THE SOUTHWORTH PLANETARIUM 70 Falmouth Street Portland,Maine 04103 (207) 780-4249 usm.maine.edu/planet 43.6667° N 70.2667° W Altitude: 10 feet below sea level Founded January 1970 2021-2022: VIII "I have no special talent. I am only passionately curious." -Albert Einstein THE DAILY ASTRONOMER Monday, September 13, 2021 November's Micromoon Eclipse Part I: An Inconvenient Timing ____________________________________________ [image: penumbra.jpg] *Lunar eclipse*: the passage of the moon through Earth's shadow. Such eclipses can only occur when the moon is at opposition (full) _____________________________________________ So, we'll begin this brand new week with one of those fiendishly tricky, neuron-fraying philosophical conundrums. So, here goes. We're going to experience a nearly total lunar eclipse on November 19, 2021. As this eclipse will occur after midnight, we don't expect many people to join us at the Southworth Planetarium to observe it. See the tricky little problem? Well, if the lunar eclipse occurs on the 19th after midnight, does it actually occur on the night of November 18-19 or will it happen on the night of November 19-20? In the unforgiving realm of mathematical astronomy, such details tend to be important. There is nothing more soul-deflating than organizing a gathering to observe a celestial spectacle that ended 24 hours before. Well, we'll tell you. The eclipse occurs on the night of November 18- 19th. So, the actual eclipse will happen in the wee hours of November 19th. Before we proceed with the nuts, bolts, wires and grommets, we'll offer the following time-line, valid for Portland, ME but relatively close for the surrounding areas. *Friday, November 19th* - *1:02 a.m. Penumbral Eclipse begins. *If you wake up just for this part, you'll be sorely disappointed. The moon's brightness hardly diminishes at all when passing through the penumbra, or outer part of Earth's shadow. Apart from the satisfaction of knowing that you're witnessing a celestial event, the penumbral part will likely not offer much scintillation or inspiration. - *2:18 a.m. Umbral Eclipse begins. *Now the action starts! At 2:18 a.m, the moon makes contact with the umbra, defined as Earth's inner shadow. We can watch Earth's shadow arc migrating across the moon's face. Initially, it will appear as a fuzzy shade along the lunar limb. That shadow will soon become sharp and distinct. One can well understand why some ancient sky watchers ascribed an eclipse to a large black dragon devouring the moon. - *4:02 a.m. Maximum Eclipse *Another tricky aspect to this eclipse. It is not technically total, meaning that the entire moon isn't immersed in the umbra. Although this eclipse is partial, it's almost total. Let's look at a lovely graphic: [image: Lunar_eclipse_chart_close-2021Nov19 (1).png] Almost all of the moon will pass into Earth's umbra during the November 19th event. However, a small southern sliver won't. This partial eclipse will therefore look very much like a total lunar eclipse. - *5:47 a.m. Umbral Eclipse ends *After the moon reaches the maximum eclipse it will begin the slow move out of the umbra. At 5;47 a.m. the moon will only be immersed in the penumbra. As a penumbral eclipse hardly obscures the moon at all, the visual part of this eclipse is over. - *6:50 a.m. Moon set *Those observers who actually want to see the penumbral eclipse will have 1 hour and 3 minutes to do so. - *7:03 a.m. Penumbral Eclipse ends. *Nothing to see here. Of course, at this phase, there wasn't much to see, anyway. Note also the following solar time-line: - *5:00 a.m. Astronomical twilight begins *The Sun will be 18 degrees from the horizon at this moment. The first hints of atmospheric light scattering are visible. However, at 5:00 a.m. the sky will still appear quite dark. Light along the eastern horizon should first become noticeable around 5:10 - 5:15 a.m. - *5:34 a.m. Nautical twilight begins. * Nautical twilight begins when the Sun is 12 degrees below the horizon. Now the horizon becomes visible and only the brightest stars and planets remain in view. Incidentally, no planets will truly be visible at this time. Mars rises at 5:31 a.m., but as it will be only moderately bright and very low on the horizon, it will be exceedingly difficult to observe.* - *6:09 a.m. Civil twilight begins. *The sun will be six degrees below the horizon. Welcome to dawn! Only the moon remains visible and will look no different from any other moon, except it will be full and very close to the western horizon - *6:41 a.m. Sun rise* So, there you have it: a post midnight, nearly total, almost entirely visible micro-moon lunar eclipse...just like so many others. (And, yes, there have been thousands of them throughout our planet's history.) The "micromoon," incidentally, refers to the full moon that occurs when the moon is at or near apogee, the point at which the moon is at the greatest distance and so appears smaller than other full moons. This full moon is considered to be a micro-moon because apogee occurs on November 21st. While one will hardly notice the size difference, the micromoon is important because the moon moves more slowly when at apogee than it does when it is closer to Earth. As Kepler's second planetary motion law explains, a body close to the Sun moves faster than a more distant planet. The same principle applies to any body orbiting around another. So, this eclipse will last longer than it would have lasted had the moon been closer. Tomorrow, the Two Diagrams *Venus, Jupiter and Saturn will have all set the previous evening. Mercury will rise at 6:14 a.m., but won't be observable as it will appear during civil twilight. 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