Astro 120: Fall 2005
The Sky and the Solar System(s)
Review Sheet 1
NOTE: EXAM 1 is September 29 at 6:30pm
Part I: The Sky, an Introduction - Basic Concepts
General scales of the Universe:
- the astronomical unit
- solar system distances and sizes
- the light year.
- Coordinate Systems
- The Horizon system of coordinates (Altitude/Azimuth).
- advantages and disadvantages of such a Local Coordinate system
- The concept of the Latitude and Longitude to measure positions on
- The Prime Meridian (Greenwich Meridian) at
Longitude =0 degrees.
- Celestial Coordinates:
- Right Ascension (Celestial Longitude)
and Declination (Celestial Latitude).
- Celestial North and South poles as extensions of the Earths
North and South Poles
- The Celestial Equator
- Zero point of Right Ascension = Vernal Equinox.
- Division of celestial longitude into Hours instead of
degrees (24hrs=360 degrees).
- Right Ascension INCREASES to the East from the Vernal Equinox.
- The Autumnal Equinox at RA=12 hrs, Dec=0 degs.
- the altitude of the Celestial Poles and the highest point
on the Celestial Equator from any latitude on the Earth.
The Sun and its Path on the Sky
- the Ecliptic Plane (the plane containing the orbit of the
Earth around the Sun.
- The Seasons
- tilt of the Earth away from the vertical relative to the
Ecliptic (The angle of Obliquity= 23.5 degrees for Earth).
- effect of this tilt on the amount of sunlight reaching various
part of the Earth at various times of the year.
- reasons why the its usually much colder in
the winter than summer at mid-northern latitudes of the Earth.
- the apparent path of the Sun on the Celestial sphere.
- passes through the Vernal Equinox moving North
(in Spring; March 20/21) at RA=0 Dec=0,
- reaches Dec=23.5 deg and RA=6hrs on June 20/21(Summer Solstice),
- back to the Equator (Dec=0) at RA=12hrs on Sept 20/21
- most southerly Dec=-23.5 deg at RA=18hrs (Winter Solstice).
- maximum altitude at noon at various times of the year.
- (Should be able to draw a meridian diagram for the Sun
as it transits the local meridian)
The Moon and its Phases
- Synodic and Sidereal Month and reason why one is longer than the other.
- Phases of the moon; inverse relationship of the Earth's phases as
seen from the Moon.
- relationship between the phases of the moon, the time
of day and the appearance of the moon in the sky.
- the moon always has the same face towards the Earth
- The tilt of the Moon's orbit relative to the Ecliptic (Earth-Sun plane).
- Where is the _____ moon in the sky at ____ time of day?
Path of Moon on Sky; Eclipses
- path of the Moon on the celestial sphere and its relationship to the
path of the Sun.
- crossing points of the Moon's orbit and the Sun's path
on the sky (nodes)
- significance of the Lunar nodes for the occurrence of Eclipses
- Properties of shadows of planetary bodies
- definition of total, partial and annular solar eclipses
- frequency and visibility of lunar and solar eclipses
- Lunar eclipses and their relationship to solar eclipses
- Ancient Greeks
- how they determined the Earth was round
- how they showed its approximate size.
- Copernicus and the Sun centered universe.
- Tycho Brahe and Kepler
- Galileo and his experiments with gravity.
- Kepler's law's of planetary motion.
- 1st Law of Ellipses,
- 2nd Law of Areas (and relative speed in orbit)
- 3rd Law of Periods (p*p = a*a*a).
- Concept of eccentricity (e) and semi-major axis of ellipse.
- Physical picture of an elliptical orbit.
Newton and Gravity and Newton's Laws of Motion
- Sir Isaac Newton
- Newtonian Concept of Gravity
- Gravity as a central force
- Newton's 3 laws of motion.
- The motion of Moon - as a falling body
- Newton's explanation of Kepler's Laws in terms of a theoretical model of gravity.
- Orbital mechanics and interplanetary orbits:
- how to get to Mars via a
- Gravity assist to the outer planets.