## ....Introductory Astronomy...YouTube Videos: Math Review, Distance Scales, Kepler's Laws, Newton, Gravity, Relativity, Sun, Planets future....Telescopes and more

Sections on this page:
[UNIT 1: Powers of 10, Scientific Notation, Supermoon, Distances, Kepler's Laws]

[UNIT 2: Newton's Laws, Gravity, Orbits, Relativity ]

[UNIT 3: Light, Telescopes, Moon ]

[UNIT 4: ]

[UNIT 5: ]

 Unit 1 Powers of 10, Distances in Solar System, Orbits, Kepler's Laws Powers of 10 Basics, Scientific Notation Example (11 minutes) "Powers of 10" or "Scientific Notation" is used to conveniently represent very large or very small numbers. This video describes how the powers of 10 are determined and how various numbers can be written using powers of 10 notation. Powers of 10, Scientific Notation, Multiply, Divide Example (14 minutes) This video shows how to multiply and divide numbers represented by powers of 10, or scientific, notation. The video ends with some examples of powers of 10 calculations for astronomy. ...................................... Supermoon, Solar Eclipse Example (14 minutes) This video explains the term "supermooon" by calculating the apparent angular size of the Moon when it is close to the Earth in its orbit and when it is far away from the Earth. In the last half of the video the apparent angular size of the Sun is calculated. The conditions necessary for a total solar eclipse are discussed using the angular sizes of the Moon and Sun. Please note that a solar eclipse occurs at the phase of new moon, not full moon. Distance Scales for Solar System Example (9 minutes) Data for distances in the solar system are shown. Then, the distances to objects near the Sun are calculated for the case when the Sun is represented by a basketball. This exercise may improve your appreciation for the very large distances that exist between objects in and near the solar system. Distance Ratios for the Solar System Example (5 minutes) This video calculates various ratios of radii and distances in the solar system. The purpose of these calculations is to give the viewer an idea of the sizes of objects in our solar system. Please view my Powers of 10 video if you are not familiar with scientific notation. Introductory Astronomy Physics Prof. Greg Clements Eratosthenes Calculates Radius of Earth Example (10 minutes) This video shows how Eratosthenes determined the approximate radius of the Earth. The data available were the angle of the shadow of the Sun in Alexandria, the distance between Alexandria and Syene, and the fact that the Sun was overhead in Syene Egypt on the June Solstice. The method of proportions is used to find the circumference of the Earth. The formula for circumference in terms of radius is used to calculate the radius of the Earth. Altitude of North Celestial Pole Example (12 minutes) This video shows that the altitude of the North Celestial Pole is equal to the latitude of the observer in the Northern Hemisphere. The video defines altitude, zenith, celestial equator, north celestial pole, and meridian. Diagrams are used to determine the altitude of the NCP. ...................................... Sidereal and Synodic Period, Sketch Example and Calculation Example (20 minutes) This video gives the definitions for sidereal and synodic periods. The synodic period of Venus as viewed from the Earth is approximately determined using a sketch. The values for synodic periods are calculated for Venus and the outer planets in the solar system. Kepler's First Law Example Earth Mars Example (12 minutes) This video explains Kepller's First Law and eccentricity. The eccentricity of Earth's orbit is calculated given the aphelion and perihelion distances. The aphelion and perihelion distances for the orbit of Mars are calculated from the eccentricity and semimajor axis values. Kepler's Second Law, Speed of Earth at Perihelion Example (6 minutes) This video explains Kepler's Second Law for Planets and calculates the speed of the Earth at perihelion given the speed at aphelion and the distances from the Sun at perihelion and aphelion. Kepler's Third Law, Perihelion of Halley's Comet Example (9 minutes) This video explains Kepler's Third Law for planets. Calculations are done to find period and semimajor axis values. The perihelion distance for Halley's Comet is calculated given the semimajor axis and eccentricity values. ...................................... . Return to the top of this page. ... OR ... Return to physics.gpclements.com
 Unit 2 Newton's Laws, Gravity, Orbits, Relativity Newton's Three Laws of Force Example (7 minutes) This video discusses Newton's Three Laws of Force. The situations discussed are 1) zero net force, 2) a single force, 3) pairs of forces that act on different objects. Force of Gravity: Earth and Moon Example (5 minutes) This video uses Newton's Law of Gravitation to calculate the force of gravity for the earth pulling on the Moon and the Moon pulling on the Earth. Newton's Third Law is discussed. Gravity, Orbits, Speed of Hubble Telescope in Orbit Example (7 minutes) The orbital speed of the Hubble Telescope is calculated in this video. Newton's Gravity formula is used for the centripetal force. The altitude of Hubble's orbit is used to find the total distance from the center of the Earth to the center of the Hubble Telescope. ...................................... Escape Velocity from Earth, Moon, Mars, Ceres Example (8 minutes) The concept of escape velocity is discussed. The escape velocity is calculated for the Earth, Moon, Mars, and Ceres. The effect of an atmosphere is ignored. Acceleration Due to Gravity for Earth, Moon, Mars, Ceres Example (6 minutes) The acceleration due to gravity is calculated for the Earth, Moon, Mars, and Ceres. ...................................... E = mc^2 Energy Mass Example (8 minutes) In 1905 Einstein revealed to the world the connection between mass and energy. This video calculates the amount of mass needed to supply energy to a city of 200,000 homes for one year. ... Return to the top of this page. ... OR ... Return to physics.gpclements.com
 Unit3 Light, Telescopes, Moon Light, Wavelength, Frequency, Energy, UV and Yellow Light Example (6 minutes) The frequency of light and the energy of one photon are calculated for UV B and Yellow light. The wavelengths are given. Hydrogen Spectral Line Using Bohr Model, Energy, Frequency, Wavelength Example (10 minutes) A brief description of the Bohr model of the hydrogen atom is given. The energy, frequency, and wavelength of light are calculated as the electron changes energy level from n=3 to n=2. ...................................... Calculate Sun's Radius Using Blackbody Formulas Example (9 minutes) In this video the Sun is assumed to be a Blackbody. The power output and peak wavelength for the spectrum of the Sun are given. The effective temperature, area, and radius of the Sun are calculated. Betelgeuse Radius Using Blackbody Formulas Example (7 minutes) The distance to Betelgeuse is not well known. Using an estimate for the power output for the star and the wavelength of the peak of the spectrum, the equations for blackbodies are used to calculate the effective temperature for Betelgeuse and its radius. ...................................... Mars Subsolar Temperature Using Albedo and Blackbody Equation Example (8 minutes) The temperature of a location on Mars where the Sun is directly overhead is calculated. The calculation uses the adjusted value for the solar constant due to Mars being farther from the Sun than the Earth. The calculation uses the albedo of Mars to reduce the power absorbed. The power radiated from Mars soil is calculated using the assumption that the soil acts like a Blackbody. Temperature on Moon With Sun Overhead, Blackbody Equation Example (9 minutes) This video calculates the temperature on the Moon for a location where the Sun is "overhead." The solar constant at the Earth is used. It is assumed that the Moon absorbs 89% of the incoming sunlight. The power radiated by 1 square meter on the Moon is calculated using the equation for a Blackbody. The equilibrium temperature is found where the energy absorbed per second equals the energy emitted per second by the 1 square meter area on the Moon. Habitable Zone Location Calculation Using Blackbody Equation and Albedo Example (15 minutes) The inner and outer boundary for the habitable zone around the Sun are calculated using the assumption that the planet is a blackbody. The effect of albedo and Greenhouse are estimated and used in the calculation. The basis for the calculation is that the power absorbed by the planet equals the power emitted by the planet. The planet is assumed to be rotating rapidly. Why Do Sunspots Appear To Be Dark? Example (9 minutes) Sunspots appear to be dark in comparison to the surrounding photosphere. The powers emitted by one square meter of photosphere material and by one square meter of sunspot material are calculated using a Blackbody equation. The ratio of the powers is calculated. The wavelength of the peak of the Blackbody spectrum is calculated for both regions. Our eyes do not detect light at the wavelengths near the peak of the Blackbody curve for the sunspot material. ...................................... Doppler Shift of Light From Edge of Sun Example (8 minutes) Light from the edge of the Sun is shifted in wavelength due to the motion of the edge of the Sun toward (and away from) the Earth. The speed of approach is calculated given the radius of the Sun and the number of days for it to spin once at its equator. The amount of Doppler Shift for the hydrogen alpha spectral line is calculated. Doppler Shift Andromeda Galaxy and Collision with Milky Way Example (9 minutes) The Doppler Shift of the hydrogen alpha spectral line is calculalted for light from the Andromeda Galaxy. The Andromeda Galaxy is moving towards the Milky Way Galaxy so the shift is a "blue" shift to a slightly shorter wavelength. The distance to Andromeda and the speed of approach are used to calculate the approximate time until the two galaxies collide. Recent (2012?) observations from the Hubble Telescope show that the two galaxies will collide as the sideways motion of Andromeda is not high enough to cause the two galaxies to miss as they move towards each other. My calculation for the time to collision is less than what I commonly read in web sites. Please leave a comment if you see an error in my calculation. ...................................... Telescope Magnification Example (5 minutes) The magnification calculation is explained and demonstrated. The video explains why the eyepiece is changed rather than the objective of the telescope. The video gives a rough guideline for the maximum magnification that should be used for a telescope Telescope Light Gathering Power Compared to Human Eye Example (5 minutes) The light gathering powers of the Hubble Telescope and a 4 inch diameter telescope are compared to the average, dark adapted, human eye. The ratio of the squares of the diameters of the openings are used to compare the light gathering powers. Is not necessary to first find the radius of the openings. Telescope Resolving Power, Minimum Size of Crater Seen on Moon Example (12 minutes) The resolving power of the eye and a 4 inch diameter telescope are calculated. The minimum size of a resolved (clearly seen) feature on the Moon is calculated. The effect of "twinkling" atmospheric blurring of images is briefly discussed. ...................................... Find Synodic Period of Moon Given Sidereal Period 3 Methods Example (15 minutes) Three different methods are used to determine the synodic period of the Moon given the sidereal period of the Moon. Method 1 is a graphical, trial and error method. Method 2 is an analytic solution. Method 3 uses a well known astronomy formula that relates sidereal and synodic periods of the object and the Earth's period. ... Return to the top of this page. ... OR ... Return to physics.gpclements.com
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 Unit 5 ...................................... ...................................... ...................................... ... Return to the top of this page. ... OR ... Return to physics.gpclements.com