A little about our most frequent targets:
JUPITER The ﬁfth planet from the Sun, Jupiter is the most massive planet
in our solar system, and in composition it resembles a small star. In fact,
if Jupiter had been between ﬁfty and one hundred times more massive, itwould have become a star rather than a planet. One of the most prominent
visible features of Jupiter is the Great Red Spot, a massive storm that has
raged for more than 300 years and is nearly the size of three Earths.
To date, 63 moons have been discovered orbiting Jupiter — the four largest are easily visible in a small telescope. Ganymede is the largest planetary
moon and has its own magnetic ﬁeld. Liquid oceans may lie beneath thecrusts of Europa and Callisto. Io has hundreds of active volcanoes.

http://otastro.org
We stop people on sidewalks and show them the craters of
the Moon, the moons of Jupiter, the rings of Saturn, or thespots on the Sun. For just a moment, they have a personalconnection to the universe around them, and sometimes life
seems a little better after that.
We call it “urban guerilla astronomy.”
The Sidewalk Astronomers was founded in 1968 in San
Francisco by John Dobson. You can ﬁnd more information
about the Sidewalk Astronomers, our observing plans,and current astronomical information on the Old Town
Astronomers web page, http://otastro.org. We have an email
announcement list to let you know about sidewalk and otherastronomy events in the LA area.
Our group most often sets up telescopes in old town
Pasadena on Colorado Blvd. near Delacey, and in old town
Monrovia at Myrtle and Lime. Our events are subject to clear
skies; we will notify our email list with updates. If you would
like us to visit your school or community group, please email
for help with the astronomical calendar. OTSA is part of theSidewalk Astronomers, and the JPL Saturn Observation
Campaign. Telescope viewing is always free of charge.
Founded by Morris “Mojo” Jones and Jane Houston Jones
Monrovia, CA (626) 359-5323
Information email: sidewalk@otastro.com web: http://otastro.org• Distance at opposition (closest): 365 million miles• Orbital period (its year): 12 years• Diameter: 89,700 miles
SATURN, the sixth planet from the Sun, is the most distant of the ﬁve planets known to ancient stargazers. In 1611, Italian Galileo Galilei was the ﬁrst
astronomer to gaze at Saturn through a telescope. Like Jupiter, Uranus, andNeptune, Saturn is a gas giant. It is made mostly of helium and hydrogen.
Saturn’s ring system is the most extensive and complex in our solar system;
including the faint E ring, it extends nearly 300,000 miles from the planet.
In fact, Saturn and its main rings would just ﬁt in the distance between Earthand the Moon.
In 2004 the Cassini-Huygens spacecraft arrived at Saturn and began studying the planet and its largest moon, Titan. Titan is the second-largest moonin the Solar System and believed to have an atmosphere similar to Earth’s
long ago. To date, Saturn is known to have at least 61 moons, of which 52
have been named.
• Distance at opposition (closest): 746 million miles• Orbital period (its year): 29.5 years• Diameter (excluding rings): 74,500 miles
MOON Earth’s only natural satellite is smaller than four other moons in thesolar system, yet it is larger than Pluto. More than 70 spacecraft have been
sent to the Moon and 12 astronauts have walked upon its surface. The presence of the Moon stabilizes Earth’s wobble. Over billions of years, the Earth’s
stable spin made for a stable climate that may have inﬂuenced the development and growth of life here.
From Earth, we see the same face of the Moon all the time because the Moon
rotates just once on its own axis in very nearly the same time that it travels
once around Earth. This is known as “synchronous rotation.” Many othermoons in the solar system have similar synchronous rotation, and are said tobe “tidally locked.”• Distance: 239,000 miles• Time between full moons (or new moons): 29.5 days
• Diameter: 2,159 miles
For more information about the solar system, visit The Nine Planets Website
at http://nineplanets.org.