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W:09/19/18 Eclipses PHYS 1411 Intro to Astronomy Extra Credit Homework Announcement Assigned on MindTap for Chapter 1, 2, 3 Due Monday December 3rd , 2018 @ 5:00 am Topics for Today’s Class Topics for Today’s Class • Chapter 3: Lunar Eclipse • Chapter 3: Solar eclipse – How to make a shadow or an eclipse? – What is a Solar eclipse? – Types of shadows – How to safely observe Solar eclipse – The importance of angular diameter in – Types of Solar eclipse eclipses – Some examples and dates – What is a Lunar eclipse? – Conditions for Solar and Lunar eclipses to – Types of Lunar eclipses occur – Why Pinkish Moon during Lunar eclipse? – Saros Cycle The Angular Diameters of the How to make a shadow? Sun & Moon • The shadow cast by a map tack can be used to understand how shadows produce eclipses – Umbra = The region of total shadow – Penumbra = The region of partial shadow – Penumbra = The region of partial shadow 1 Angular Size and Distance Two Types of Movements Increasing Distance from Eye Dime Quarter Partial Total Annular Not Visible Transit Occultation View from Eye View from Eye What is a Lunar Eclipse? Small Angle Formula Earth’s shadow consists of a zone of partial angular diameter linear diameter shadow, the Penumbra, 206,265 distance and a zone of full shadow, Example for Moon the Umbra. angular diameter 3476 km 206,26 5 384,000 km 1870 angular diameter 187 0 0.5 60 60 If the moon passes through Earth’s full shadow (Umbra), we see a lunar eclipse. If the entire surface of the moon enters Angular Diameter of Sun and Moon is important for Eclipses to occur the Umbra, the lunar eclipse is total. Types of Lunar Eclipses A Total Lunar Eclipse (1) • The Moon’s orbit is inclined by a bit more than 5º relative to Earth’s orbital plane – Moon does not always pass through center of the Umbra • Total lunar eclipse – All of Moon enters the umbra • Partial lunar eclipse – Some part of the moon is in Umbra – Rest of the Moon enters the penumbra • Penumbral lunar eclipse – Moon only enters the penumbra – Moon is only partially dimmed 2 A Total Lunar Eclipse (2) Lunar Eclipses: 2002-2012 A total lunar eclipse can last up to 1 hour and 40 min. Typically, 1 or During a total 2 lunar eclipse, the eclipses per moon has a year. faint, red glow, reflecting sun light scattered in Earth’s atmosphere. What is a Solar Eclipses? Observing an Eclipse The sun appears approx. as large in the sky (same angular diameter ~ 0.50) as the moon. When the moon passes in front of the sun, the moon can cover the sun completely, causing a total solar eclipse. The Moon’s Shadow: A Total Solar Eclipse Solar Eclipses: 2002-2012 Approximately 1-2 total solar eclipse per year (a) The umbra of the Moon’s shadow sweeps from west to east across Earth, and observers in the path of totality see a total solar eclipse. Those outside the umbra but inside the penumbra see a partial eclipse. (b) Eight photos made by a weather satellite have been combined to show the Moon’s shadow moving across the eastern Pacific, Mexico, Central America, and Brazil during an eclipse in 1991. 3 Total Solar Eclipse August 2017 Solar Eclipse in US Chromosphere and Corona https://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html Prominences NASA Solar Atmosphere Revealed Diamond Ring Effect Earth and Moon’s Orbits Are Ecliptic Orbit cause Annular Eclipse Slightly Elliptical When Earth is near perihelion, and Apogee = the moon is near apogee, we see position furthest an annular solar eclipse. away from Earth Perihelion = position Earth closest to the sun Moon Perigee = position closest to Earth The angular Sun sizes of the moon and the Aphelion sun vary, (Eccentricities greatly exaggerated!) Perigee = position Apogee Perihelion Aphelion depending on furthest their distance away from Earth. from the sun 4 Annular Solar Eclipses (2) Predicting Eclipses • Astronomers in early civilizations could make educated guesses as to which full moons and which new moons might result in eclipses • Making exact eclipse predictions requires a computer and proper software • Today we can predict precise date and time of all eclipses Almost total, annular eclipse of May 30, 1984 Lunar Node Conditions for Eclipses The moon’s orbit is inclined against the ecliptic by ~ 50. Eclipses occur only near lunar nodes A points where the lunar orbit intersects the ecliptic is called a node. Ecliptic A solar eclipse can only A lunar eclipse can only occur if the moon passes a occur if the moon passes a node near new moon. node near full moon. Wikipedia Conditions for Eclipses Saros (Eclipse) Cycle Line of Nodes has to point towards the Sun • The Eclipse cycle is a period of 18 years, 11 days and 8 hours (6585.321 days or 223 lunar months) • From the first eclipse of the year the line of nodes slips westward 19.4 degrees per year. Causing the eclipse season to begin 19 days earlier every year. Eclipses occur in a cyclic pattern. 5 Saros Cycle Saros Cycle After 3 Saros cycles (54 years 1 month). The eclipse cycle occurs in the same part of the earth www.astronomy.com Solar and Lunar Eclipse First Term Project https://www.youtube.com/watch?v=kgbK2FZFFdw • Making and Using a Cross-staff – Handout with Details will be on class web page later this week (Friday 21st September) https://www.youtube.com/watch?v=is8OLhGgLAE – Due: October 29th 2018 End of Class hour – Let’s talk about the construction today Acknowledgment • The slides in this lecture is for Tarleton: PHYS1411/PHYS1403 class use only • Images and text material have been borrowed from various sources with appropriate citations in the slides, including PowerPoint slides from Seeds/Backman text that has been adopted for class. 6.
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