NATS 1570 Lecture Notes - Lecture 2: Kelvin, Hydrosphere
20 Jun 2018
School
Department
Course
Professor
NATS1570
Earth
Earth as a template
● We will use earth to compare to other smaller objects in the solar system
● In the last couple decades, the study of planets has become a study of geology
rather than astronomy
○ More and more of what we talk about are geological studies rather than
astronomical
○ This is in part because we can land probes on the planets to get their
geology, not just their orbits or their size
Position
● Earth is the third rock from the sun
● Position wise it is interesting, it is in that rare gap in the solar system where water can
exist in a solid/water/gas state
● Referred to as the Habitable Zone, because water is key
● We are about 70% water
● Any life found on another planet will use water for the same reasons we do
● Only if you are in the habitable zone could you potentially have water on your surface
● The habitable zone temperatures are going to run between 373K to 273K
● Kelvin scale, in science negative degrees are evil because they don’t mean anything
○ A negative degree doesn’t mean anything
○ From a scientific perspective you cannot do calculations with negative
degrees
○ 0 Kelvin is the coldest possible temperature
○ If you go up 1 degree Celsius you go up one degree Kelvin
○ 273K is about 0 degrees, whereas 373K is about 100C, between the boiling
and freezing point of water.
○ In Kelvin 0 is the coldest, in celcius -373 is the coldest
○ Saves scientists headaches for calculations
● A habitable zone is not a hard and fast definition, a number of other factors
determine whether a planet can have liquid water (its size, thickness of atmosphere,
etc.)
● The edges of a habitable zone are fuzzy, it is not just based on how close you are to
your star
● Earth sits in this habitable zone, mars and venus sit on its edges
● Our orbit takes little over a year, this distance from our sun only varies by a few
percent. The difference between near/far are not enough to change the temperatures
of its surface.
● We are closer to the sun in the northern hemisphere in January, the coldest part of
the year
● Stable orbit, climate is stable: winter cold, summer hot, not a huge variation
● Where do the seasons come from? Earth’s axis is tilted 23.5 degrees on its axis
○ Known this since 300BC
● Depending on how tilted you are from the sun you get more or less daylight.
Document Summary
We will use earth to compare to other smaller objects in the solar system. In the last couple decades, the study of planets has become a study of geology rather than astronomy. More and more of what we talk about are geological studies rather than astronomical. This is in part because we can land probes on the planets to get their geology, not just their orbits or their size. Earth is the third rock from the sun. Position wise it is interesting, it is in that rare gap in the solar system where water can exist in a solid/water/gas state. Referred to as the habitable zone, because water is key. Any life found on another planet will use water for the same reasons we do. Only if you are in the habitable zone could you potentially have water on your surface. The habitable zone temperatures are going to run between 373k to 273k.
