StarWatch: Moravian University Astronomy

SEPTEMBER 2023

SEPTEMBER STAR MAP | MOON PHASE CALENDAR | STARWATCH INDEX | NIGHT SKY NOTEBOOK

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Current Geomagnetic Field:

lunar phases

1411 September 3, 2023: Prepare NOW for the Partial Solar Eclipse of October 14: The US will be favored with two central solar eclipses in a period of just under six months. The first on October 14 will be an annular eclipse, where the moon will appear to have a ring of fire surrounding its disk. This event will favor Oregon, extreme northeastern California, Nevada, Utah, northeastern Arizona, New Mexico, and Texas. On April 8, 2024 the sun is completely hidden for about four minutes from Texas, southeastern Oklahoma, Arkansas, southern Illinois, Indiana, Ohio, northwestern Pennsylvania, New York, Vermont, New Hampshire, and Maine. Both of these events will be visible as partial solar eclipses from the Lehigh Valley if weather conditions permit. * Locally, from the Sky Deck of Moravian University, the October 14 partial solar eclipse begins at 12:05 p.m. EDT, reaches maximum obscuration of the sun's disk (25 percent) at 1:20 p.m. and ends at 2:36 p.m. The April 8, 2024 partial solar eclipse begins at 2:08 p.m. EDT. The moon covers the sun's disk to a maximum obscuration of 91.4 percent at 3:24 p.m. and leaves the solar disk by 4:35 p.m. These times for both eclipses do not vary by more than a minute or two for any location in southeastern PA. * For enthusiasts who wish to observe these two partial eclipses without optical aid, it is imperative to practice safe solar observing techniques. In its most simplistic form, this involves safely filtering the light of the sun before it reaches your eye. Not doing this properly could result in blindness. * To give an example of the sun's power, I looked at Sol with my unaided eyes on August 21, 2017 about 30 seconds before totality in the hopes of catching the beginning of the diamond ring phenomenon before I netted it on camera through my telescope. Although the sky was a deepening gray in color and the light of the sun illuminating the ground was ephemeral at best, I could not make out the disk of the moon and corona against the sky, just an incredibly, overwhelmingly bright, star-like object. I watched too early, was late in pulling off my solar filter, and totally missed the ingress diamond ring to my regret. * If 30 seconds before the start of totality, Sol remains too bright to catch any eclipse details, then the full disk of the sun is hundreds of thousands of times brighter. * The moral of this story is don't mess with the sun. Instead invest a few dollars and buy a couple of solar shades for you and your friends from a reputable company like Rainbow Symphony, https://www.rainbowsymphony.com/. See a photo of Eclipse Shades here. They market ISO (International Organization for Standardization) black Mylar eclipse glasses and eclipse viewers which produce a safe, comfortable image of the sun. Beware of less expensive and less reliable glasses and viewers from China and India that do not meet these high standards for eye safety. * As I write this article we are only 48 days away from the first E-day event, October 14. Eclipse shades take about 10 days to arrive by UPS, so this is not the time to delay if you want to view this partial solar eclipse safely from the Lehigh Valley. And don't throw them away after October 14. Store them safely in a plastic sandwich bag, and you'll be set for the partial phases of any solar eclipse during your lifetime. Ad Astra!

1412

September 10, 2023: Jupiter and Saturn in Opposition

My students are always aghast when they discover that my normal bedtime routine is in the 1-2 a.m. time frame. Then they become downright jealous when they discover that I like to get up between 9 a.m. and noon. This is because I have to be at my best for my evening classes, and it just doesn't make any sense to rise and shine with the sun. So when I pop out-of-doors after midnight to ensure that all is right with the cosmos, I receive a precursor of what is to come in most peoples' waking hours. Lately, I have been keeping an eye out for Saturn which is in the south at midnight and a rising celebrity in the east, Jupiter, which is absolutely impossible to miss because of its brilliance. * Saturn was in opposition to the sun two weeks ago, early on the morning of August 27 while Jupiter will be in the same configuration on November 3. What's the big deal about opposition? * As the planets revolve around Sol, they come into various named elongations or angular distances away from the sun as viewed from Earth. For a superior planet, a wanderer farther away from the sun than the Earth, these include elongations of 0 degrees or conjunction; 90 degrees, eastern and western quadrature, and 180 degrees from Sol which is referred to as opposition. The moon also goes through these same configurations which are its major named phases. An elongation of 0 degrees is a new moon when the moon and the sun are in the same direction, and Luna is not visible unless there is a solar eclipse. If quadrature occurs to the east of the sun, that's a first quarter moon visible in the evening. A western quadrature means that Luna is at last or third quarter, and will be seen to the west of the sun in the morning sky. At opposition the moon is full and visible all night long, the same for a superior planet in a similar configuration. After opposition the superior planet begins to favor the evening sky, rising earlier and earlier each day because the sun is gradually catching up to the wanderer. A superior planet's elongation decreases through eastern quadrature when it is visible in the south at sunset and finally to conjunction where it once again lines up with the sun. After the sun passes the planet in conjunction, the superior planet emerges into the morning sky headed for western quadrature when it is visible in the south before sunrise. The daily motion of the moon is much faster than the sun so it favors the evening sky before opposition and the morning heavens after a full moon. * For the inferior planets, Mercury and Venus, it is impossible for them to be opposite Earth, so angular distances away from the sun are at a maximum when the planet is at greatest eastern and greatest western elongations and forms a right angle with the Earth and the sun. At greatest eastern elongation, the planet has pulled farthest away from Sol toward the east and is visible in the western sky after sundown, very confusing to the uninitiated in astronomical jargon. Conversely, greatest western elongation allows these two inferior planets to be observed at their greatest angular distance from the sun in the morning sky before sunrise. * My wife said this blog was way too confusing, so simply get ready to see more of Saturn and Jupiter in the early evening sky in future months. A locator map for Jupiter and Saturn set for 10 p.m. can be found here. Ad Astra!

Jupiter and Saturn are well positioned to be observed by 10 p.m. in early September. Saturn can be found in the south, a bright star like object that does not twinkle in an area of the sky with few luminous stars except for lonely Fomalhaut below Saturn. The bright "star" in the east will be Jupiter.

1413 September 17, 2023: The Falling Time of Year: Similar to a total solar eclipse where an observer can witness two sunrises and two sunsets in a single day, this year I will have had the opportunity to participate in two fall seasons, the first in late April and early May, when I was in Australia where the seasons are opposite to the Northern Hemisphere and our upcoming autumn that will commence at 2:50 a.m., EDT on Saturday, September 23. * When I teach the transition times of the seasons, I note to my classes that March 21, June 21, September 21, and December 21 are good enough as a date since there is some variance from year to year. I also inform them that the autumnal and vernal equinoxes usually do not occur on the 21st. This curious fact is due to the Earth's elliptical orbit around the sun, bringing us closest to the sun in early January and farthest from Sol in early July. * When we are at perihelion, closest to the sun, Earth and the sun feel the greatest gravitational attraction for each other. This condition of closest distance causes the Earth's orbital speed to be at its greatest. Likewise, when Earth is at its maximum distance from the sun, aphelion, its orbital velocity is slowest. The change in distance of the Earth from the sun only varies by about three million miles, but that is enough to increase the amount of time by nine days that Earth lingers in the slower part of its orbit, between the vernal and autumnal equinoxes with summer's aphelion in between. The count was completed with whole days using the equinox dates for 2023. * Not only do the leaves fall in autumn, but the sun is also spiraling downward in its daily motion, causing the noontime altitude of the sun to decrease. On September 15, the sun's altitude at its highest point for the day in the Lehigh Valley was 52.5 degrees. Fast track to October 15, and 41 degrees will be the highest elevation the sun can attain for our locale. That's a drop of 11.5 degrees in just a month. Likewise, the time the sun is above the horizon also shrinks from 12 hours, 29 minutes to 11 hours, 10 minutes, a decrease of one hour and 19 minutes of daylight. No wonder I'm becoming depressed. * Traveling to Miami, Florida, the sun still drops in altitude by the same amount, 11.5 degrees, but because the largest city in the Sunshine State is 14 degrees farther south, the sun's altitude starts at 66.5 degrees on September 15. It drops to 55 degrees at high sun in the same length of time. Daytime shrinks by only 44 minutes. * Travel 13 degrees farther north to Dublin, Ireland. The sun is 13 degrees lower than the Lehigh Valley on September 15, starting at 39.5 degrees for high sun and dropping 11.5 degrees to 28 degrees by October 15. Twenty-six degrees is the noontime altitude of the sun in the Lehigh Valley at the winter solstice, the shortest day of the year. During that one month, the amount of daylight in Dublin will shrink by 2 hours and 4 minutes. Color me suicidal if I had to live there. Happy fall anyway to those who celebrate like my wife. Ad Astra!

1414 September 24, 2023: The Saros: The universe operates with a precision that must have left ancient Babylonian astronomers in awe, especially when they discovered the secret to predicting similar solar eclipses, perhaps as early as two millennia before the birth of Christ. The interval is 18 years, 9, 10, 11, or 12 days, depending upon the number of leap year days contained within that period. The Greeks dubbed it the saros, which means a significant quantity or measure, and indeed, it truly is a prodigious amount of time. If a total solar eclipse occurs today, in 6585 days, another total solar eclipse will happen in the same saros cycle. * Three sequences of time or drumbeats must be considered when understanding the saros. The governing pulse is the synodic period of the moon, the interval between successive new or full moons, 29.530588 mean solar days. A solar eclipse can only occur if the moon's phase is new. Luna needs to be located with precision between the Earth and the sun so that its near side is in darkness. A solar eclipse also cannot happen unless the moon is in or near the plane of the Earth's orbit because at least one of its two shadows, the narrowing cone of the umbra (primary shadow) or the expanding shadow cone of the penumbra (secondary shadow) must project towards and reach the Earth's surface. The moon's orbit is tilted to the plane of Earth's orbit by 5 degrees, 9 minutes, so an eclipse can only take place if the moon is at or near a crossing point, called a node, with the Earth's orbit. Two successive crossings of the same node, descending or ascending, occur every 27.212220 days. Finally, because the moon's orbit is an ellipse or oval, the moon must be at a similar distance from the Earth to facilitate the same type of eclipse: total, annular (ringed), or partial. The interim between the Earth's and the moon's sequential similar distances transpires every 27.554551 days and is called the anomalistic period. The saros or repetition of similar eclipses happens when all three intervals beat the same number of whole days. In other words, what whole number "X," when multiplied by the synodic period of 29.530588 days equals what different whole number "Y," when multiplied by the nodical period of 27.212220 days equals what different whole number "Z" when multiplied by the anomalistic period of 27.554551 days yields the same number of whole days. The number of days in 223 synodic months equals the same number of days in 242 nodical months and the same number of days in 239 anomalistic months, which equals 6585 days or 18 years 9, 10, 11, or 12 days. After the October 14 annular eclipse, the next ringed eclipse in that saros cycle will happen on October 24, 2041, 18 years, 10 days into the future. * Yes, there are leftover fractions that cause the location of the next eclipse to occur about one-third of the Earth's circumference to the west. These fractional differences also mean that saros cycles have a beginning and an end, starting as partial eclipses at either the north or south poles, then annular eclipses, sometimes hybrids (annular/total), total solar eclipses, and proceeding in reverse order until the saros cycle is complete, at the opposite pole. The Babylonians most likely discovered the saros cycle, the secret to predicting eclipses, from their extensive observations of the synodic or phase period of the moon. Ad Astra!