Lunar and Solar Eclipses of October 2014

Interestingly, there is both a lunar and a solar eclipse this month. The relationship between these events provides an opportunity gain a deeper understanding of eclipses, and it is an opportunity to explore some characteristics of the Moon’s orbit about the Earth.

Let’s start with the Sun’s role. The Sun’s path among the stars defines the ecliptic. The Sun’s location in the sky, and on the ecliptic can be computed rather precisely for any given date or time. The ecliptic can be found on most star charts. Note that the ecliptic becomes a full 360° circle when the left (west) and right (east) edges of a full sky chart are bent into a cylinder so that the two ends of the ecliptic meet.

A definition of Full and New Moon is essential to understanding solar and lunar eclipses. The Full Moon (the entire face of the Moon is lit) occurs when the Sun and Moon are opposite one another when seen from Earth. In other words, the Earth is located between the Sun and the Moon. The New Moon (none of the face of the Moon is lit) occurs when the Moon is located between the Sun and the Earth. The lit side of the Moon is facing the Sun, and the dark side is facing the Earth.

The Moon’s orbit is inclined to the ecliptic by about 5.5°, which means three things: 1) half of the Moon’s orbit is above the ecliptic, 2) half of the Moon’s orbit is below the ecliptic, and 3) the Moon crosses the ecliptic twice in each orbit. These two points are called nodes. The ascending marks the point at which the Moon crosses the ecliptic headed north, and the descending node marks the south-bound crossing. These nodes progress about the ecliptic once in about 18.6 years, which is why series of lunar and solar eclipses repeat ever 18.6 years.

If the Sun happens to be located at the point of the Moon’s crossing of the ecliptic at the time of the crossing, an eclipse will occur. Since the Sun’s disk (1/2° in diameter) occupies only about 1/720th of the 360° ecliptic, and the Moon may be as much as 5.5° above or below the ecliptic, an eclipse is a rather rare event.

A lunar eclipse occurs when the full Moon passes through the Earth’s shadow. Given that the Earth is between the Sun and Moon at Full Moon, it stands to reason that the Earth’s shadow will fall upon the Moon, if the full Moon happens to be crossing the ecliptic.

A solar eclipse occurs when the new Moon casts its shadow upon the Earth’s surface. This stands to reason given that at New Moon, the Moon is located between the Sun and the Earth. To an observer at a fixed location on the surface of the Earth, the Moon’s dark disk is seen to move across the Sun’s face, either partially, or fully blocking out the Sun at the eclipse’s maximum.

October 8th – Total Lunar Eclipse
This eclipse will begin when the Moon enters the prenumbra (lightest part of the Earth’s shadow) at 4:45am. The Moon enters the umbra (the darkest part of the Earth’s shadow) at 5:15am, and Moon is fully within the umbra (total eclipse) at 6:25am. Unfortunately, the Sun rises and the Moon sets before the eclipse ends.
http://en.wikipedia.org/wiki/Lunar_eclipse

October 23rd – Partial Solar Eclipse
This month’s solar eclipse is “partial,” because the Moon’s dark disk will not fully cover the face of the Sun. The eclipse will begin when the Moon first begins to cover the Sun’s face at 5:52pm, and it will reach its maximum coverage of the Sun’s face at 6:17pm, which is sunset.
http://en.wikipedia.org/wiki/Solar_eclipse

Andromeda Galaxy (M31)

M31boboThe Andromeda Galaxy is the Milky Way’s closest galactic neighbor. At 2.5 million light years away, it is rather large, spanning about 3° of the sky (about the width of six full Moons), and can be seen with the unaided eye when viewed under clear dark skies. As opposed to dramatic spiral arms that appear in photographs, M31 appears as a fuzzy blob of light, which is actually the Andromeda Galaxy’s core, when viewed with binoculars or a modest telescope. Consult a start chart to locate this object in the Andromeda constellation. If you do happen to view this object under a clear, dark sky, and without optical aid, then the answer to “how far can I see?” becomes 2.5 million light years!
http://en.wikipedia.org/wiki/Andromeda_Galaxy

 

Aquarius (The water bearer)

Constellation AquariusAquarius, the water bearer, is a rather dim and nondescript zodiacal constellation. This southern constellation was cataloged by 2nd century astronomer Ptolemy. It is located in a region known to  the ancients as “the sea” because several water constellations, to include Capricornus (the sea goat), Piscis Austrinis (the fish), Pisces (the fishes), and Cetus (the sea monster) are gathered there. It is situated on the ecliptic between Capricornus and Pisces, and is just south of the Great Square of Pegasus. Aquarius reaches its highest nightfall ascension in November. Three globular star clusters, M2, M72 and M73 are the only Messier objects found in this constellation. The Eta Aquariids is the strongest meteor shower radiating from Aquarius, peaking at about 35 meteors per hour between May 5th and 6th.
http://en.wikipedia.org/wiki/Aquarius_(constellation)

IAU Aquarius chart, Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), January 27, 1997.
IAU Aquarius chart, Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), January 27, 1997.

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

Andromeda (Cassiopeia’s daughter)

Andromeda, CassiopeiaAndromeda, the mythological daughter of Cepheus and Cassiopeia, is located near these two constellations and among several other constellations representing the Perseus myth, to include Perseus, Pegasus, and Cetus. It is one of the 48 constellations cataloged by 2nd century astronomer Ptolemy that remain among the 88 modern constellations. It is found directly overhead at the zenith after sunset in December. Although Andromeda is not a very distinct constellation in light-polluted skies, most of its stars can be observed. It’s brightest star, Alpheratz (Alpha Andromeda), is shared with the constellation Pegasus, and marks one corner of the Great Square of Pegasus. Locate this constellation by starting with the north eastern most star of the Great Square of Pegasus, and find the remaining stars flowing north east from there.

The Andromeda Galaxy (M31), M31boboThe Milky Way’s closest galactic neighbor, is found in this constellation. M31 can be found with the unaided eye in the very darkest of dark skies, but can easily be found with a binocular or telescope under most adverse light pollution conditions. M31 and M110 are two of M31’s dwarf companion galaxies that can also be seen in most photographs of M31.
http://en.wikipedia.org/wiki/Andromeda_(constellation)

IAU Andromeda chart, IAU and Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), June 4, 2011.
IAU Andromeda chart, IAU and Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), June 4, 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