Daily Insolation& The Sun’s Path

Duration of Insolation

• Measure of the number of daylight hours

• Varies with seasons and latitude• The longer the period of daylight,

the warmer temperatures you will experience for your latitude

• Season:– most daylight on June 21 “longest day of the year”

–least daylight hours on Dec. 21 “shortest day of the year”

• Latitude: –15 hours is max for NY

–24 hours is max at the poles

Sun’s Path looking south in the Northern Hemisphere

Daily Insolation

• Starts when the sun rises and increases throughout the morning

• Maximum at solar noon

• The rays become more indirect as the sun lowers in the sky and sets

Area of Illumination

900

900 Horizon

Max. & Min. Daily Temperature

• Hottest time of the day occurs some hours after solar noon

• Sunrise is the coldest time of day

• Angle of Insolation at lowest at sunrise and sunset

This is not some Victorian watercolor, but a brand new six month pinhole camera exposure by English photographer Justin Quinell, showing the daily path of the sun over the Avon bridge. the interruptions and missing arcs are due to passing  clouds and days of rain or overcast.

Apparent Daily Motion of the Sun

Sun’s altitude changes 23.50 per season

Facts to Remember:

In NYS:

•An observer must always look south to see the sun at noon

•The Sun will never be overhead

• Path of the Sun

• Custom Sun Path

• Sunshine & Seasons 1.  Solar Motions     *  Daily:  east to west relative to horizon     *  Annual:  eastward, relative to stars     *  Angular diameter of sun (0.5o) 2.  Equinoxes & Solstices     *  Equinoxes:  intersections of equator & ecliptic         >  Mar 21, Sep 23     *  Solstices:  maximum separation from equator         >  Jun 21, Dec 21 3.  Rising, Setting & Solar Noon     *  Rising/setting points vary through the year     *  Noon altitude varies     *  Duration of daylight varies     *  Variations result from change in orientation of Earth             relative to sun 4.  Reasons for the Seasons     *  Temperature varies with season

    *  Temperature variation unrelated to Earth-sun distance variation.