iii. Inverse Square Law of Radiation:1. Diluted version of light deals with how far or close you are to the light sourcea. The closer you are to light source, the less diluted the lightb. You have 1 square unit and as you move out twice as far, you see that light split up into 4 parts (so ¼ of the light you will get)a. The atmospheres of stars produce absorption line spectra, depending on the presence of different ELEMENTS  tells you COMPOSITION!i. Coolest stars have lots and lots of absorption bandsii. O B A F G K M (sequence of temperature)ASTRON 89 1nd Edition Lecture 16Outline of Last Lecture I. The Sun’s Chromosphere II. The Sun’s Corona III. Solar Wind IV. Introduction to Properties of Stars Outline of Current Lecture I. Properties of Stars: Distance II. Properties of Stars: Luminosity and Apparent Brightness III. Classifying Stars: Spectral ClassesCurrent LectureI. Properties of Stars: Distance a. D = distance to a star in parsecsi. 1 pc = 3.26 ly ii. Distance at which one AU subtends an angle 1 arc second (makes an angle at 1 arc secondiii. That angle is measured perpendicular to the observer1. S line of sightb. P = parallax angle of that star in arc secondsi. This relationship means closest stars have greatest parallaxii. Closer to objects, larger the angle. The ANGLE between two objects in thesky is what you are measuring and the smaller the angle gets, the further away that object isc. D= 1/P INVERSERELATIONSHIPi. If the angle is less than 1 arc second, then the distance has to be GREATERthan 1 parsec (greater than 3.26 ly)II. Properties of Stars: Luminosity and Apparent Brightness a. Once angle gets to be very small for really far away objects, you cannot measure that anymore. So there are other ways of figuring out distance of a starb. Luminosity (intrinsic brightness, absolute brightness) and apparentbrightnessi. Luminosity: measure of the energy per second ii. Apparent brightness: apparent brightness = luminosity / (distance)^2These 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.iii. Inverse Square Law of Radiation: 1. Diluted version of light deals with how far or close you are to the light sourcea. The closer you are to light source, the less diluted the light b. You have 1 square unit and as you move out twice as far, you see that light split up into 4 parts (so ¼ of the light you will get) 2. Is you’re 3 times farther away, there are 9 units that light splits up into so you only get 1/9 of the lighta. 4pi*r^2 = area of the sphereIII. Classifying Stars: Spectral Classesa. The atmospheres of stars produce absorption line spectra, depending on the presence of different ELEMENTS  tells you COMPOSITION! i. Coolest stars have lots and lots of absorption bandsii. O B A F G K M (sequence of temperature) b. Spectral classes that is for classifying