1 Solar Eclipse 2017 Workshop IVayujeet Gokhale Truman State University
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3 Outline of Talk Some History Sun-Earth-Moon GeometryTidal Locking & Synchronous Rotation Phases of the Moon Lunar Eclipses Solar Eclipses
4 History: What have we learnt from Observing Solar Eclipses?The Sun has a REALLY hot corona! The surface temperature of the Sun is about 6000 K. The coronal temperature could be a million to 10 million K. How can gas so far away form the Sun’s core be this hot!? Test Einstein’s theory of General Relativity The Discovery of Helium Helium lines were first observed in the Sun’s spectra during the 1868 eclipse. The Solar Radius
5 The Sun, Earth, Moon System A Few QuestionsWhy does the same side of the Moon always face the Earth? Why does the Moon show phases? Why do we have Eclipses? What causes a Lunar Eclipse? What causes a Solar Eclipse?
6 Sun-Earth-Moon Geometry: BasicsThe Earth and Sun go around their common center of mass It takes one year to complete one orbit The Earth and Moon go around their common center of mass It takes about 27 days, 7 hours to complete one orbit but, It takes about 29 days, 12 hours from one full Moon to the next full Moon Somewhat incorrectly, we usually refer to these phenomena as: “The Earth goes around the Sun” and “The Moon goes around the Earth”, etc.
7 Geometric-Month & Phase-Monthearthsky.org
8 Tidal Locking & Synchronous RotationWhy does the same Side of Moon Face Earth?
9 Cosmic Coincidence!? The Sun’s diameter is ~400x the Moon’s diameter, but the Sun is also ~400x farther away from Earth!
10 Eclipses We know that the Moon is orbiting the Earth, the Earth is orbiting the Sun and both the Moon and the Earth are spinning about their own axes. We ask the question, why doesn’t the Moon block the Sun every month? Answer: The Moon’s orbital plane is tilted with respect to the ecliptic – the tilt is about 50. Eclipses can occur only if the Sun, the Moon and the Earth are all along the line of nodes.
11 Eclipses Why do we have Eclipses?Eclipses can occur only twice a year, since only twice during an year are the Sun, the Moon, and the Earth aligned along the line of nodes.
12 Eclipses Situation during most new moonsSituation during an Eclipse – occurs less often
13 Solar Eclipses
14 Solar Eclipses "John Beckman (United Kingdom) and other scientists use a Concorde supersonic passenger jet flying at 1,250 miles per hour (2,000 kilometers per hour) over Africa to extend the duration of solar eclipse totality to 74 minutes--10 times longer than can ever be observed from the ground“ (1973) Only the regions over which the umbra falls can experience the total solar eclipse, called “totality”. The umbra is only a few kilometers in size. And, since the Earth and the Moon are in motion, the duration of totality is only a few minutes – its never greater than 7.5 minutes! The umbra traces a path over the surface of the Earth, called the Eclipse path. Only the regions in the eclipse path will observe totality.
15 The Sun, Earth, Moon SystemWhy don’t eclipses occur on every New Moon day and every Full Moon day? Why don’t eclipses occur on the same days every year?
16 Orbit of the Moon: Eclipses do not occur on the same date and time every year.astronomynotes.com
17 Solar Eclipse 2017
18 Eclipse 2017 in Kirksville
19 Activities and Information HandoutsHow to make a pinhole camera How to build a sun-funnel: https://eclipse.aas.org/sites/eclipse.aas.org/files/Build-Sun-Funnel-v3.2.pdf
20 Activities and Information HandoutsAmerican Astronomical Society Eclipse Page: https://eclipse.aas.org/resources/educational-materials Night Sky Network (NASA-JPL): https://nightsky.jpl.nasa.gov/download-view.cfm?Doc_ID=588 NASA Eclipse 2017 Teacher Resource Page: https://eclipse2017.nasa.gov/k-12-formal-education NASA Museum Alliance Eclipse Page: https://informal.jpl.nasa.gov/museum/content/eclipse-2017 AAPT Eclipse Page:
21 Podcasts & Webinars https://www.nasa.gov/nasa-edge/1005-solar-eclipse-2017-preview-show https://eclipse.aas.org/resources/podcasts-webcasts https://www.youtube.com/playlist?list=PLo2YDpGbMTNBYH0jWAMunM4oaMJEpe0qf
22 “Eclipse” All that is now All that is gone All that's to come And everything under the Sun is in tune But the Sun is eclipsed by the moon. “There is no dark side of the moon really. Matter of fact it's all dark.”
23 Eclipse 2017 in Kirksville Extra Slides
24 History Eclipses have been the source of much fear, superstition, and also some scientific studies for centuries. Many cultures have mythological stories associated with eclipses – usually considered a ‘bad omen’ (crucifixion of Christ, wars & famine, etc.) The earlier reference to a solar eclipse seems to be from two Chinese astronomers in 2137 BCE, though these claims are somewhat dubious. Mesopotamian records from 1375 BCE mention an eclipse: “On the day of the new moon, in the month of Hiyar, the Sun was put to shame, and went down in the daytime, with Mars in attendance” https://eclipse.gsfc.nasa.gov/SEhistory/SEhistory.html
25 History
26 History In the ‘modern era’ one of the first scientifically significant comments about an eclipse comes from Kepler: “Johannes Kepler (Germany) is the first to comment scientifically on the solar corona, suggesting that it is light reflected from matter around the Sun (based on reports of eclipses; he never saw a total eclipse)" - Totality - Eclipses of the Sun (3rd ed) - Littmann, Espenak, and Willcox Edmond Halley also reported witnessing a solar eclipse in Soon after, in 1724 and 1733, observers recorded the presence of the Solar Corona and Solar prominences, which were later confirmed to be part of the Sun in 1842. https://eclipse.gsfc.nasa.gov/SEhistory/SEhistory.html
27 History The 1919 eclipse was especially important because it presented the first opportunity to definitively test Einstein’s theory of General Relativity. The proposition was that gravity affected light, space and time itself, and as a result the Sun would deflect starlight passing by it. Changes in the apparent direction of stars in the sky, seen close to the Sun during a total eclipse, could confirm the idea. Negative photo of the 1919 solar eclipse
28 The Sun, Earth, Moon SystemWhy does the same side of the Moon always face the Earth?
29 Tidal Locking & Synchronous RotationIn this figure, we stuck a white arrow into a fixed point on the Moon to keep track of its sides. If the Moon did not rotate as it orbited Earth, it would present all of its sides to our view; hence the white arrow would point directly toward Earth only in the bottom position on the diagram.
30 Tidal Locking & Synchronous RotationActually, the Moon rotates in the same period that it revolves, so we always see the same side (the white arrow keeps pointing to Earth).
31 The Phases of the Moon The differences in the Moon’s appearance from one night to the next are due to changing illumination by the Sun, not to its own rotation. Which side is light and which is dark changes as the Moon moves around Earth. “The back side” is dark just as often as “the front side” (say, on a Full Moon night). Since the Moon rotates, the Sun rises and sets on all sides of the Moon. With apologies to Pink Floyd, there is simply no permanent “Dark Side of the Moon.”
32 The Sun, Earth, Moon SystemWhy does the Moon show phases?
33 Moon Phase: The Sun, Earth, Moon System
34 The Sun, Earth, Moon SystemWhy do we have Eclipses? What causes a Lunar Eclipse? What causes a Solar Eclipse?
35 Lunar Eclipses A Lunar Eclipse occurs when the Sun, the Earth and the Moon are aligned along the line of nodes, in such a way that the Earth is between the Sun and the Moon, on a Full Moon’s day. A lunar eclipse may be total, partial or penumbral depending on the exact geometry of the alignment.
36 Lunar Eclipses Situation 1: Penumbral EclipseSituation 2: Total Eclipse Situation 3: Partial Eclipse
37 Solar Eclipses Not to scale © exploratorium.edu
38 Solar Eclipses A Solar eclipse occurs when the Sun, the Earth and the Moon are aligned along the line of nodes, and the Moon is between the Sun and the Earth on a New Moon’s day. A Solar eclipse may be total, partial or annular, depending on the exact geometry of the alignment of the Sun, Moon and Earth.
39 Solar Eclipses A partial Solar Eclipse astronomynotes.com
40 Annular Solar EclipsesAn annular Solar Eclipse astronomynotes.com
41 Solar Eclipses Only the regions over which the umbra falls can experience the total solar eclipse, called “totality”. The umbra is only a few kilometers in size. Moreover, since the Earth and the Moon are in motion, the duration of totality is only a few minutes – its never greater than 7.5 minutes! The umbra traces a path over the surface of the Earth, called the Eclipse path. Only the regions in the eclipse path will observe totality. astronomynotes.com
42 Solar Eclipses Remember that the Moon’s orbit is an ellipse and not a perfect circle. Thus, the Moon is sometimes closer to the Earth whilst at other times, it moves farther apart and at the opposite side of the orbit, it is at its farthest.