# NATS 1740 Chapter Notes -Lunar Eclipse, Shadow Falls, Minute And Second Of Arc

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Published on 13 Apr 2013
School
York University
Department
Natural Science
Course
NATS 1740
Professor
Astronomy Notes 1-5
Chapter 1
Horizon: divides the celestial sphere into the half you can see and the half you can't
Zenith: is the point directly above you on the celestial sphere
Meridian: is the line from north to south that passes through your Zenith
-Angels and angular distances on the sky smaller than degrees, we use Arcminutes and arcseconds
60 arcminutes = 1 degree
60 arcseconds = 1 arcminute
- 1 arcminute is the smallest separation your eyes can see/notice
Constellation: is a grouping of stars in a specific area of the sky
Chapter 1.3, 2.1, 2.2
When Earth is rotating its orbiting the sun completing one orbit each year.
- Average orbital distance is called Astronomical Unit
- AU = 150 million kilometers
Ecliptic plane: the plane of Earth's orbit around the sun
Axis Tilt: The amount by which a planet's axis is tilted with respect to a line perpendicular to the ecliptic
plane
Local sky: the sky as seen from where you're standing
Circumpolar: Stars near the north celestial pole that do NOT rise or set
- Circumpolar stars remain above the horizon and make daily counter clockwise circles around the North
Celestial pole.
- Stars near the South Celestial pole never rise above the horizon
Reasons for Seasons (2.2)
-longer/warmer days in the summer
-shorter/colder days in the winter (why?)
-Because the tilt of Earth's axis causes sunlight to fall different on Earth at different times of the year.
-The steeper the angle= more sunlight hitting the earth is more concentrated (vise versa)
Summer (June 21) Solstice = Northern Hemisphere tilted mostly directly towards the sun
Winter (December 21) Solstice = Northern Hem. tilted away from the sun
Spring (March 21) Equinox = N. Hem. goes from being tilted away from the sun to slightly towards it
Fall (September 22) Equinox = N. Hem. starts tilting away from the sun
Moon Phases
Waxing = Increasing
Waning = Decreasing
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New crescent = Waxing crescent
Old crescent = Waning crescent
Lunar eclipse: When earth is between the sun and the moon (Earth's shadow falls on the moon)
Solar eclipse: When the moon is between the earth and the sun (Moon's shadow falls on the Earth [sun
is blocked])
Umbra: Where sunlight is completely blocked
Penumbra: Where sunlight is partially blocked
Ancient mystery of planets 2.4
Retrograde motion: (Backwards) composed to the norm
Stellar parallax: the apparent shift in the position of a nearby star (relative to distant object) that occurs
as we view the star from different positions in Earth's orbit of the sun each year.
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Chapter 3 The Science of Astronomy
Sun - > Sunday
Moon -> Monday
Mars -> Tuesday
Mercury -> Wednesday
Jupiter - > Thursday
Venus - > Friday
Saturn - > Saturday
In ancient times they would track the days of the week by what was visible by the naked eye in the sky.
-Determining time of day -> path of the sun or moon
-Determining seasons -> used manmade structures
-Modern science emerged from the Mediterranean and the middle east especially Ancient Greece.
Kepler's First Law
-Kepler discovered that the planets orbit the sun in ellipses with the sun at one focus.
- The distance between the planet and the sun is called orbital radius
- The average orbital radius is equal to the semi major axis regardless of eccentricity
-Eccentricity = e = c/a
For a circle the eccentricity e=0 Since the foci coincide (c=0)
Example: Neptune's orbit is nearly circular and its average orbital radius is 30 AU. Pluto's average orbital
radius is 40 AU. what would be the minimum eccentricity of Pluto's orbit for Pluto to sometimes be
closer to the sun than Neptune.
a) 0.1
b) 0.25 40AU *0.25 = 10 AU
c)0.5
d)0.7
e) 0.95
Kepler's Second Law
-An object moves faster in its orbit when it is closer to the sun, so that the line connecting the object
around the sun sweeps out equal areas in equal times
Keplers Third Law
-For objects orbiting the sun, the square of the objects orbital period (P), measured in years, equals the
cube of its semi major axis (a), measured in astronomical units. p2=a3
Example: p2=a3 sqr = Square root, cubed =3
Jupiter
AU= 5
a= 125
p= ?
p = sqr5cubed = sqr125 = 11.1 years
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## Document Summary

Horizon: divides the celestial sphere into the half you can see and the half you can"t. Zenith: is the point directly above you on the celestial sphere. Meridian: is the line from north to south that passes through your zenith. Angels and angular distances on the sky smaller than degrees, we use arcminutes and arcseconds. 1 arcminute is the smallest separation your eyes can see/notice. Constellation: is a grouping of stars in a specific area of the sky. When earth is rotating its orbiting the sun completing one orbit each year. Average orbital distance is called astronomical unit. Ecliptic plane: the plane of earth"s orbit around the sun. Axis tilt: the amount by which a planet"s axis is tilted with respect to a line perpendicular to the ecliptic plane. Local sky: the sky as seen from where you"re standing. Circumpolar: stars near the north celestial pole that do not rise or set.