Name:____________________________________________ Date: ______________________
Class Exercise
Happy Equinox Day!
Sunday, March 20, 2022 at 15:33 UTC. (That's 11:33 a.m. Eastern Daylight Time.)
Full Moon: March 18, 2022, 3:15 a.m. Next Full Moon in 29½ days.
On March 21, 2022, Solar Noon is at 12:51 p.m.
March 2022
S
6
M
7
April 2022
T
W
T
F
S
1
2
3
4
5
8
9
10 11 12
S
3
M
4
T
5
W
6
T
7
F
S
1
2
8
9
13 14 15 16 17 18 19
10 11 12 13 14 15 16
20 21 22 23 24 25 26
17 18 19 20 21 22 23
27 28 29 30 31
24 25 26 27 28 29 30
We will measure the altitude (elevation angle, ) of the Sun on the Equinox and calculate the size of
the Earth using a method similar to Erastosthenes. At the Equator, on the Spring Equinox, the Sun is
seen on the zenith at local noon. Using the altitude of the Sun at noon in Boston, and the 4800 kilometer
distance from Boston to Quito, Ecuador (latitude 0°) we can calculate the size of the circumference of the
Earth
Two tools to measure the altitude of the Sun: a telescope and the shadow of a gnomon.
MEASUREMENTS AND CALCULATIONS:
TELESCOPE, elevation angle:
GNOMON,
Height, H
 = _______________
= _______________
Shadow length,
𝐻
𝛼 = tan−1 ( ) = ____________
𝐿
Calculate the average of  and
2
..............................................................
 = _______________
L = _______________
 2 = _______________
 = _______________
Calculate the Circumference of the Earth = ________________________
The date of Easter is determined to be the first Sunday after the first Full Moon after the Spring Equinox.
What date will Easter be this year? (Calculate, don’t google. Honor Code). ________________________