Download Lecture slides on The Moon’s Orbits is Titled | ASTRO 120 and more Assignments Astronomy in PDF only on Docsity! Astro 120 Fall 2003: Lecture 6 page 1 • The Phases of the Moon • new->waxing->1st Q->Full->waning->3rd Q-> new • where in the sky can you find a _______ moon? • lunar rotation - once per month - keeps the same face pointing towards Earth • The Moon’s Orbit • tilted 5o to the ecliptic • intersects ecliptic at two nodes (ascen’g, descen’g) • eclipses possible only when moon is at a node Brief review of last time: The Phases of the Moon Reading: Bennett, Chapter 2, Section 2.6 Chapter 3, Sections 3.1-3.5 Help Room: Now Open - Schedule on website Mars Viewing: McFarland Park, Saturdays in September Problem Set #1: Available NOW on the Astro 120 Website; Due 9/12-15 Print from your browser! Astro 120 Fall 2003: Lecture 5 page 2 The Moon’s Orbit is Tilted! why not ECLIPSES every new and full moon? The Moon’s orbit is tilted 5o to the ecliptic 23.5 ecliptic Nodes: crossing points of lunar orbit with ecliptic Line of Nodes: connects lunar nodes Astro 120 Fall 2003: Lecture 6 page 3 Need the Sun to lie at a node at new or full moon for an eclipse to occur Astro 120 Fall 2003: Lecture 5 page 4 Regression of the line of nodes: Line of nodes circles WESTWARDS in 18.7 years: Highest/Lowest Moon 9.35 years later: smallest lunar altitude variation ad da Astro 120 Fall 2003: Lecture 6 page 5 Earth and Moon Shadows • The UMBRA - region of total obscuration of Sun • narrow, cone-shaped • finite length • The PENUMBRA - region of partial obscuration of sun • broadening cone-shaped • “infinite” length umbra penumbra moon or Earth Astro 120 Fall 2003: Lecture 6 page 6 • Moon passes through Earth’s shadow • total • partial • penumbral • visible whenever the moon is above horizon • duration up to 1.5 hours (total) and 3 hours (partial) Circumstances of a Lunar Eclipse Earth’s umbra penumbra view from Earth Earth’s shadow at Moon’s distance Moon’s path Partial Total Penumbral Astro 120 Fall 2003: Lecture 6 page 7 • Moon’s shadow crosses Earth’s surface • total, partial, annular • Moon’s umbra’s length almost = average Earth-Moon distance • Moon and Sun have ~ same angular size • so Sun may be fully covered – a total eclipse • or Sun may be partially covered - a partial eclipse • or moon may be too far away – an annular eclipse Circumstances of a Solar Eclipse Astro 120 Fall 2003: Lecture 6 page 8 • partial phases (Moon’s penumbra) widely viewable • Moon’s umbra sweeps a narrow path across Earth • 0 to 200 km across • up to 10,000 km long • sweeps across Earth at 3400 km/h ! • TOTALITY visible only from the “eclipse track” • duration of totality - usually 2-3 min (but up to 7 min) A Total Solar Eclipse umbra penumbra moon Sun Earth Umbra
