ASTR 1514 1st Edition Lecture 5Objectives: - Understand how solar and lunar eclipses happen- Different kinds of eclipses- Why eclipses are so rare. 1.) Solar Eclipses: - Importance of a solar eclipse1) Measuring the duration of a solar eclipse allows us to measure the suns diameter, this can help us study the structure of the sun2) The discovery of helium – Using a spectroscope, Jules Cesar Jannsen observed aneclipse and noticed a yellow light with a wavelength that was different from any known element; this would later be known as helium 3) Demonstrates Einstein’s theory of General Relativity. Angular Size – The angle subtended by an object on the sky, both the moon and sun have an angular size of about 1 degree. During a Solar Eclipse: - The moon passes between the Sun and the Earth- Sun is “eclipsed” by the moon.- Happens only during a New Moon phase, however it does not occur at every New moon phase.These 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.- The moon and the sun have the same sized celestial disk, although the sun is 390 times bigger than the moon, the moon is 390 times closer, therefore the moon and sun have the same angular size. - Eclipses can take several hours from beginning to end, however a total eclipse will only last minutes. Diamond Ring Effect: The moment before a totality of a solar eclipse, when only a slight amount of the sun can be seen on the edge of the lunar disk, the event resembles a diamond ring. Solar Corona: The faint, outermost layer of the sun, can be seen during a solar eclipse. Understanding the Physics of shadows, from an extended light emitting object (with an angular size on the sky), can help us understand eclipses. - If the moon is directly between the sun and an observer standing on Earth, then the observer will not see the sun (Total eclipse).- If the moon is slightly offset from being directly between the earth and sun then the observer on Earth will see a portion of the sun, this a Partial Eclipse. - Umbra: Total Shadow – Total Eclipse (Darkest part of a shadow, cone-shaped region of full shadow cast by Earth, the moon, or another body during an eclipse. - Penumbra: Partial shadow – Partial eclipse. - Due to the rotation of the Earth; the shadow of a total eclipse moves fast, lasting only a few minutes. Annular Eclipse:- Because of the moon’s noncircular shaped orbit, it will be slightly different distances from the sun at different times in it’s orbit. (Further away moon appears to be smaller)- When this occurs then the sun’s angular size is a little larger than the moon’s, causing an annular eclipse.Overview of Solar Eclipses: 1) Happens at New Moon2) Moon passes between Earth and Sun3) Small portion of Earth can witness each one due to infrequent occurrences.2.) Lunar Eclipses- Happens at Full Moon phase- Earth is between the Sun and the Moon- The Earth is larger so it casts a larger shadow- Lunar eclipses are visible over a wider area of the Earth, and last a lot longer than a solar eclipse. - Moon appears to be red during a total lunar eclipse due to refracted red light (bluelight scattered away from the moon). Why don’t eclipses occur every month? Because the moon’s orbit is tilted about 5 degrees with respect to Earth’s orbit around the sun.*If the moon were further away from the Earth it’s angular diameter would