Date: Wed, 11 May 2005 16:33:13 -0400 (EDT) Subject: Reasons for the Seasons BRIES - Topic VI "SEASONS," p. 69-70 [p. 69] The seasons are the four divisions of the year that are characterized by different types of weather conditions [winter, spring, summer, & fall]. For most of the Earth, the major difference in the seasons us the temperature. DIRECT CAUSE OF THE SEASONS. The [change of seasons is] the direct result of the cyclic variations in intensity- and duration of insolation that occur during the year. INDIRECT CAUSES OF THE SEASONS. The variations in insolation that cause the seasons are themselves the result of factors that may be called the indirect causes of the seasons. These indirect causes are the following: 1. Tilt of the Earth's axis. [p. 70] 2. Parallelism of the Earth's axis. 3. Revolution of the Earth [around the Sun]. SMALL EFFECT OF ELLIPTICAL ORBIT. The variation in [earth-Sun distance] is too small to have a significant effect on the seasons. For example, winter in the Northern Hemisphere occurs at a time when the Earth is actually nearest the Sun. *[graphic] Figure 6-10. Causes of the seasons. The tilt of the Earth's axis and parallelism of the axis result in varying angles- and duration of insolation through[out] the year. == Reasons-for-the-Seasons.xmbl Construct data table showing: - Day of Year (21st of ea. mo.) - Avg. High Temp (for 21st ea. mo.) - Angle of Insolation - Duration of Insolation [times SR & SS for 21st ea. mo., plus 01 JAN (Day 01) and DEC 31 (Day 365)] -- Day of Mo./Day of Yr. --------------------- JAN 01 Day 001 JAN 21 Day 021 JUL 21 Day 202 FEB 21 Day 052 AUG 21 Day 233 MAR 21 Day 080 SEP 21 Day 264 APR 21 Day 111 OCT 21 Day 294 MAY 21 Day 141 NOV 21 Day 325 JUN 21 Day 172 DEC 21 Day 355 DEC 31 Day 365 -- Average High Temp. ------------------ http://www.weather.com/activities/other/other/weather/ climo-monthly-graph.html?locid=22312 or alternate source, Bob Ryan's Weatherwise Guide & Almanac: Average High Temp. (degF) JAN 01 43 JAN 42 FEB 48 MAR 57 APR 68 MAY 77 JUN 85 JUL 89 AUG 86 SEP 78 OCT 66 NOV 55 DEC 45 DEC 31 44 Average Low Temp. (degF) JAN 01 29 JAN 27 FEB 31 MAR 39 APR 48 MAY 57 JUN 66 JUL 71 AUG 68 SEP 60 OCT 48 NOV 38 DEC 31 DEC 31 29 -- Angle of Insolation ------------------- http://aa.usno.navy.mil/data/docs/AltAz.html Altitude of Sun at Transit JAN 01 28.2 JUL 21 71.4 JAN 21 31.4 AUG 21 63.0 FEB 21 40.8 SEP 21 51.6 MAR 21 51.6 OCT 21 40.2 APR 21 63.2 NOV 21 31.1 MAY 21 71.4 DEC 21 27.7 JUN 21 74.6 DEC 31 28.1 -- Duration of Insolation ---------------------- SCSA Daylight Calculator http://www.wsanford.com/~wsanford/daylight/calculator.html WASHINGTON, DISTRICT OF COLUMBIA Rise and Set for the Sun for 2005 Eastern Standard Time Day (of mo.) 21 J 0722 1717 F 0651 1753 M 0610 1821 A 0523 1851 M 0451 1919 J 0443 1937 J 0500 1929 A 0527 1854 S 0555 1806 O 0624 1721 N 0658 1650 D 0723 1650 JAN 09h55m 9.92 JUL 14h29m 14.48 FEB 11h02m 11.03 AUG 13h27m 13.45 MAR 12h11m 12.18 SEP 12h11m 12.18 APR 13h28m 13.47 OCT 10h57m 10.95 MAY 14h28m 14.47 NOV 09h52m 9.87 JUN 14h54m 14.90 DEC 09h27m 9.45 JAN 01 SR = 07:26 SS = 04:56 DoI = 09h30m 9.50 DEC 31 SR = 07:27 SS = 04:56 DoI = 09h29m 9.48 == MATH-RELATED APPLICATIONS > RANGE = diff. betw. max. & min. values. What is the RANGE of ... http://www.mathgoodies.com/lessons/vol8/range.html "The range of a set of data is the difference between the highest and lowest values in the set. To find the range, first order the data from least to greatest. Then subtract the smallest value from the largest value in the set." ... avg. high temp.? 89 - 42 = 37degF ... angle of insolation? 74.6 - 27.7 = 46.9deg. ... duration of insolation? 14.90h - 9.45h = 5.45h -- > mean: average 42+45+48+55+57+66 | +68+77+78+85+86+89 = 796/12=66.3degF avg temp > median: middle number. List numbers in order: if there are an odd number of numbers in the data set, then find # in the middle; if there are an even number of numbers in the data set, then average the two middle numbers, e.g., 10 12 14 16, mode = 12+14 / 2 = 13. avg. of 66 & 68 = 67degF median temp > mode: most common number [Examine list to see which number occurs most frequently. If no number occurs more than once, then there is no mode. There may be bimodal- or trimodal number sets (two- or three numbers occur same number of times).] There is NO MODE for data set of avg. high temp., 21st ea. mo. == BSLG Reasons for the Seasons pp. 24-26 > Apply what you have learned: 3. (a) When it is summer in Virginia, what part of the world has winter? Why? (c) What is the effect of the combination of more direct sunlight and the length of day in the summer? 4. (a) Draw a diagram of the Sun, light rays, and Earth to show what it would look like if the Earth's axis had no tilt. (b) What do you think would be different about the seasons and the temperatures in Virginia if the Earth's axis were not tilted? == _Earth Science Investigations_ Inv. 18 [ellipses lab activity] 4. Table 18-1 lists observations of the apparent angular size of the Sun's diameter. These are recorded as semi-diameters [radii]. Plot a graph of semi-diameters vs. dates. [Y-axis numbered from 15' to 16', every block equals 5'.] Table 18-1 Observations of the Sun's Diameter (from the 1970 American Ephemeris and Nautical Almanac) Date Semi-diameter, minutes and seconds of arc Jan 1 16'17.49" Jun 30 15'44.41" Jan 20 16'16.82" Jul 20 15'45.91" Feb 10 16'14.00" Aug 10 15'48.21" Mar 1 16'10.05" Aug 30 15'51.93" Mar 20 16'05.14" Sep 20 15'57.10" Apr 10 15'59.38" Oct 10 16'02.55" Apr 30 15'54.18" Oct 30 16'07.90" May 20 15'49.88" Nov 20 16'12.80" Jun 10 15'46.72" Dec 10 16'16.07" 5. On which date does the Sun appear to be largest? Smallest? Average in size? 6. Why does the Sun seem to change in diameter? 7. The position on the orbit closest to the Sun is known as perihelion. The farthest is called aphelion. [On your graph, label perihelion and aphelion.] ================================================================= Walter Sanford, Director Carl Sandburg Middle School Center for Sky Awareness 8428 Fort Hunt Road Sandburg Planetarium Alexandria, VA 22308 Fairfax County Public Schools Work: 703-799-6169 -6197 (fax) E-mail: wsanford@wsanford.com Home: 703-765-9392 AMS Project ATMOSPHERE Atmospheric Education Resource Agent & Water in the Earth System (WES) Resource Teacher SCSA, Geosystems, & Camp T-Equity - URL: http://www.wsanford.com/ =================================================================