Transcript day02
Physics 101 Astronomy Day 2 notes Ch. 1 second half The Zodiac and the seasons Precession Motion of the Moon and eclipses of Moon and Sun The Zodiac is the set of constellations that the Sun appears to go through during the course of one year. • Right now, Jan. 21, 2015, at 2:10 p.m. the Sun is in Capricornus, but we can’t see the stars in daylight. • This can be seen on a sky chart if we set the time to sometime in the day, say 2:10 p.m. using • http://www.heavens-above.com/skychart.aspx?lat=40.459&lng=90.672&loc=Macomb&alt=215&tz=CST • Note: you have to set the date and time to Year 2016 Month 1 Day 21 Hour 14 Minute 10 and click Update. You can also print black on white to save printer ink if you want to take a printed chart outdoors, having set the time to the evening hour when you plan to go out. • Compare with the zodiac chart in the previous slide. • At midnight, we could go outdoors and see Cancer high in the sky, opposite the Sun from Earth. (next slide) • You can try different months to see that the celestial sphere is in different orientations during the year. • Tonight at 11:55 p.m. the sky should look like this • http://www.heavens-above.com/skychart.aspx?lat=40.459&lng=-90.672&loc=Macomb&alt=215&tz=CST • Set the time for 23:55 and notice that we see Cancer and Gemini high in the sky. • The sky chart also show us that Orion is high in the sky at this time. Orion is easily seen during winter. • Also notice that if we go forward until about 6 a.m. we will see four planets along the ecliptic. • All five of the classical planets (the ones visible without a telescope), Mercury, Venus, Mars, Jupiter, and Saturn will be visible in the morning sky in another week or so. See this article in Sky and Telescope magazine: • http://www.skyandtelescope.com/astronomy-news/observingnews/get-up-early-see-five-planets-at-once-01182015/ The Ecliptic is the path of the Sun on the celestial sphere, which is tilted with respect to the celestial equator, due to the tilt of the Earth’s axis with respect to our orbit. The axis of the Earth is not perpendicular to the plane of the orbit of the Earth around the Sun. The Earth is tilted by 23.5o. Seasons are due to the changing orientation of the Earth and Sun, not because the Earth is orbiting closer or further from the Sun. Precession of a top • We can demonstrate a type of motion called “precession” by recalling the motion of a toy top (a wobbling motion). • A bicycle wheel can be used to demonstrate precession. • The Earth precesses because it is not a perfect sphere and because there are some forces on it from the Moon and planets. Precession of the Earth Precession of the Earth takes 26,000 years. The North Celestial Pole moves around a circle on the celestial sphere over long periods of time. Motion of the Moon and Phases of the Moon • The development of the current model of the solar system began with careful measurement of the movement of the Sun and the Moon. • To understand this, let’s review the motion and the phases of the Moon, as we currently understand them. • When we watch the Moon, it’s shape changes from one night to the next: From the astronomy picture of the day web site ( link ) Earth and Moon, separately From Apollo 17 spacecraft From Earth Earth and Moon, in one picture from the Galileo space probe as it traveled by the Earth on its way to Jupiter. Lunar Phases Lunar Eclipse (there are many good web resources) (link) Lunar Eclipse Solar Eclipse Solar Eclipse over China Solar Eclipse over Zambia sequence of photos superimposed to show the movement of the Sun Solar Eclipse over Antarctica Solar Eclipse – composite picture Solar Eclipse – composite picture (cropped) Solar Eclipse Types Penumbra and Umbra Classroom demonstration of umbra and penumbra • Use a large shop light, to get a uniform spherical source of light. • Then use a round (or even square) object and look at the shadow at various distances from source or screen. • (the next screen is black, in order to get a dark room for the demonstration). Shadow of Moon seen from Mir space station Animation of Moon eclipsing the Sun, as seen from inside the umbra. Animation of the view from the dark side of the Moon, looking down on the Earth during a solar eclipse. Eclipse geometry is favorable when the Earth, Moon, and Sun are lined up. This happens when the intersection of the orbital planes passes through the Sun. See below. Eclipse Tracks (also see NASA Eclipse page, Mr. Eclipse and Eclipser) A partial solar eclipse on Oct. 23, 2014 was visible in the US. • See this webpage (a pdf file): • http://eclipse.gsfc.nasa.gov/OH/OHfigures/OH2014-Fig04.pdf • Descriptions are on this page: • http://eclipse.gsfc.nasa.gov/OH/OH2014.html#SE2014Oct23P • Location data is given here: • http://eclipse.gsfc.nasa.gov/OH/OHtables/OH2014-Tab05.pdf Web page at NASA devoted to this eclipse (link) Example of a map of the eclipse path, showing the center line and boundaries of the region under the umbra (total) For the total eclipse of 29 March 2006 • There is an Atlas showing the path of totality for the total solar eclipse of 2017, from the mreclipse.com website. • See http://www.mreclipse.com/pubs/Atlas2017.html You can expect to see extensive coverage in the press, so you will definitely know this is coming up that summer. • There will be a penumbral (partial) eclipse of the Moon this spring, on March 23, and you will be able to see some of the eclipse if the weather is clear, although it will be visible from our location at moonset, not moonrise. • See: http://www.eclipsewise.com/oh/ec2016.html • More detail is at • http://www.eclipsewise.com/oh/oh-figures/ec2016-Fig02.pdf • Transits occur when a planet crosses between the Earth and the Sun, so we see a dark spot cross the Sun. This can only happen with Venus link or Mercury link. • Occultations occur when the Moon blocks out (occults) a planet. Link • For a discussion of year dates (BC, AD, BCE, and CE) see • http://eclipse.gsfc.nasa.gov/SEhelp/dates.html To do: • • • • • • • Get the textbook (access cards not needed). Finish Ch. 1. Start Ch. 2 ! Look at the syllabus and the dates. Mark your calendars for exam dates. First exam is exactly 2 weeks away! Welcome back to WIU. Enjoy the weekend.