Fall is in full swing, and darkness falls upon us early enough to accomplish some star gazing and still turn in at a reasonable hour. Also, the cooler days and evenings tend to produce more of those crisp nights with crystal clear skies, so please get out and enjoy the night sky during this almost perfect season.
There are four new constellations to introduce this month: another northern circumpolar constellation, two connected mid-latitude constellations and a zodiacal constellation. A planosphere or smartphone app like Google Sky Map can help determine where to look to find each constellation, and a Wikipedia link is provided to further aid in identifying each constellation’s appearance.
Cassiopeia (A Greek mythological queen)
This constellation is 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 circumpolar constellation that can be seen year round, it is found high above Polaris at this time of the year. 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.
Pegasus (A winged horse in Greek mythology)
This is a rather bright constellation that is nearly straight overhead at nightfall this month. Look for this constellation to the east, or left of, Cygnus. 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.
Andromeda (Cassiopeia’s daughter)
Although Andromeda is not a very distinct constellation in light-polluted skies, most of its stars can be observed. Locate this constellation by starting with the north eastern most start of the Great Square of Pegasus, and find the remaining stars flowing north east from there.
Aquarius (The Water Bearer)
This month’s zodiacal constellation is Aquarius. Locate this constellation by looking east, or left, of Capricornus and south (below) the Great Square of Pegasus. This is not a distinct or easy constellation, but some of its stars can be identified in suburban skies.
SOLAR SYSTEM OBJECTS
The Sun. Now that the autumnal equinox has occurred, the nights continue to get longer, and the days continue to get shorter, but at a slower rate. By month’s end, the sky will be dark enough to begin star gazing by 7:30pm! The Sun is situated below the celestial equator, which places it lower in the sky at noon. This lower position contributes to both shorter days and cooler weather.
|October 1||First Quarter|
|October 8||Full Moon/Lunar Eclipse|
|October 15||Last Quarter|
|October 17/18||Conjunction with Jupiter|
|October 23||New Moon/Solar Eclipse|
|October 27||Conjunction with Mars|
Mars is now in Sagittarius, and grows increasingly dim as it nears its greatest distance from Earth in its orbit about the Sun. Its distinct reddish color can still be seen, so be sure to get a glimpse of Mars just before total darkness arrives.
Jupiter remains a morning object, so be sure to look for it in the east if headed to work before sunrise. It continues to grow a little brighter and rise little earlier each morning as its separation from the Sun continues to increase.
DEEP SPACE OBJECTS (DSOs)
Andromeda Galaxy (M31)
This DSO 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!
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.
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.
© 2014 James R. Johnson.