S A Calculations

Total flux of radio astronomical sources

Assumptions

exclude the Sun
flux density averaged over the whole sky = 100 Jy
Total area of all radio telescopes ~ 1 sq km = 10⁶ sq meters.

Hence total energy received from all celestial radio sources per second

All radio telescopes: 100 * 10⁶* 10^-26 = 10^-18 Joule/sec
Over the whole Earth: 100 * A_Earth * 10^-26 = 5x10^-10 Joule/sec
(where: Surface area of the Earth A_Earth= 4pi *R_E² = 5.12x10¹⁴ sq meters.)
(Ave Radius of the Earth R_E = 6.38x10⁶ meters.)

Total Energy received per year

All Radio Telescopes : 3.2x10^-11 Joules
Whole Earth : 1.6x10^-2 Joules

Total Energy received Since 1932 (76 years)

All Radio Telescopes : 2.4x10^-9 Joules
Whole Earth : 1.2 Joules

Silly Comparisons

Energy required to melt a snowflake

Melting ice requires 80 calories per gram. (or 334 Joules/gram)
Hence 80 * 0.003 = 0.24 calories
1 calorie = 4.2 Joules
Hence energy to melt a snowflake ~ 1 Joule

Energy of a fly landing on the back of a deer

Assume fly drops in free-fall for 1 cm onto the deer.
Velocity of a falling object, v = gt
Distance fallen in time t, D = 0.5gt²
(where g=9.8m/s², and t is the elapsed time in sec)
so for D= 1 cm, then t = 0.045 second
and v = 0.44 m/s
The kinetic energy E = 0.5m_flyv²
and m_fly = 12x10^-6 kg
Hence E_fly = 1.2x10^-6 Joules.

Fact Reference

Mass of a common housefly = 10 mg www.fasebj.org/cgi/reprint/03-1464fjev1.pdf

Mass of a common housefly = 12 mg http://wiki.answers.com/Q/The_mass_of_a_housefly

typical mass of a snowflake = 3 mg http://hypertextbook.com/facts/2001/JudyMoy.shtml

Fact	Reference
Mass of a common housefly = 10 mg	www.fasebj.org/cgi/reprint/03-1464fjev1.pdf
Mass of a common housefly = 12 mg	http://wiki.answers.com/Q/The_mass_of_a_housefly
typical mass of a snowflake = 3 mg	http://hypertextbook.com/facts/2001/JudyMoy.shtml