Assume the moon Praxis orbits the planet
Kronos in a circular orbit. The moon
is 0.1 AU from the planet. It takes 2 years for Praxis to orbit the
planet Kronos.
How fast is Praxis traveling? Give your answer in meters/sec and
miles/hour.
Hint: the following formulae may be useful:
Then you need to calculate how long it takes for the moon to orbit in seconds, t.
The radius of the orbit, R, is 0.1 AU, and the period of the orbit is 2 years.
convert distance to meters: d=(0.628 AU) x (1.496 x 1011 m / AU) = 9.4 x1010 m
convert time (t=2 yr) to seconds: t=(2 yr)(365 d/yr)(24 hr/d)(3600 sec/hr) = 6.3 x 107 s
calculate velocity: v=d/t = 9.4 x 1010 m/ 6.3 x 107 s = 1492 m/s
convert distance to miles: d=(9.4 x 1010 m ) ( 1 mile / 1609 m) = 5.84 x 107 mi
convert time to hours: t=(2 yr)(365 d/yr)(24 hr/d) = 1.75 x 104 hr
calculate velocity: v=d/t = 5.84 x 107 mi / 1.75 x 104 s = 3,337 mph
Fill in the blank:
A mile is a unit of distance.
An hour is a unit of time.
Miles per Hour is a unit of speed.
A parsec is a unit of distance
A lightyear is a unit of distance.
What observation did Galileo make which proved that the planets go around the sun? Explain.
Galileo's observation of the phases of Venus proved that the Earth travels around the sun. Other points: Galileo noticed that the stars were more numerous than previously thought and probably so far away that you would not notice their parallax movement. In addition Galileo noticed the moons of Jupiter orbiting the planet. By analogy the planets orbit the sun.
Why did Aristotle believe that the Earth is round? Explain.
Aristotle observed the shadow of the Earth on the moon during an eclipse is always circular. This means the Earth must be round. In addition if you walk north you see stars to the south falling below the horizon, implying the Earth must be round. In addition, the ancients thought that circles where perfect so it was natural for the earth to be round.
Using data from Table E.2 in the Appendix section of your text "The Cosmic Perspective," infer:
Mercury has no tilt and therefore no seasonal changes.
Uranus is closest to a 90 deg. tilt and therefore has the biggest change between seasons, Pluto also has a large change.
Note: Venus is almost 180 deg. of tilt so it like Mercury has very little change in the seasons.
Using Tables F.1 and G.1 in the Appendix section of your text "The Cosmic Perspective,"
calculate the distance to the following objects in meters, AU, and parsecs
To do this problem, read off the distance to the object in
light-years,
from the table. Convert the distance to the requested units using the
following conversions:
1 AU = 1.496 x 1011 m
1 ly = 9.46 x 1015 m
1 pc = 3.09 x 1016 m
For each object, circle which of the 3 units (meters, AU, or parsecs)
seems the easiest to use for that object.
There is no "wrong" answer to this part. It appears that it is
easiest to use
units such that the numbers are small integers. So for the Sun, using
AU is most convenient. (The distance to the sun actually defines this
unit scale.) For a star, parsecs or lightyears might be easier. For
a galaxy, parsecs, or "Mega-parsecs" (1 million parsecs = 1 x
106)
may be most convenient.
Recall the film we watched in class "The Powers of 10". Given the
distances you just calculated, approximately how many times further away is the Sombrero galaxy
compared
to the Sun?
Take the ratio of the distance to the Sombrero Galaxy to the distance
to the Sun.
3.16 x 1012 AU / 1 AU= 3.16 x 1012
so that galaxy is over a trillion times further away from the Earth than the sun is.