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: XXXVII "May you live every day of your life." -Jonathan Swift [image: preview-lightbox-does-santa-live-in-the-north-pole-550x550.jpg] THE DAILY ASTRONOMER Thursday, October 28, 2021 The North Pole Night That time of year has finally arrived: when we cross the vague demarcation separating the lush, fire-bright early autumn from the barren, ice coated pre-winter that inevitably follows it. Although we hearty folk can take solace from the assurance that vernal warmth will eventually soften winter's iron-hard soil, for now we are confronting the impending cold season. However, we are not going to allow ourselves to lapse into a despondent stupor because the world still remains stunningly beautiful and, besides, the higher latitudes have it worse. Today we focus our attention onto the ultimate in high latitudes: the North Pole. Why? To address an all too common astronomical misconception, namely: *The North Pole experiences six months of darkness.* Heavens above! One would think that such a protracted night could truly rip the kick and tickle out of Santa's jolly 'ol soul. Fortunately for St Nick, the North Pole's night isn't even half that long. To understand why the North Pole isn't steeped in deep shadow for half a year, we must remember the Sun's position relative to it and, most importantly, the life-sustaining atmosphere that envelopes our planet. Not only does the atmosphere supply us with so much free oxygen, it also scatters light. For instance, the sky doesn't go dark right after sunset. We experience three twilight phases between the sunset moment and the onset of true darkness: Civil twilight: when the Sun is between 0 - 6 degrees of the horizon. This is the time we generally regard as twilight: the sky exhibits a gorgeous display of colors and only the brightest planets and stars are visible. Nautical twilight: when the Sun is between 6 - 12 degrees of the horizon. During this phase, other stars appear while the horizon tremains visible. and Astronomical twilight: when the Sun is between 12 - 18 degrees of the horizon. At this third phase, the dimmer stars slowly come into view and the horizon vanishes. Once the Sun is more than 18 degrees from the horizon, any atmospheric light scattering will be negligible. Apart from the scattering, our pesky atmosphere also causes refraction, the "bending" of images away from their true positions. This effect is maximized at the horizon, where the atmosphere is at its thickest. Consequently, objects that are within half a degree of the horizon will still appear in our sky due to this refraction effect. On the autumnal equinox, the Sun remains in the sky at the North Pole, or , more precisely, an image of the Sun appears in the sky. Over a period of nearly 40 hours, the Sun turns around the sky and slowly sets. Civil twilight then lasts until October 8/9, when the Sun's angle first dips below six degrees. Imagine dusk lasting almost three straight weeks! Nautical twilight then begins and ends around October 24th. Although astronomical twilight commences and won't end until November 11/12th, the sky has already become quite dark. Technically,the North Pole Night begins around Veteran's Day, but one could still see a star-blazoned sky by late October. Astronomical twilight then begins at the North Pole on January 28th, when the ascending Sun comes to within 18 degrees of the horizon. The sky will still remain dark until around February 18th, when nautical twilight begins at the North Pole. The stars vanish and the sky brightens by late February. Civil twilight begins on March 5th and the first sliver of the Sun's upper limb protrudes above the horizon slightly less than two days before the vernal equinox. If Earth had no atmosphere, the North Pole would be plunged into darkness as soon as the Sun set. Daylight would only be restored on the vernal equinox when the Sun finally appeared above the horizon. However, Earth's airy blankets make life far more complicated. All the same, we are truly grateful for all the free oxygen. A brand new Halloween quiz tomorrow! To subscribe or unsubscribe from the Daily Astronomer: https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A= <https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A=1>