Unit 5 : Activity 5 : Latitude and Climate : Reason for the Seasons : Seasonal Delay : Reference Page : Unit Exam

Unit 1: How to Point to a Star
Unit 2: Where on Earth Are You?
Unit 3: Earth's Rotation and the Sun's Apparent Motion
Unit 4: Yearly Changes in the Sky
Unit 5: Seasons and Climate
Unit 6: Sundials
Unit 7: Navigation
Unit 8: Ancient Astronomy
Unit 9: Constellations

Latitude and Climate

One of the most important factors determining your climate is your latitude.  Between 23.5S and 23.5N latitude we have the tropics - where high temperatures are the norm, and the sun can beat down from directly overhead once or twice each year.  From 23.5N to 66.5N and between 23.5S and 66.5S are the temperate zones, where there are clear spring/summer/fall/winter seasons.  From 66.5N to the North Pole we have the Arctic, and from 66.5S to the South Pole, the Antarctic.  In these arctic zones the sun is above the horizon at midnight for part or all of the summer and never rises at all during some day(s) in the winter.  At the pole, daily motion is parallel to the horizon.

With the meridian diagram, we can find out the altitude of the sun at noon at any season as observed from any place on Earth.  This information can be very helpful in planning a garden or a house so that the sun will shine on the areas we want it to.  Knowing the sun's altitude at noon in the summer is also useful in figuring out how to shade your windows against the noon summer sun, while allowing the winter sun to shine in and keep you warm in the interior. The following meridian diagram is sketched for Ames, Iowa latitude of 42 degrees N.

Interactive Graphic 5-1-1
Click the Play button at the bottom right.

1) In the interactive graphic above, the angle between the arrow pointing to the celestial equator and the arrow pointing to the Sun is what at the summer solstice?

Equal to 90 deg minus the latitude of the observer
Minus the tilt of Earth's axis, or -23.5 degrees
Equal to the tilt of Earth's axis, or 23.5 deg

Just as in Question 5-1-1 above, at the winter solstice, the angle between the arrow pointing to the sun and the arrow pointing to the celestial equator in the interactive graphic above is equal to the tilt of Earth's axis, 23.5 degrees.  The tilt of the Earth's axis results in an apparent annual motion of the sun from -23.5 deg in December to +23.5 deg in June, on the date of the summer solstice.

Thus, the altitude of the sun at noon in Ames at the winter solstice is 48 degrees minus 23.5 degrees = 24.5 degrees.  This is true because the celestial equator is at 90 minus the local latitude = 90 - 42 = 48 deg altitude, as seen from Ames.  At the winter solstice, the sun is 23.5 degrees S. of the CE, so the sun is lower in the sky by 23.5 degrees, which means it reaches an altitude of 24.5 degrees.

2) At the summer solstice the sun transits the meridian in Ames, Iowa at what altitude?

90 + 23.5 = 113.5 deg
90 - 23.5 = 66.5 deg
48+23.5 = 71.5 deg

Climate Zones

Latitudes between 23.55 and 23.5 N are called the Tropics.  Latitudes between 23.5 and 66.5 N or S are the Temperate Zones and between 66.5 and 90 N or S are the Arctic (and Antarctic) zones.

3) North of 66.5 N latitude, in the Arctic, there is sunshine for how many hours per day at midsummer?

12 Hours
24 Hours
No Hours

4) North of 66.5 N latitude, in the Arctic, how many hours of sunshine are there in mid-winter?

12 Hours
24 Hours
No Hours

5) Between 23.5 N and 23.5 S latitude it is possible for the sun to pass through what special point?

Hint: this is something that can not happen in Ames, Iowa.

The Zenith
The Ecliptic Pole
The North Celestial Pole

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