Unit Two Measuring The Earth

I. The Earth’s Shape A. Evidence the earth is round: Ships gradually disappear over the horizon from the bottom up when sailing away.

The altitude to Polaris changes as location changes north to south. If the earth was flat, Polaris would be at the same altitude, and visible, from every location.

The shadow of the earth on the moon during a lunar eclipse is round. The best evidence is: Photographs taken from space. They provide direct evidence of the earth’s shape.

B. The Precise Shape Measurements of weight differ from the poles to the equator. An object is found to weigh more at the poles than at the equator.

Weight is influenced by the pull of gravity on an object. The closer an object is to the center of the earth, the greater the pull of gravity. The poles must be closer to the center of the earth for an object to weigh more.

Analysis of polar and equatorial diameters indicate that the earth is slightly flattened at the poles and bulging at the equator. The precise shape of the earth is an oblate spheroid.

This difference in diameter is immeasurable when compared to the size of the earth. When drawn to scale, the earth must be represented as a perfect circle.

The polar diameter is only 42 km smaller than the equatorial diameter. The polar diameter is: 12,714 km The equatorial diameter is: 12, 756 km

The height and depth of objects on the earth’s surface are insignificant when compared to the size of the earth. When drawn to scale, The earth is perfectly round and perfectly smooth!!

II. The Size of the Earth Eratosthenes was a Greek mathematician. He was the first person to determine the circumference of the earth. He did this 2,000 years ago!

His method of determining the circumference of a circle is still used today. Comparing the value he calculated to the known circumference of the earth, Eratosthenes only had a 0.9% error! Wow!!!

III. Parts of the Earth A. The Lithosphere The solid portion of the earth’s surface Refers to the rock layer that forms a fragmented shell around the earth

The lithosphere continues beneath the oceans. The uppermost layer is called the crust. There are two types of crust: Oceanic and Continental See ESRT page 10 for inferred properties of the earth’s interior.

B. Hydrosphere This includes all of the water in, on, and around the earth. ~70% of the surface of the earth is covered by water When compared to the size of the earth, the oceans are insignificant and cannot be drawn to scale.

C. The Atmosphere Includes all of the gases that surround the earth. See ESRT page 14 for selected properties of the earth’s atmosphere

See ESRT page 11 for average composition of the earth’s lithosphere, hydrosphere and atmosphere.

IV. Locating Positions on the Earth Because the earth is a sphere, we use a coordinate system to precisely locate positions on the earth. This system assigns two numbers to every point on the earth.

This system operates like a graph with horizontal and vertical values. Like any graph, the horizontal value is stated first!

A. Latitude Latitude is the horizontal value The reference line of latitude is the equator. The latitude of the equator is 0º Latitude is the angular distance measured north or south of the equator.

1. Measuring latitude in the Northern Hemisphere: Latitude is equal to the altitude to Polaris (North Star) In Rochester, the altitude to Polaris is ~43º … what is our latitude?

B. Longitude Longitude is the vertical value. The reference line for longitude is the Prime Meridian and is 0º and runs from the north to the south pole.

The International Dateline is 180º from the Prime Meridian on the “opposite” side of the earth. Longitude is the angular distance measured east or west of the Prime Meridian.

1. Measuring Longitude Longitude is based upon the differences in solar time from one location to another. Solar time is time based upon the position of the sun in the sky.

The sun appears to travel through our sky in a path that is an arc. When the sun is at its highest point in its path, the time is said to be solar noon.

The sun appears to travel through our sky 360º in 24 hours This equals a rate of 15º/hour

When the solar time of two locations and the longitude of one location are known, the new longitude can be determined.

If solar time is earlier at the new location, you have traveled west. If solar time is later at the new location, you have traveled east.

For example: It is 8:00 a.m. at one location and 12:00 p.m. at another. How many degrees of longitude separate the two locations?

Determine the time difference: 4 hours difference Set up the proportion: 15º = x 1 hr 4 hrs X = 60º The first location is west of the second because it is earlier.

Now you try! You have traveled so that your solar time is 2:00 p.m. and your home solar time is 7:00 a.m. How far have you traveled and in what direction?

Degrees of latitude and longitude are divided into smaller components called minutes (60 minutes = 1 degree) 15’ is equal to ¼ of a degree 30’ is equal to ½ of a degree 45’ is equal to ¾ of a degree

Determine latitude and longitude Polaris is 25º above the horizon. Local solar noon occurs at 11:00 GMT Polaris is now 20º above the horizon. Local solar noon now occurs at 9:00 GMT

Latitude is written first, followed by the N/S direction Longitude is next followed by the E/W direction

Now you try! Using your ESRT, find the latitude and longitude of: Rochester Elmira Watertown

V. Describing Earth’s Fields A. Fields A field is a region of space in which there is a measurable quantity of a given property at every point. A field is the location in which data is gathered.

The field value is the quantity (property) being measured. Examples of field values: Air pressure Temperature Elevation Precipitation

B. Field Maps visual representation of the readings within a given field. They are created to provide a greater understanding of the data.

C. Isolines lines that connect points of equal value on a field map.

Specific isolines and the field value they connect. Isobars…barometric pressure Isotherms…temperature Contour lines…elevation

Lines may never cross Lines may never touch Lines must make numerical sense Lines must make concentric circles or begin and end off the map When drawing isolines:

D.Analyzing Field Maps 1. Slope/Gradient We can visually estimate the amount that the field value changes by looking at the spacing between the isolines.

If the lines are: close together, the field value is changing rapidly…the slope is steep. far apart, the field value is changing slowly…the slope is gentle.

We can mathematically determine the amount of change by calculating the gradient between two points on a field map. Gradient = Δ in field value distance

2. Stream Flow By analyzing the contour lines, we can determine the direction a stream flows. Contour lines bend towards areas of higher elevation Therefore: Contour lines bend upstream

3. Depressions Indicated by hachure marks on contour lines. The first depression contour is equal in value to the last elevational contour. The values continue downward by the existing contour interval.

4. Drawing a Profile Identify the profile line Mark each contour line on the edge of a separate piece of paper Create the side view using the exact spacing of your marks Be sure to “bump” up or down

Now you try! Draw 5 concentric circles Label each line (create a contour interval) Identify a line to profile Draw your profile.

5. Estimating Elevation When asked to approximate elevation, you must determine the elevation of the two adjacent contour lines The estimated value must be between them

a. Highest possible elevation Last contour line is 700 m If there was a next contour line, it would be 800 m The highest possible elevation of point A is 799 m A 500 Contour interval = 100 m

b. Lowest possible elevation Last contour line is 100 m Next contour line would be 80 m Lowest possible elevation would be 81 m A Contour interval = 20 m 100