Motion of the Moon Moon shines not by its own light but by reflected light of Sun  Origin of the phases of the moon Moon revolves around the Earth period of revolution = 1 month

Phases of the Moon

Phases of the Moon (cont’d) Moon rotates around earth in one month Moon rotates around itself in the same time  always shows us the same side!  “dark side of the moon” (not dark at all!)

Eclipses One celestial object hidden by other or in the shadow of another Solar eclipse: sun hidden by the moon Lunar eclipse: moon in earth’s shadow (sun hidden from moon by earth) Also: eclipses of Jupiter’s moons, etc. Most spectacular because moon and sun appear to be the same size from earth

Solar Eclipses Umbra – region of total shadow Penumbra – region of partial shadow Totality lasts only a few minutes! Why isn’t there a solar eclipse every month?

Solar Corona

Annular Eclipse 1 3 2

Lunar Eclipses Moon moves into earth’s shadow… …and out of it (takes hours!)

Question Why isn’t there an eclipse every month ?

Skylab Workshop Choose one of six possible projects –All involve observing May work in groups of up to four Hand in one report per group Due Tuesday, March 11 (strict deadline!) Weather may be a problem, so start early! –If you wait and the weather turns bad, you will have to do the term paper Come ask me if you have questions

Writing a Report Introduction Procedure –Describe what you did –Give enough detail so that others could repeat your measurements Presentation of data –Tables or graphs may be helpful –Include description, units, etc. – not just numbers Answers to any questions Conclusions

Writing a Report At least one paragraph per section, except for questions About 2–4 pages total Properly cite any references (articles, books, etc.) that you use –See e.g. the Blair Handbook or other writing guide for acceptable formats Strive for clarity – the point is to communicate!

Making Measurements Errors –Random –Systematic With every measurement, it is essential to provide an estimate of the uncertainty – the likely range of errors Example: –Using a ruler marked in mm, we round to the nearest marking – at most off by half a division, or 0.5 mm –Cite a measurement of 15 mm as 15  0.5 mm to indicate that the real value of the length is likely to be anywhere between 14.5 mm and 15.5 mm –If a theory predicts a value of 15.2 mm, then a reading of 15  0.5 mm is in agreement with the theory but a reading of 15  0.1 mm is probably not

#1: Now where was I? Determining the difference between the solar and sidereal days –Understand the difference before you start Measure interval between times when a star returns to the same spot on the sky Measure times as accurately as possible (you should be able to get to within a second or so) Need 4–6 measurements, best if spread out with a few days between each measurement Ask if you have questions about the error analysis!

#2: Road Trip Measure the size of the Earth using Eratosthenes’s method Probably the most math of any of the projects (some trig) Need two sets of measurements separated (N–S) by 150 miles or so –Detroit or Lexington, say –Don’t go too far East or West (a little is okay) Shadow Gnommon To Sun

#2: Road Trip (cont’d) Need two sets of measurements separated (N–S) by 150 miles or so –Detroit or Lexington, say –Don’t go too far East or West (a little is okay) Measurements should be as close as possible in time –Ideal would be on the same day by different group members Ask me if you want more details on the trig, or if you have questions about the error analysis Shadow Gnommon To Sun

#3: Where did I put that chart? Study variation of the rising/setting points of the sun over time Need at least 10 sunrises or sunsets; more is better Measure time and azimuth (angle relative to North) –Note position of sunrise/sunset on horizon –Measure angle to that position relative to some fixed landmark (mountain, etc.)

#4: That thing is supposed to be a bear? Study the apparent motion of the stars in the night sky Requires one entire (clear) night Most involved equipment making of all the projects! Best to get out of the city; avoid bright moon Every hour, measure elevations of four stars in different constellations using a quadrant

#5 Take a Photo! take long exposure photographs of the night sky. stars appear to rotate once around the Earth in a day measure the duration of one rotation, this is the duration of a sidereal day Need camera capable of making long exposure photos and tripod to mount the camera absolutely stable. Time required: About an hour for a couple of nights which do not have to be adjacent. What to do: take photos of the night sky centered around the north pole star, Polaris. The stars will establish part of an arc around Polaris on the photo.

#6 Simulated Experiments In case weather becomes an issue Download manual and executable file from webpage Two choices: –Jupiter’s Moons –Hubble Law

Development of the Scientific Method

The Scientific Method Systematized by Francis Bacon, Descartes and Galileo in the 17 th century Not the only way of knowing, but a very successful one A method to yield conclusions that are independent of the individual Conclusions are based on observation

Francis Bacon ( ) Contemporary of Shakespeare, Elizabeth I, Kepler and Galilei Rejects Aristotelianism and Scholasticism Major Work: Novum Organum (1620) (“New Tools”, the old Organum was Aristotle’s)

Francis Bacon ( ) Novum Organum Title: Allegory on the daring mind: A Ship passes through the “pillars of Hercules”, beyond old knowledge.

Rene Descartes – The Rationalist Described the method to do science, known for his mind-body dualism Major Works: Discourse (1637) [full title: Discours de la méthode pour bien conduire sa raison et chercher la vérité dans les sciences] Meditations on first Philosophy (1641) [6 Meditations: Of the Things that we may doubt; Of the Nature of the Human Mind; Of God: that He exists; Of Truth and Error; Of the Essence of Material Things; Of the Existence of Material Things; Of the Real Distinction between the Mind and the Body of Man] Rene Descartes ( )

Rene Descartes’ Discourse Describes the method to do science in a straightforward way (see below) Major points: Science must be based on correct reasoning (logic) Science must be formulated in mathematical language Starting line: “Good sense is the most evenly distributed thing in the world, for all people suppose themselves so well provided with it that even those who are the most difficult to satisfy in every other respect never seem to desire more than they have.”

A Classical Example Aristotle observes that during lunar eclipses the Earth’s shadow on the moon is curved He assumes it will be curved for all eclipses A hypothesis that explains this: the earth is round A prediction of this theory is that the location of the stars in the sky should be different for observers at different latitudes This is confirmed by additional observations –E.g. Canopus is visible in Egypt but not further north

Scientific Literacy An important skill to have in an increasingly complex society As a voting citizen you should know what you are voting on As a consumer you should know (or be able to figure out) what you buy Makes life more interesting Nobody knows everything, but smart people can figure out fast if something is obviously wrong