AST 115 1st Edition Lecture 5 Outline of Last Lecture I. Measuring time continuedII. Calendarsa. Types of calendarsIII. PrecessionIV. Introduction to eclipsesOutline of Current Lecture I. Eclipses continueda. Solar eclipsesb. Lunar eclipsesII. Measuring anglesa. Small angle equationCurrent Lecture Eclipses continued:o There must be at least 4 eclipses of all kinds that occur during any calendar year, but as many as 7 can occur.o 3 types of solar eclipses:- Total (rare) The Moon completely covers the Sun- Partial Moon’s umbra is also surrounded by a penumbra When only the penumbra sweeps across Earth’s surface, the Sun isonly covered by the Moon. The Sun looks crescent-shaped - Annular Moon’s umbra falls short of Earth and no one sees a total eclipse The Moon appears too small to cover the Sun completely and a thin ring of light is seen around the edge of the Moon at mid-eclipse.o 3 types of lunar eclipses:- Total Earth has shadow with two parts: umbra and penumbraThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. A total lunar eclipse occurs when the Moon travels completely into the umbra. Occurs when the Moon is closest to Earth- Partial Part of the lunar surface passes through the umbra The Moon looks like it had a small bite taken out of it- Penumbral The Moon passes through only Earth’s penumbra The Moon still looks full, but it is not as bright and sometimes reddish in coloro There are several eclipses every year, but you are not always able to see them from where you live. You may need to travel in order to see one.o Total Solar Eclipse Statistics- On average, at a given place on Earth, expect to wait 360 years between 2total solar eclipses. The last total solar eclipse in Springfield, MO was on November 30, 1834. On August 21, 2017, there will be a total solar eclipse near Kansas City, Fulton, and St. Louis. Measuring Angleso Measuring angles is one of the oldest and most important jobs in astronomy.o An angle is the difference in direction between two different spots.- There are 360˚ in a full circle- Each degree is divided into 60˚ (arc minutes)- Each arc minute is made up of 60˚ (arc seconds)o The Small Angle Equation- How do we know the sizes of astronomical objects like the Moon, Jupiter, or the star alpha Centauri? We must have knowledge of the object’s distance and measure its angular size. We can then compute the actual size.- Equation: D → Diameter d → distance Θ → ThetaΘ = D/d To get arc seconds:D = Θ × d Small angle Θ is measured in arc seconds:D = _( Θ × d )_ 206, 265- Example: if the angular size of a full Moon is 1/2˚, what is its true diameter? First, convert degrees into arc seconds:Θ = ½ × _60˚ × _60˚ = 1800 arc seconds 1˚ 1˚ Next, determine the distance to the Moon d ≈ 384,000 km (about one quarter million mile) Finally, insert these values into the small angle equation:D = _( 1800 × 384,000) km_ 206265 And solve:D = 3,351 km (about 2000
View Full Document
Unlocking...