets once. This month, the young (thin) crescent Moon will first visit Jupiter near the western horizon in Gemini on May 3rd (closest) and 4th. Try to observe on both evenings and note that the Moon has moved eastward. Also note Jupiter’s position among Gemini’s stars, perhaps by making a sketch of Gemini that indicates Jupiter’s position. This sketch will come in handy near the end of the month.
Next up is a very interesting series of close encounters with three bright and colorful objects (Mars, Spica and Saturn) in the east at dusk on May 10th through the 14th. There are lots of things to observe over the course of these five evenings. First, the waxing gibbous Moon will grow larger each evening until it reaches full Moon on May 14th. Next, note that its location is a little farther east each evening. These two phenomena are the result of the Moon moving along its orbital path around the Earth, which changes its angle relative to the Sun. Also note that the point at which the Moon became full last month was closer to Mars (read about the lunar eclipse in April’s Scope Out), and this month the full Moon occurs closer to Saturn. This eastward slide of the full Moon from one month to the next happens because of the Earth moving along its orbital path around the Sun. And finally, note the distinct colors of the three objects: Mars is red, Spica is blue, and Saturn is yellow. The Moon will be near Mars on May 10th, and between Mars and Spica on May 11th. It will be between Spica and Saturn, but closer to Spica on the 12th, and closer to Saturn on the 13th. And finally it will be on the eastward side of Saturn on May 14th, the last evening of this string of encounters.
Another rewarding and challenging opportunity to observe the Moon arrives near month’s end as it transitions from a thin waning crescent in the eastern sky at morning, to a thin waxing crescent in the evening sky in the evening. First, observe the Moon as a thin waning crescent on the eastern horizon during its close encounter with Venus just before sunrise in the pre-dawn hours of May 25th. A careful observer might see an even thinner crescent very low on the horizon and closer to the sunrise point the next morning. After this, the Moon cannot be seen because it is lost in the Sun’s glare as it approaches new Moon (conjunction with the Sun) on May 28th. A young Moon (thin waxing crescent) emerges from the Sun’s glare on May 30th, and can be seen very low on the western horizon near Mercury. On the next evening, it will appear a little higher above the horizon, and it will once again visit Jupiter. Check the sketch that you made at the beginning of the Month. Has Jupiter moved among the stars since its last visit with the Moon on May 3rd and 4th?
Earth is predicted to pass through the path of Comet LINEAR on May 24th. LINEAR is a small comet that was discovered just a decade ago. It has a relatively short period, returning to the inner Solar System every five years, and travelling no farther away from the Sun than Jupiter. As a result of LINEAR’s orbit being perturbed during its last encounter with Jupiter, the path of its orbit now crosses the path of Earth’s orbit. Meteor showers occur when Earth crosses the orbital path of a comet, because stony debris are left behind as the icy comet evaporates when heated by the Sun. Since this is Earth’s first pass through this rather compact debris field, some astronomers are predicting a brief but spectacular meteor shower that begins at 2am on May 24th. Look for the peak, the highest number of meteors per hour, at around 3am, and the shower should subside by 4am. To observe, a darker sky is better because fainter meteors can be seen. The origin is near Usra Major’s ‘nose’, so watch a point about half way between the origin and the zenith (the point directly above your head). Be sure to dress warmly and sit in something comfortable, like a reclining lawn chair. http://sservi.nasa.gov/articles/comet-linear-to-produce-new-major-meteor-shower-in-2014/
Find The Whirlpool Galaxy (M51) by locating the three handle stars of the Big Dipper. Take a line from the middle star to the end of the handle. Now take a 90-degree turn toward the inside of the handle, just under half the distance between the two stars. Look for a small, diffuse fuzzy blob. Not impressive, even in a larger amateur telescope, but you will have observed your first galaxy! Images of the Whirlpool Galaxy in Wikipedia reveal that it is a spiral, face on galaxy. http://en.wikipedia.org/wiki/Whirlpool_Galaxy
The Beehive Cluster (M44), in Cancer was the first star cluster that I observed, and it left with me the impression of tiny diamonds on a black felt cloth. Interestingly, M44 is actually brighter than any of Cancer’s stars, but is difficult to see unaided in less than perfectly dark skies. The cluster is located in the center of the constellation, so locate it by looking half way between Pollux and Regulus. http://en.wikipedia.org/wiki/Beehive_Cluster
As Saturn cycles through its 29 1/2 year orbit about the Sun, we on Earth will alternatively see the top (north face) of Saturn’s rings for roughly half of its orbit, and the bottom half (south face) of Saturn’s rings for the other half. This occurs as a result of how the rings are inclined with respect to the plane of Saturn’s orbit. As the view transitions between upper and lower halves of the rings, our view will be edge on, and the rings will seem to have temporarily vanished. The last edge-on view was in 2009, at which time our current view of the north face of the rings began opening up. Even before Saturn’s rings fully open in 2017, our present view is pretty spectacular.
Polaris’ 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.
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.
Similar 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)
Ursa 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)
Cancer, the crab, is a zodiacal constellation of rather dim stars that can be difficult to see in light polluted skies. It is one of the 48 constellations cataloged by 2nd century astronomer Ptolemy. Cancer is located on the ecliptic, half way between Pollux in Gemini and Regulus in Leo, and is highest in the sky at nightfall in March. If Cancer’s stars are not visible, try using binoculars, and then look again once the various stars in the constellation have been located. Cancer is home to two Messier objects, M44 (the Beehive Cluster, or Praesepe) and M67. http://en.wikipedia.org/wiki/Cancer_(constellation)