Insolation and the Seasons What is Insolation Insolation

Insolation and the Seasons

What is Insolation? Insolation = INcoming SOLar radi. ATION!! Not to be confused with insulation, which is the stuff you put in your attic to keep your house warm in winter.

What is Insolation? l Energy received from the sun. It can be absorbed, reflected or reradiated.

Variations of Insolation The intensity of insolation received is not the same at every point on Earth. l The reasons for this are: l 1. Earth’s shape l 2. Latitude changes l 3. Seasonal changes l 4. Time of day l

Variations of Insolation l 1. Earth’s Shape l Earth is a sphere, not flat, therefore at any given time, there is just one place on Earth getting direct (90º) sunlight.

Variations of Insolation 2. Change in Latitude l The intensity of insolation is greatest at the equator, since it always gets direct (90º) rays of sunlight. l l With each degree in latitude you go up or down from the equator the intensity of insolation DECREASES.

Variation of Insolation l 3. Seasonal Changes l The angle of insolation changes as the Earth revolves around the sun during it’s 365. 24 day cycle.

Notice when the sun is lower in the sky you will have a longer shadow.

Variation of Insolation l 4. Time of Day l On any given day, the altitude (height) of the sun varies from zero (at sunrise) to a maximum (noon), back to zero again (at sunset).

By the way, wear sunscreen During the spring and summer months, the peak sun burning times are 10 am to 4 pm. l WHY? l

Variation of Insolation In addition to the angle of insolation changing, the duration of insolation changes as well. l The duration of insolation is the time between sunrise and sunset.

Seasons Video

Main Reason for the Seasons Main reason for the seasons: Earth is tilted on it’s axis 23. 5º

What Changes Do We Observe During The Seasons? 1. The sun’s altitude (height) changes with the seasons. l Highest = summer (June 21) l Lowest = winter (December 21) l NEVER directly overhead at our latitude!!

What Changes Do We Observe During Seasons? 2. Sunrise and Sunset positions change with the seasons. South of E/W in fall and winter North of E/W in spring and summer

Azimuth of sunrise changes with season North of East Dawn South of East

What Changes Do We Observe During Seasons? 3. Daylight length – Duration of Insolation Shortest on Winter Solstice, Dec. 21 12 hours on Equinox Longest on Summer Solstice, June 21.

Reasons for the seasons animation

The Summer Solstice l l l June 21 - longest daylight of the year. Sun at highest altitude at noon. 24 hrs of daylight at North Pole. Direct sun ray at 23° 30’ north latitude – also known as the Tropic of Cancer. Most likely to get sun burned. Sunrise = N of E, Sunset = N of W

The Winter Solstice l l l Dec. 21 - shortest daylight of the year. Sun at lowest altitude at noon. 24 hrs. of darkness at North Pole. Direct sun ray at 23° 30’ south latitude – also known as Tropic of Capricorn Not too much chance of sunburn, unless you ski. Sunrise = S of E , Sunset = S of W

The Equinoxes l l l Sept. 21 – Autumnal (Fall) Equinox March 21 - Vernal (Spring) Equinox 12 hrs of daylight, 12 hrs of night. The word equinox means equal day and equal night. Direct sun ray at Equator (0º) Sunrise = E, Sunset = W. This is also called Due East and Due West.

Realize that: June and July get approximately the same insolation l May and August get the same insolation l April and September get the same insolation. l l Wear Sunscreen.

Is Distance Important to Seasonal Change? Farthest away on July 4, 4 Closest on Jan. 3. NO! Earth’s orbit is an ellipse (oval).

Water with the appropriate temperature will only be found in tropical regions

What dates correspond to each figure? 2 1 – December 21, Winter Solstice 3 1 2 – March 21, Spring (vernal) Equinox 3 – June 21, Summer Solstice 4 4 – September 23, Fall (autumnal) Equinox