Physics 101 - Astronomy - Spring 2019

Class notes for day 3, Jan. 22, 2019

This third lecture covered the relationship between Earth, Moon, and Sun, and the topics of Phases of the Moon, and Eclipses.
In the OpenStax Astronomy book, see
section 4.5 pp. 120-124
section 4.7 pp. 129-135
Ch. 4 Key Terms p. 136
Ch. 4 Summary pp. 136-137

Auxiliary material for this section is found at (you will see some of the same ideas shown in your textbook, but with different figures): Motion of the Stars and the Sun and the next section Motion of the Earth. Look at these two web pages to reinforce your understanding of this material.

Phases and Motion of the Moon. We started with an animation of the phases of the Moon. See this Astronomy Picture of the Day for a multiple-photo display of a month's change in the Moon (unfortunately it runs too fast on newer computers). The size of the Moon appears to change a bit because the Moon's orbit is not a circle and it is somewhat closer to the Earth part of the month and so it appears larger. This is hard to see by eye, but it shows up in careful photography.

Figure 4-14 in the textbook shows details of the phases of the Moon. Look at Fig. 4-14 (p. 121) closely, it has a lot of information.  Section 4.7 has some graphics about eclipses, but look in my day03 powerpoint for more detail. I showed a picture of a lunar eclipse behind a lighthouse: http://apod.nasa.gov/apod/ap070310.html Here is a mosaic of the Moon at different times during an eclipse: http://apod.nasa.gov/apod/ap040506.html

Richard Pogge's website at Ohio State has his summary of his lecture on the Phases of the Moon but this contains more than I intend to cover in our course. (I asked him for permission to use some of his figures and to direct you to his website for more information.)

Solar Eclipses: I showed how to make an umbra and penumbra using a large light source and a round object (which should be smaller than the light source, just as the Moon is smaller than the Sun). I also showed a picture of the Moon's umbra over the Earth, as seen from the Mir space station. A version of that picture is here: http://apod.nasa.gov/apod/ap070610.html

Total solar eclipse over the Great Wall of China: http://apod.nasa.gov/apod/ap080831.html

Another picture taken in China (in 2008): http://apod.nasa.gov/apod/ap080805.html

Eclipse photo from Antarctica, with another photographer in the scene: http://apod.nasa.gov/apod/ap080504.html

The Sun's corona is seen in this composite photo of a total solar eclipse: http://apod.nasa.gov/apod/ap060407.html

Here is the NASA/GSFC Eclipse Home Page. Notice that this page has a list of upcoming events.

There is also a site with lots of pictures: McEclipse.com (this site may have commercial content, but it has a page on Lunar Eclipses for Beginners and a page on Solar Eclipses for Beginners which might be worth reading through if you have time.)

There was an annular eclipse of the Sun on Sept. 1, 2016 but it was not visible from here.
http://www.eclipsewise.com/solar/SEprime/2001-2100/SE2016Sep01Aprime.html 

There was a penumbral eclipse of the Moon on Feb. 11, 2017.
http://www.eclipsewise.com/lunar/LEprime/2001-2100/LE2017Feb11Nprime.html 

There was another annular solar eclipse on Feb. 26, 2017.
http://www.eclipsewise.com/oh/ec2017.html#SE2017Feb26A 

The big news in 2017 was a total eclipse of the Sun which passed over southern Illinois and other parts of the U.S. For a special page about the eclipse of Aug. 21, 2017 see http://www.eclipsewise.com/solar/SEnews/TSE2017/TSE2017.html

In addition to eclipses, there are similar celestial events called occultations and transits (which are very rare). A transit of Venus took place on June 8, 2004, and was seen in parts of North America. Another occurred on June 6, 2012. After that, no transit of Venus will occur until 2117. A transit of Mercury across the face of the Sun occured in 2016. A transit cannot be seen by eye, and of course you have to have a special filter for your telescope to block out most of the intense light of the Sun if you look at transits! Occultations are not hard to see but you have to know about the exact timing or you will miss them.

In addition to your textbook, for this lecture I suggest that you look at chapter 4 on Motion of the Moon from the Open Course: Introduction to Astronomy, which is available on the web and which you might want to read in addition to your textbook.

For a discussion of year dates (BC, AD, BCE, and CE) see

http://www.eclipsewise.com/help/dates.html

The first exam is on Thursday, Jan. 31. It will cover Ch. 1 - 4 along with any additional material in my powerpoints.