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Home , Axial precession

Introduction to

Lecture 3: The -- System Moon Phases, , and

Elizabeth Charlton, 2015 1 The Sky from Earth

Elizabeth Charlton, 2015 2 The

• For objects such as the Sun and stars, we cannot directly perceive their distance • Historically the sky was perceived as a sphere with little lights on it

Earth within celestial sphere" by Tfr000 (talk) 20:06, 29 March 2012 (UTC) - Own work. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http:// commons.wikimedia.org/wiki/File:Earth_within_celestial_sphere.gif#mediaviewer/ File:Earth_within_celestial_sphere.gif

Elizabeth Charlton, 2015 3 The

• The apparent eastward path of the Sun throughout the – the plane of the

Earth’s orbit "Ecliptic with earth and sun animation" by Tfr000 (talk) 16:54, 15 March 2012 (UTC) - Own work. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http:// commons.wikimedia.org/wiki/File:Ecliptic_with_earth_and_sun_animation.gif#mediaviewer/ – tilted with respect to File:Ecliptic_with_earth_and_sun_animation.gif the due to the tilt of the Earth’s axis (23.5o)

Elizabeth Charlton, 2015 4 The ecliptic and the celestial sphere • – point where the ecliptic crosses the celestial equator • – point where the ecliptic and celestial equator are at the maximum 23.5o separation " orbit and ecliptic" by Tfr000 (talk) 01:59, 15 March 2012 (UTC) - Own work. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http:// commons.wikimedia.org/wiki/File:Earths_orbit_and_ecliptic.PNG#mediaviewer/ File:Earths_orbit_and_ecliptic.PNG

Elizabeth Charlton, 2015 5 Coordinates

• Just like the curved surface of the earth has a coordinate system …

• So does the sky, 2 systems in fact – Altitude and Azimuth – and

Elizabeth Charlton, 2015 6 Altitude-Azimuth Coordinates

• Also known as the Horizontal coordinate system – The observer’s local horizon is the fundamental plane separating the hemisphere’s – Altitude – or elevation. The angle between the object and the local horizon – Azimuth – the angle of the object around the horizon – Zenith – the point directly overhead – Zenith Distance – the distance from zenith

Elizabeth Charlton, 2015 7 Altitude-Azimuth Coordinates

"Azimuth-Altitude schematic" by TWCarlson - http://commons.wikimedia.org/wiki/ File:Azimut_altitude.svg. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Azimuth- Altitude_schematic.svg#mediaviewer/File:Azimuth-Altitude_schematic.svgElizabeth Charlton, 2015 8 Equatorial Coordinates

• Celestial Coordinate System – Analogous to the -Latitude Coordinate System on Earth – The projection of the Earth’s equator onto the Celestial Sphere is the fundamental plane (units: degrees arcsec arcmin) – Right Ascension – Measures the angular distance of an object eastward along the celestial equator from the vernal equinox (units: hr min sec) – Declination – Measures the angular distance of an object perpendicular to the celestial equator

Elizabeth Charlton, 2015 9 Equatorial Coordinates

"Ra and dec demo animation small" by Tfr000 (talk) 20:50, 17 April 2012 (UTC) - Own work. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http:// commons.wikimedia.org/wiki/File:Ra_and_dec_demo_animation_small.gif#mediaviewer/ File:Ra_and_dec_demo_animation_small.gif

Elizabeth Charlton, 2015 10 Cycles of the Sky

Elizabeth Charlton, 2015 11 of the Sun and Stars

• The observed motion of the Sun and Stars is due to the of the Earth – , revolution,

"AxialTiltObliquity" by Dna-webmaster - self-made by Dna- webmaster; earth-image from NASA. Licensed under Creative Commons Attribution 3.0 via Wikimedia Commons - http:// commons.wikimedia.org/wiki/ Elizabeth Charlton, 2015 12 File:AxialTiltObliquity.png#mediaviewer/File:AxialTiltObliquity.png Motion of the Sun

• Observing from the Earth, how does the Sun move? – Daily Motion – Yearly Motion

Copyright © James B. Kaler. All rights reserved. These contents are the property of the author and may not be reproduced in whole or in part without the author's express consent except in fair use for educational purposes. Thanks to reader number counter on blogger. Elizabeth Charlton, 2015 13 Motion of the Sun

• Daily Motion – What do we observe? – Due to the rotation of the Earth – – 86,400 SI (24 ) is the Astronomical unit of – Astronomical Definitions • Mean Solar Day – average time of a single rotation of the planet with respect to the Sun (average over the year = 24 hours) • Sidereal Day – an entire rotation of the planet with respect to the stars (3min 56sec shorter than solar day)

Elizabeth Charlton, 2015 14 Solar vs Sidereal Day

• Sidereal Day is shorter than the Solar Day

1 to 2 is one sidereal day

1 to 3 is one solar day

"Sidereal day (prograde)". Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Sidereal_day_(prograde).png#mediaviewer/ File:Sidereal_day_(prograde).png

Elizabeth Charlton, 2015 15 Motion of the Sun

• Yearly Motion – What do we observe? – Due to the revolution of the Earth – Year – A is defined as exactly 365.25 days of 86,400 SI seconds (24 hours). – Other Astronomical • – the time it takes the Earth to complete one revolution with respect to the (fixed frame of reference) • – the time it takes the Sun to return to the same position in the cycle of the seasons (for example: vernal equinox to vernal equinox)

Elizabeth Charlton, 2015 16 Keeping Time

• Using the position of the Sun or stars to keep time – Astrolabes –

"Iranian Astrolabe 14" by Jacopo Koushan (User:Jacopo188)Photograph by Masoud Safarniya "Equatorial topview" by WillowW - Own work. Licensed under Creative Commons (User:M.safarniya) - Own work. Licensed under Creative Commons Attribution-Share Alike 3.0 via Attribution 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Equatorial_sundial_topview.gif#mediaviewer/File:Equatorial_sundial_topview.gif File:Iranian_Astrolabe_14.jpg#mediaviewer/File:Iranian_Astrolabe_14.jpg Elizabeth Charlton, 2015 17 Keeping Time

• At local noon the sun is at its highest point in the sky (crosses the local meridian) • This is different for every longitude – Time Zones – Offset from

"Meridian on celestial sphere" by Tfr000 (talk) 16:56, 18 June 2012 (UTC) - Own work. Licensed under CC BY-SA 3.0 via "World Time Zones Map" by TimeZonesBoy - Own work. Licensed under Creative Commons Commons - https://commons.wikimedia.org/wiki/ Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Meridian_on_celestial_sphere.png#/media/ File:World_Time_Zones_Map.png#mediaviewer/File:World_Time_Zones_Map.pngElizabeth Charlton, 2015 File:Meridian_on_celestial_sphere.png 18 Motion of the Sun

• How does the motion of the sun depend on the time of year? • How does the motion of the sun depend on the location of the observer?

Elizabeth Charlton, 2015 19 Day Arcs

• At the equator – path during the

"Solstice-0" by Tauʻolunga - Own work. Licensed under Creative Commons Attribution-Share Alike 2.5 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Solstice-0.jpg#mediaviewer/File:Solstice-0.jpgElizabeth Charlton, 2015 20 Day Arcs

• At 20o latitude – path during the solstices

"Solstice-20" by Tauʻolunga - Own work. Licensed under Creative Commons Attribution-Share Alike 2.5 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Solstice-20.jpg#mediaviewer/File:Solstice-20.jpg Elizabeth Charlton, 2015 21 Day Arcs

• At 50o latitude – path during the solstices

"Solstice-50" by Tauʻolunga - Own work. Licensed under Creative Commons Attribution-Share Alike 2.5 via Wikimedia CommonsElizabeth - http://commons.wikimedia.org/wiki/ Charlton, 2015 22 File:Solstice-50.jpg#mediaviewer/File:Solstice-50.jpg Day Arcs

• At 70o latitude – path during the solstices

"Solstice-70" by Tauʻolunga - Own work. Licensed under Creative Commons Attribution-Share Alike 2.5 via Wikimedia Commons -Elizabeth http://commons.wikimedia.org/wiki/ Charlton, 2015 23 File:Solstice-70.jpg#mediaviewer/File:Solstice-70.jpg Day Arcs

• At 90o latitude – path during the solstices

"Solstice-90" by Tauʻolunga - Own work. Licensed under Creative Commons Attribution-Share Alike 2.5 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Solstice-90.jpg#mediaviewer/File:Solstice-90.jpgElizabeth Charlton, 2015 24 Precession

• Precession – change in the orientation of a rotating body – Axial precession of the Earth – movement of the rotational axis • Complete precessional cycle is 26,000 years or 1o every 72 years • Also called precession of the

"Earth precession" by NASA, Mysid - Vectorized by Mysid in Inkscape after a NASA Earth Observatory image in Milutin Milankovitch Precession.. Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Earth_precession.svg#mediaviewer/File:Earth_precession.svg Elizabeth Charlton, 2015 25 Precesssion

"Precession N" by Tauʻolunga - self, 4 bit GIF. Licensed under Creative Commons Attribution- Share Alike 2.5 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Precession_N.gif#mediaviewer/File:Precession_N.gif Elizabeth Charlton, 2015 26 Calendars

• A way of organizing time – periods are usually synchronized with the cycle of the Sun or Moon. • Calendars in use today: – Gregorian – – Hindu Calendars

" 1871-72" by Unknown - http://www.loc.gov/exhibits/world/images/s92.jpg Description: http://www.loc.gov/exhibits/world/world-object.html. Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/ Elizabeth Charlton, File:Hindu_calendar_1871-72.jpg#mediaviewer/File:Hindu_calendar_1871-72.jpg2015 27

• International Standard – refinement to the in 1582 by the Catholic Church – also reformed the used by the church – corrected the length of the year by .002% – brought the date of Easter to the correct time of year (agreed upon by the First Council of Nicaea in 325) • Leap years – a year containing an extra day to keep the calendar year synchronized with the astronomical or seasonal year – most years that are integer multiples of 4 are leap years – the years must be integer multiples of both 100 and 400

Elizabeth Charlton, 2015 28 Motion of the Stars

• – the apparent daily motion of stars around the celestial poles – due to the rotation of the Earth – visible stars depend on your location on the Earth and where the Earth is in its orbit

"Deep wide field with fog" by Naskies - Own workPreviously published: http:// www.iceinspace.com.au/forum/showthread.php?t=89854. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Deep_Crux_wide_field_with_fog.jpg#mediaviewer/File:Deep_Crux_wide_field_with_fog.jpgElizabeth Charlton, 2015 29 The Reasons For Seasons

What do you think?

Elizabeth Charlton, 2015 30 Hypothesis #1

• The energy put out by the sun changes over the year • Prediction: – The energy should be measurably different from space • Interpretation: – Hypothesis is wrong (energy doesn’t vary)

Elizabeth Charlton, 2015 31 Hypothesis #2

• The distance from the sun changes • Prediction: – The distance should be measurably different – It should be warmest when closest • Interpretation: – Hypothesis is wrong (coldest when closest)

Elizabeth Charlton, 2015 32 "Seasons1" by following Duoduoduo's advice, vector image: Gothika. - [1]. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http:// commons.wikimedia.org/wiki/File:Seasons1.svg#mediaviewer/File:Seasons1.svg Hypothesis #3

• The angle to the sun changes • Prediction: – The angle should be measurably different – It should be warmest when sun must direct – Seasons should be opposite in southern hemisphere • Interpretation: – Hypothesis is right

Elizabeth Charlton, 2015 34 "North season" by Tauʻolunga - Own work. Licensed under Creative Commons Zero, Public Domain Dedication via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:North_season.jpg#mediaviewer/File:North_season.jpg "Earth-lighting-summer-solstice EN". Licensed under Creative Commons Attribution-Share Alike 2.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Earth-lighting-summer- solstice_EN.png#mediaviewer/File:Earth-lighting-summer-solstice_EN.png "Earth-lighting-winter-solstice EN". Licensed under Creative Commons Attribution-Share Alike 2.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Earth-lighting-winter- solstice_EN.png#mediaviewer/File:Earth-lighting-winter-solstice_EN.png "Seasonearth". Licensed under Public domain via Wikimedia Commons - http:// commons.wikimedia.org/wiki/File:Seasonearth.png#mediaviewer/File:Seasonearth.png Phases of the Moon

! The appearance changes

! Amount of illumination ! Location of illumination

! What are the phases?

"Lunar libration with phase Oct 2007 450px" by Tomruen - Lunar_libration_with_phase_Oct_2007.gif. Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Lunar_libration_with_phase_Oct_2007_450px.gif#mediaviewer/ File:Lunar_libration_with_phase_Oct_2007_450px.gif

Elizabeth Charlton, 2015 39 Phases

! Name ! % illuminated

! New ! 0 % illuminated

! Crescent ! 0-50 % illuminated

! Quarter ! 50 % illuminated

! Gibbous ! 50-100 % illuminated

! Full ! 100 % illuminated

Elizabeth Charlton, 2015 40 Waxing verses Waning

! Waxing means

! % illuminated is increasing

! Waning means ! % illuminated is decreasing

Elizabeth Charlton, 2015 41 When is the Moon visible?

• The moon is not always up at the same time.

• The Moon rises roughly 50 later each day • Sometimes up at night • Sometimes up during the day

Elizabeth Charlton, 2015 42 Relative Positions

"Moon phases en" by Orion 8 - Own work. Licensed under CC BY-SA 3.0 via Commons - https:// commons.wikimedia.org/wiki/File:Moon_phases_en.jpg#/media/File:Moon_phases_en.jpg

Elizabeth Charlton, 2015 43 Tides

• What are tides? – The regular rise and fall of the water level surface • What causes tides? – The gravitational interaction between the Earth and Moon – The gravitation of the sun also contributes to

a smaller extent " schematic". Licensed under Public domain via Wikimedia Commons - http:// commons.wikimedia.org/wiki/File:Tide_schematic.svg#mediaviewer/File:Tide_schematic.svg

Elizabeth Charlton, 2015 44 "Tide overview" by iThe source code of this SVG is valid.This vector image was created with Inkscape. - Own work. 45 Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http:// Elizabeth Charlton, 2015 commons.wikimedia.org/wiki/File:Tide_overview.svg#mediaviewer/File:Tide_overview.svg Timing of tides

• How often is there a high tide? – Approximately every 12 hours • How often is there a low tide? – Approximately every 12 hours • Why do the of high and low tide change from day to day? – The moon is also orbiting around the Earth each

Elizabeth Charlton, 2015 46 Eclipses

• Two types of eclipses:

– Solar "Solar eclipse 1999 4 NR" by Luc Viatour - Own work www.lucnix.be. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Solar_eclipse_1999_4_NR.jpg#mediaviewer/ File:Solar_eclipse_1999_4_NR.jpg – Lunar

"Eclipse lune" by Luc Viatour - own work www.lucnix.beNikon case FE2 Otical refractor Vixen 1000mm F/D10addition of several images in Photoshop. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Eclipse_lune.jpg#mediaviewer/ 47 File:Eclipse_lune.jpg Elizabeth Charlton, 2015 Solar eclipse

! Definition…

! The shadow of the moon falls on the Earth

Elizabeth Charlton, 2015 48 Eclipse as seen from space

Elizabeth Charlton, 2015 Credit: Mir 27 Crew; Copyright: CNES 49 As seen from Earth

! Moon blocks out sun

Elizabeth Charlton, 2015 50 Solar Eclipse Geometry

! Where does the moon need to be compared to the earth and sun for a solar eclipse to happen?

! Moon is between Sun and Earth

! Possible at new moon phase

Elizabeth Charlton, 2015 51 Solar eclipse

"Geometry of a Total Solar Eclipse" by Sagredo - Own work. Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Geometry_of_a_Total_Solar_Eclipse.svg#mediaviewer/ File:Geometry_of_a_Total_Solar_Eclipse.svg 52 Elizabeth Charlton, 2015 Solar eclipse types

! Total solar eclipse ! Moon completely blocks Sun

! Partial solar eclipse

! Moon blocks part of Sun

! Annular solar eclipse

! Moon blocks center but not edge

Elizabeth Charlton, 2015 53 Visual Examples

! Definition ! Shadow of the earth falls on the moon

! Total lunar eclipse – ! moon entirely in Earth’s shadow ! Partial lunar eclipse – ! moon partially in Earth’s shadow

Elizabeth Charlton, 2015 55 Lunar Eclipse Geometry

! Where does the moon need to be compared to the earth and sun for a lunar eclipse to happen?

! Moon is behind earth compared to sun

! phase

Elizabeth Charlton, 2015 56 Lunar eclipse

"Geometry of a Lunar Eclipse" by Sagredo - Own work, images of Earth and Moon derived from NASA 57 Elizabeth Charlton, 2015 images. Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Geometry_of_a_Lunar_Eclipse.svg#mediaviewer/File:Geometry_of_a_Lunar_Eclipse.svg Why not every month?

• The Moon’s orbit is tilted with respect to the ecliptic: – Nodes – points where the Moon’s orbit crosses the ecliptic – Eclipses only occur when the Moon is

"Lunar eclipse diagram-en" by SuperManu - en:Image:Lunareclipsediagram2.gif by Tom Ruen, passing through a and derivating from Image:Solar eclipse fr.svg. Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Lunar_eclipse_diagram-en.svg#mediaviewer/ node File:Lunar_eclipse_diagram-en.svg

Elizabeth Charlton, 2015 58 Eclipse Calendar

• Eclipses in the UK – http://www.timeanddate.com/eclipse/in/uk/ oxford – Next solar eclipse visible from the UK: • Partial Solar Eclipse • 20 March 2015

• NASA Website ! http://eclipse.gsfc.nasa.gov/eclipse.html

Elizabeth Charlton, 2015 59