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Star Types

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There are 4 fundamental forces of nature: Strong nuclear - this keeps protons close together Weak nuclear a responsible for radioactive decay Electromagnetism - light, electricity, magnetism, etc Gravity - weakest of all, but furthest reaching A star (Latin root stella-) is essentially a ball of gas powered by nuclear reactions, held together by gravity. Stars may appear white, but their color is a combination of many colors (and non visible e-m waves like UV). Spectral types are listed in order of decreasing temperature: O B A F G K M with a temperature range from 60,000 K down to under 3500 K. There are further subdivisions (C and S stars under M). You can learn a lot about a star from where it lies on the Hertzsprung-Russel diagram. The H-R diagram plots magnitude (brightness, from dim to bright) vs. temperature (high to low, usually as spectral type). Hottest stars are on the left if the graph - they are normally brighter than cooler stars. Most stars fal
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Full (blue) Moon info here

http://www.fullmoon.info/en/blog/fullmoon-blue-moon.html
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Magnitude etc.

Angular Measurement Consider the following convention which has been with us since the rise of Babylonian mathematics: There are 360 degrees per circle. Each degree can be further divided into 60 minutes (60'), each called an arcminute. Each arcminute can be divided into 60 seconds (60"), each called an arcsecond. Therefore, there are 3600 arcseconds in one degree . Some rough approximations: A fist extended at arm's length subtends an angle of approx. 10º. A thumb extended at arm's length subtends an angle of approx. 2º. The Moon (and Sun) subtend an angle of approx. 0.5º. Human eye resolution (the ability to distinguish between 2 adjacent objects) is limited to about 1 arcminute – roughly the diameter of a dime at 60-m.  Actually, given the size of our retina, we're limited to a resolution of roughly 3' So, to achieve better resolution, we need more aperture (ie., telescopes). The Earth's atmosphere limits detail resolution to obje
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Online Orreries

https://in-the-sky.org/solarsystem.php http://www.theplanetstoday.com/ https://www.fourmilab.ch/solar/ http://www.fourmilab.ch/earthview/vplanet.html https://www.fourmilab.ch/cgi-bin/Solar/action?sys=-Si
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Brief history of 1500 years of astronomy

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Ptolemaic Universe (geocentric) http://astro.unl.edu/naap/ssm/animations/ptolemaic.swf The most important things to get out of this are: - Epicycles were a very useful way to (wrongly) explain why retrograde motion happened with planets. - Precession (the wobbling of the Earth) causes us to have different North Stars (or no North Star) at various points over the course of thousands of years.  Thus, star maps are not accurate after several hundred years.  However, this was not understood until the time of Newton and others. Nicolaus Copernicus, 1473 - 1543 http://astro.unl.edu/naap/ssm/animations/configurationsSimulator.html Galileo Galilei, 1564 - 1642 Galileo and his telescope: moon craters moons of Jupiter phases of Venus "rings" of Saturn stars in the Milky Way sunspots Speaking of sunspots: http://galileo.rice.edu/sci/observations/sunspot_drawings.html Johannes Kepler, 1571-1630 - his laws (shown below) are based o
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Coordinate Systems

Celestial Sphere - points to know: - Both Equinoxes - Both Solstices Celestial north Celestial south Ecliptic Celestial equator Coordinates : On Earth: Longitude half-circle lines from North to South pole Zero longitude runs through the site of the Royal Greenwich Observatory in England - the Prime Meridian (0 degrees long.) Number of degrees east or west of the PM Latitude Full circle lines parallel to the equator (0 degrees latitude) + or - 90 degrees corresponds to the poles International Date Line (IDL) Near or along 180 degrees longitude line, through the Pacific Ocean As we travel eastward around the globe, the hours get later roughly each 15 degrees (a time zone). When we cross the IDL, we go BACK one day. This keeps only 24 hours on the Earth at a time. In the Sky: Celestial Equator - imaginary line above the Earth's equator Right Ascension (RA) Celestial analog of longitude (both measure east-west) Measured in hours (each hour of RA equals 15 degrees) along the celestial
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Celestial Sphere concept

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Celestial Sphere Celestial sphere sites The first site allows you to simulate the apparent motion of the Sun around the Earth for any day of the year (and location).  It's really cool to play around with. http://astro.unl.edu/naap/ motion3/animations/sunmotions. swf http://www.astronomynotes.com/ nakedeye/csph1t5.htm http://www.astronomynotes.com/ nakedeye/s4.htm > The analemma - the "apparent" path of the Sun around the Earth
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