PHYS 1403 Stars and Galaxies Lunar Eclipse Wednesday (January 31 st ) Morning Super Moon so visible with naked eye Look in the western horizon Penumbral eclipse starts at 5:00 am Totality begins at 7:00 am low in the western horizon. By 7:25 am the moon will be below horizon Topics for Today s Class Chapter 2: Celestial Coordinate Systems Chapter 3: Lunar Cycles and Phases Chapter 3: Solar Day versus Sidereal Day Chapter 3: Moon s Sidereal Period Chapter 3: Moon s Synodic Period Chapter 3: Lunar Phases Vernal equinox is the intersection of the celestial equator and the ecliptic circle The equinoxes are equal day and night occur on March 21 st and September 22 nd. These are six months apart. Winter Solstice December 22 nd Summer Solstice June 22 nd Recap: Season Markers? Tilt of Sun s rays on a world map How do you locate county seat on a Texas map? June 22 nd : Sun s rays hit the directly on tropic of cancer December 22 nd : Sun s rays hit directly on tropic of capricorn pintrest.com 1
Celestial Coordinate Systems Astronomer use coordinate systems just like the one we use to describe the positon of cities on a map. We will study two different commonly use systems. Each have their advantage. Horizon Coordinate System Altitude (Alt) and Azimuth (Az) Depends on the Observers horizon lpc1.clpccd.cc.ca.us Source: www.nmm.ac.uk/tserver.php?f=altaz-star2.jpg... Equatorial Coordinate System Right Ascension (α or R.A.) Declination (δ or Dec.) Equatorial Coordinates are Universal. We already know how to find the celestial equator. So how do we find vernal Equinox How to find where the vernal equinox is on any date and time? 1.We know that the celestial equator culminates at 90- latitude from our south (90-32.2 = 57.8 degrees for Stephenville). 2.The angle between the two equinox is 180 degrees so 180 degrees = six months or 1 month = 30 degrees or 1 day = 1 degree (base on 30 day month for approximate calculations) 3.So if we compute how many days have elapsed from the last equinox, we can calculate approximately where the vernal equinox is on any date and time. 4.Computers can do these very precisely. Source: abyss.uoregon.edu/~js/ast121/lectures/lec03.html Chapter 3 The Cycles of the Moon 2
Sun on Meridian Sun on Meridian the next Day Solar Day Deneb on Meridian Time elapsed between two consecutive position of Sun on the Meridian 2017/01/27: 12:49:21 2017/01/28: 12:49:20 Difference 24 hours considering measurement error Deneb on Meridian the next Day Sidereal Day Time elapsed between two consecutive position of a star on the Meridian 2017/01/28: 12:43:16 2017/01/29: 12:38:39 Difference 4 minutes considering error in measurements Stars rise 4 minutes earlier each night Sidereal Day is 4 minutes shorter than Solar Day 3
Moon on Day 1 with reference to Aldebaran Moon after one Sidereal Period Moon s Sidereal Period Time elapsed between two consecutive position of Moon with reference to a Star 2017/02/03: 20:12:37 2017/03/02: 18:27:37 Difference 27.3 days New Moon with reference to Sun New Moon again after one Synodic Period 4
Moon s Synodic Period Time elapsed between two consecutive position of New Moon with reference to Sun 2017/01/28: 00:07:00 2017/02/26: 14:58:00 Difference 29.53 days The Phases of the Moon Why we see Phases of Moon From Earth, we see different portions of the Moon s surface lit by the sun, causing the phases of the Moon. Pbs.org Full Moon rising on date shown Moon rising the next day 5
Consecutive Moon Rise Time Difference 2017/01/12: 18:32:00 2017/01/13: 19:36:00 Moon rises one hour later every day We can use this information to estimate moon rise and moon set for any day The Phases of the Moon Evening Sky New Moon First Quarter Full Moon The Phases of the Moon Morning Sky Full Moon Third Quarter New Moon 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