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Vocabulary
looking at the sky, light, telescopes, stars, sun
47
Astronomy
Undergraduate 1
07/28/2009

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Term
latitude lines
Definition
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
Term
longitude lines
Definition
meridians; run north and south, measure east and west of Prime Meridian in Greenwich, London
Term
circumference of Earth
Definition
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
Term
sun
Definition
-about 109 times larger than the earth
-surface temp is about 5800 K
Term
orbit of Earth
Definition
circumference of the Earth's orbit is about 574,380,400 miles.
Term
Earth's rotation
Definition
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
Term
aphelion
Definition
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.
Term
perihelion
Definition
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
Term
celestial equator
Definition
uses the Earth's equator as a guide to slice the sky in half
Term
Declination (dec)
Definition
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
Term
Right Ascension (RA)
Definition
an extension of longitude in the sky, given in hours
15 degrees = 1 hour
Term
vernal equinox
Definition
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.
Term
Question: What is the declination of Polaris assuming whole number?
Definition
Polaris is always at 90 degrees declination.
Term
Question: What is the range of values of declination that are in your celestial sphere?
Definition
Term
ecliptic
Definition
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
Term
axile tilt
Definition
we are at a 23.5 degree tilt off our axis
Term
equinox
Definition
"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
Term
June Solstice
Definition
June 21, longest day of the year in the Northern Hemisphere (shortests day in the Southern)
Term
December solstice
Definition
December 21 - shortest day of the year in Northern Hemisphere
Term
circle of illumination
Definition
divides the earth exactly in 1/2: 1/2 in light and 1/2 in darkness
Term
Polaris
Definition
Always lined up at 90 degrees declination.
Term
sidereal day
Definition
Is shorter than a solar day by 4 minutes. A sidereal day is 360 degrees.
Term
solar day
Definition
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.
Term
light wave
Definition
energy undulating from a source to a receiver
- light is either absorbed, refracted or reflected
Term
speed of light (C)
Definition
670,616,629.38 mph
Term
absorbed
Definition
light penetrates
Term
reflected
Definition
light goes in the same direction it came from
Light does not penetrate
This is "mirrors"
Term
refracted
Definition
light goes through an object and then is bent; light converges to a focal point
Term
focal length
Definition
important for magnification
Term
wavelengths
Definition
the color things appear to us represents what wavelength is absorbed.
Term
star color
Definition
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
Term
light year
Definition
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
Term
Law of Reflection
Definition
angle of incidence is equal to the angle of reflection - only on a flat surface
Term
image seen
Definition
the image seen depends on the distance the object is away from the mirror and the distance the receiver is from the mirror.
Term
telescopes - focal length
Definition
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
Term
telescopes -
Definition
usually have two lenses, one of these is curved
Term
telescopes need two things
Definition
an opening to let light in and an eyepiece
Term
star descriptions
Definition
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
Term
distance of stars - the parallax
Definition
you calculate distance based on degrees of angle change from one time to another
Term
magnitude
Definition
is backwards to what we think. The lower the numerical value, the hotter the star and the brighter
Term
apparent magnitude
Definition
how bright the star looks to us from earth
Term
absolute magnitude
Definition
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.
Term
star classification = through spectral class
Definition
most commonly classified by surface temperature
spectral class
Term
wavelength frequency
Definition
the number of waves that pass by a fixed point in a given time
Term
a star located exactly 10 parsecs away
Definition
will have the same absolute and apparent magnitude
Term
a star located further than 10 parsecs away
Definition
will have an apparent magnitude which is numerically bigger than its absolute magnitude. So, the absolute magnitude will be fainter
Term
a star located closer than 10 parsecs away
Definition
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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