Post on 13-Jan-2016
Physics 101 AstronomyDay 2 notes
Ch. 1 -second half
The Zodiac and the seasons
Precession
Motion of the Moon
and eclipsesof Moon and Sun
Calendars
The Zodiac is the set of constellations that the Sun appears to go through during the course of one year.
• Right now, Aug. 27, 2015, at 2 p.m. the Sun is in Leo, although we can’t see the stars during the day.
• This can be seen on a sky chart if we set the time to sometime in the day, say 12 noon 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 2015 Month 8 Day 27 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.
• Compare with the zodiac chart in the previous slide. • At midnight, we could go outdoors and see Aquarius
high in the sky, opposite the Sun from Earth. (next slide)
• 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
• Notice that we see Aquarius high in the sky. • The sky chart also show us that the “Northern Cross”
officially known as Cygnus (“the swan”) is a constellation high in the sky at this time.
• For “homework” I would like you to go to this site: • http://www.globeatnight.org/ and use the magnitude
charts to see how much light pollution you have at your location. Try this between 8 and 10 p.m.
• http://www.globeatnight.org/magcharts/cygnus • This is a trial run, next week when the Moon is not in
the night sky you can do it again and give me your results for credit.
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 theastronomypicture 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
superimposedto 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 seenfrom 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, andSun 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 total eclipse of the Moon this fall, on Sept. 27-28, and you will be able to see the whole eclipse if the weather is clear.
• See: http://www.eclipsewise.com/lunar/LEnews/TLE2015Sep28/TLE2015Sep28.html
• We will schedule a viewing of this, and you can of course see it from other locations.
• 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. • Look at the Moon (not all weekend, though).