Download Integrative Studies 410 Our Place in the Universe

Scaling & Daily Motion
Scaling
• Often one is interested in how quantities
change when an object or a system is
enlarged or shortened
• Different quantities will change by different
factors!
• Typical example: how does the
circumference, surface, volume of a sphere
change when its radius changes?
How does it scale?
• Properties of objects scale like the
perimeter, the area or the volume
– Mass scales like the volume (“more of the same
stuff”)
– A roof will collect rain water proportional to its
surface area
Daily Rising and Setting
• Due to the rotation of the
Earth around its axis
• Period of rotation:
1 siderial day= 23h56m4.1s
• 1 solar day (Noon to Noon) =24h
• Stars rotate around the
North Star – Polaris
What time is it?
• Depends on where you are on the Earth!
• Time zones ensure that the noon is really
noon, i.e. sun is at highest point
• To avoid confusion, use universal time (UT),
the time at the meridian in Greenwich
UT = EST + 5 hrs
• Daylight savings adds one hour in spring, so
UT = EDT+ 4 hrs
The Time Zones
Established to insure that sun is at highest point
approximately at noon in the middle of the time zone
Daily and yearly motion intertwined
Solar vs Siderial Day
–
–
Earth rotates in 23h56m
also rotates around sun
 needs 4 min. to “catch
up”
Consequence: stars rise 4
minutes earlier each
night (or two hours
per month, or 12
hours in ½ year)
After 1/2 year we see a completely different sky at night!