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parallels that run east and west at equal distance, measure north and south of Equator starting at 0 degrees
-latitude determines which stars you will see. Some stars will never be seen because of the location - the Earth gets in the way |
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| meridians; run north and south, measure east and west of Prime Meridian in Greenwich, London |
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| approximately 25,000 miles at the equator (24,901.55 miles). A bit shorter if measured at the poles (24,859.82 miles) because of gravity |
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-about 109 times larger than the earth
-surface temp is about 5800 K |
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| circumference of the Earth's orbit is about 574,380,400 miles. |
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rotates on its axis counter clockwise, west to east, (if you were looking down at the North Pole), 360 degrees, in 1 day (24 hours)
15 degrees = 1 hour
-approx. speed of rotation at equator is 1,037 miles per hour
- revolves around the sun |
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It is the point where the planet in orbit is furthest from the sun. For Earth this is on July 4 (summer).
It is the point where the planet in orbit is furthest from the sun. |
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| the point where the planet in orbit is closest to the sun. We are actually closer to the sun on January 3 (winter), than in summer (July 4) when we are furthest from the sun |
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| uses the Earth's equator as a guide to slice the sky in half |
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an extension of latitude in the sky, also given in degrees and minutes
We use time (minutes) to represent location in the sky.
declination goes from - 45 degrees, up and over our heads to +45 degrees = 90 degrees total. Negative declination in Southern Hemisphere, Positive declination in Northern Hemispher |
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an extension of longitude in the sky, given in hours
15 degrees = 1 hour |
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| the point that corresponds to the coordinates (0".0") in the celestial sphere. We "stop" the earth at this point at noon. Descriptions of location are based on this location. We need to figure out where we are located in relation to this point. |
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| Question: What is the declination of Polaris assuming whole number? |
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| Polaris is always at 90 degrees declination. |
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| Question: What is the range of values of declination that are in your celestial sphere? |
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The intersection plane of the earth's orbit with the celestial sphere, along which the sun appears to move as viewed from the earth.
All planets line up in a relatively straight line with Earth |
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| we are at a 23.5 degree tilt off our axis |
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"equal" - equal day, equal night; 12 hours of day and 12 hours of night on every location of the planet
Happens 2 times each year |
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| June 21, longest day of the year in the Northern Hemisphere (shortests day in the Southern) |
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| December 21 - shortest day of the year in Northern Hemisphere |
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| divides the earth exactly in 1/2: 1/2 in light and 1/2 in darkness |
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| Always lined up at 90 degrees declination. |
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| Is shorter than a solar day by 4 minutes. A sidereal day is 360 degrees. |
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| is about 4 minutes longer because you must rotate a little bit longer for the sun to be in the same location in the sky. |
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energy undulating from a source to a receiver
- light is either absorbed, refracted or reflected |
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light goes in the same direction it came from
Light does not penetrate
This is "mirrors" |
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| light goes through an object and then is bent; light converges to a focal point |
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| important for magnification |
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| the color things appear to us represents what wavelength is absorbed. |
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indicates the temperature that the star is radiating; if it's white,then all wavelengths in the visible spectrum are being radiated.
Hotter stars appear blue
Cooler stars appear red |
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the distance light travels at the speed of light in one earth year
- 4.2 light years away means it takes 4.2 years for its light to reach us.
Light travels constantly at the spee of light. So, we are actually seeing into the past,because years have already gone by, by the time the light reaches our planet.
How many light years is the sun away from us?
Use speed (c) = 670,616,629.38 mph
D = 97,000,000 miles
Earth year = 365.25 days |
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| angle of incidence is equal to the angle of reflection - only on a flat surface |
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| the image seen depends on the distance the object is away from the mirror and the distance the receiver is from the mirror. |
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| telescopes - focal length |
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the convergence of the reflected or refracted rays of light
focal length varies due to the size of the curvature in the mirror of the lens |
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| usually have two lenses, one of these is curved |
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| telescopes need two things |
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| an opening to let light in and an eyepiece |
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nearest star is 4.2 light years away from our sun - alpha centauri
stars are self luminous and produce energy by means of nuclear fusion reactions
- we learn about stars through the light they give off, color of light indicates heat of the star |
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| distance of stars - the parallax |
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| you calculate distance based on degrees of angle change from one time to another |
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| is backwards to what we think. The lower the numerical value, the hotter the star and the brighter |
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| how bright the star looks to us from earth |
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the apparent magnitude if a star was placed at a distance of 10 parsecs
Absolute magnitude is the same as apparent magnitude if both stars were at a distance of 10 parsecs. |
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| star classification = through spectral class |
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most commonly classified by surface temperature
spectral class |
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| the number of waves that pass by a fixed point in a given time |
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| a star located exactly 10 parsecs away |
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| will have the same absolute and apparent magnitude |
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| a star located further than 10 parsecs away |
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| will have an apparent magnitude which is numerically bigger than its absolute magnitude. So, the absolute magnitude will be fainter |
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| a star located closer than 10 parsecs away |
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| the apparent magnitude will be numerically smaller than the absolute magnitude so its apparent magnitude will be brighter than its absolute magnitude |
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