Astronomy Test 2 Review
What is apparent solar time and mean solar time?
*Apparent Solar Time*: time based on the sun's actual position in the sky (like a sundial), varies noon of one day to noon the next *Mean Solar Time*: averaged noon times, 24 hours long
What is meant by opposition, inferior conjunction, superior conjunction and greatest elongation?
*Opposition*: opposite to the sun *Inferior Conjunction*: object in between sun and earth (S-O-E) *Superior Conjunction*: sun in between earth and object (O-S-E) *Greatest Elongation*: object appears farthest from the sun in our sky
What is the difference between a sidereal day and solar day?
*Sidereal day*: how long it takes any *star* to go from its *highest point* in the sky one day *to* its *highest point* the next day (about 23 hrs 56 min) -star crossing meridian *Solar day*: how long it takes the *sun* to go from its highest point one day to its highest point the next day (about 24 hrs) -sun crossing meridian
Why is the sidereal year different from the tropical year?
*Sidereal year*: the time is takes Earth to complete one orbit relative to the stars *Tropical year*: how long it takes from one spring equinox to the next (20 min shorter than sidereal year)
What is the difference between a synodic month and sidereal month
*Synodic Month*: how long it takes the moon to go from one phase (full moon) to the same phase again (full moon), (about 29.5 days) *Sidereal Month*: moon's true orbital period, how long it takes the moon to orbit the Earth (about 27.33 days)
What is the sidereal and synodic period of a planet?
*Synodic Period*: the time it takes a planet from when it is lined up with the sun in our sky once to the next similar alignment *Sidereal Period*: the planet's orbit around the sun
How do time zones work?
24 Timezones, 15 deg wide, shifted slightly for convenience Going W- subtract 1 hour Going E- add 1 hour
What is standard time?
24 time zones, everyone uses same clock time
At what angle do stars rise and set in the local sky?
90 deg - Lat all stars rise and set at 50 deg at nyc
What is the concept of conservation of momentum and conservation of angular momentum?
Conservation of Momentum: the principle that, in the *absence of net force*, the total momentum of a system remains constant Conservation of Angular Momentum: the principle that, *in the absence of net torque*, the total angular momentum of a system remains constant
Know the coordinate system of latitude and longitude for the Earth and declination and right ascension for the celestial sphere.
Declination = Latitude, but +/- 90 deg from 0 deg equator Right Ascension = Longitude, but goes in a 360 deg circle measured in hours. Each hour of right ascension represents 15 deg. -0 hr is spring eq, 6 hr is summer sols, 18 hr is fall eq, 24 hr is winter sols.
What is Newton's law of gravity?
Fg = G (m1m2)/d² how you determine weight on other worlds
What are Newton's three laws of motion?
First law: an object moves at constant velocity if there is no net force acting upon it Second law: f = ma Third law: for any force, there is always an equal and opposite reaction force
What is the significance of the International Date Line, the Tropic of Cancer and the Tropic of Capricorn? Why are these lines located where they are?
IDL: cross E- subtract 24 hrs, cross W, add 24 hrs, on 180 deg longitude (opposite side of prime meridian) Tropic of Cancer: Northern most position you can see noon day sun overhead (23.5 deg N) Tropic of Capricorn: Southern most position you can see noon day sun overhead (23.5 deg S)
What is the difference between the Julian and Gregorian calendar?
Julian: 365 days, leap year every 4 years Gregorian: 365 days, leap year every 4 years except on millennials except is they are divisible by 400, synced with tropical year, this is the calendar we use today
What is kinetic energy and gravitational potential energy?
KE= 1/2mv² ; energy of motion PE= mgh ; stored energy g=9.81 m/s²
Know how to describe the local sky. Where is the celestial pole and celestial equator in the local sky?
NCP- same as latitude (NYC is +40 deg) Celestial Eq: 90-NCP (nyc: 90-40=+50 deg)
What is thermal energy and temperature?
TE= collective kinetic energy temperature= measures average kinetic energy
How does the phase of the moon affect the tides?
The sun and the moon work together to make make stronger tides, like during full or new moon. because gravity
What is acceleration?
a = ∆v/t
What is meant by center of mass?
balance point of system
Why do the astronauts experience weightlessness?
because they are in freefall
What is meant by tidal friction?
causes earth to slow down
What determines whether an orbit is closed (elliptical) or open (parabolic or hyperbolic)?
elliptical- less than escape parabolic- exact escape velocity hyperbolic- more than escape velocity
What does E=mc² mean?
energy = (mass)(speed of light)²
What is the concept of conservation of energy?
energy cannot be created nor destroyed; can only change form
What is force?
f = ma
What causes the tides?
gravity attracts the moon and the earth towards each other, but affects different parts of the earth differently
What is synchronous rotation?
moon's rotation on axis = moon's revolution around earth
What is escape velocity?
object gains enough orbital energy to escape from orbit
What is momentum?
p = mv
What is speed?
r = d/t , distance and time
What is a neap tide and spring tide?
spring tide: most extreme, full or new moon neap tide: least extreme, 1st quart or 3rd quart
What will happen to the length of the day, the distance of the moon and strength of the tides in the future?
the day will be longer the strength of the tides will decrease
What is universal time?
time on the prime meridian "Zulu time"
What is Daylight savings time?
turn clock ahead 1 hour, sun is on the meridian at 1 pm instead of noon
What is velocity?
v = ∆d/t, speed and direction
What is the declination and right ascension of the sun throughout the year
wave thing
What is the difference between mass and weight?
weight = mg F = ma