Why is the planet Mars red?
“Because it’s rusty.”
Astronomy hobbyist Christine Moulen (standing, above) was helping Slava Arabagi of Brighton to get a look through one of five telescopes set up in front of City Hall last night. Her telescope was trained on Mars.
Iron oxide is plentiful in the soil of the planet, Moulen explained. The rust color helps us to identify Mars in the night sky.
Moulen is a member of the Amateur Telescope Makers of Boston, Inc., a.k.a. ATMoB. The organization hosted the viewing event titled Urban Astronomy on Friday evening, April 20, which was Day 1 of the 10-day Cambridge Science Festival.
Slava Arabagi was one of some forty adults and kids lined up around the instruments at about 10 p.m. The City Hall lawn was one of ATMoB’s two viewing stations; the other was at Harvard Square.
Mars, the planet Arabagi is looking at, was named by the Romans after their god of war because of its ruddy color, as described in Shakespeare’s Henry IV: “The mailèd Mars shall on his altar sit/ Up to the ears in blood.”
Viewing conditions Friday night were unusually good for this urban area, with heavenly bodies showing up well despite some haze and occasional clouds. Viewers at other scopes exclaimed over Saturn’s rings; at least one of its many moons was also visible. At another station the sky-watchers marveled at Mizar, one of seven brilliant stars in the group we know as the Big Dipper. Mizar is the middle star in the “handle.” (The Big Dipper is also called the Drinking Gourd and the Plough, and it has other names in other cultures; it is part of the constellation Ursa Major, the Great Bear.)
Photo: the Big Dipper, by Nathan Wells, Creative Commons
Without a telescope, Mizar looks like a large single star to all but the sharpest eye. However, with the telescope Mizar appeared as two separate stars (Mizar plus a smaller neighbor, Alcor). In a further refinement, observers at the City Hall event said that the smaller of the two, Alcor, has been shown to be a binary system (i.e., a pair of stars orbiting around a common center of mass), while its bigger neighbor Mizar is actually made up of two binary systems. The three systems are thought to be gravitationally interconnected. Thus the Mizar-Alcor combination historically seen on star charts is in reality six interconnected stars.
The two stars at the front end of the Big Dipper bowl line up to point at the pole star (Polaris, or North Star) in the handle of the nearby Little Dipper. Polaris has been helping travelers in the northern hemisphere to get their bearings for millennia.
ATMoB was formed in 1934 with the cooperation of Dr. Harlow Shapley at Harvard College Observatory. The non-profit organization was joined in 1973 by the Bond Astronomical Society, whose name honored two earlier Harvard astronomers, William Cranch Bond and his son George Phillips Bond.
The club has regular meetings, open to the public, in Phillips Auditorium at the Harvard-Smithsonian Center for Astrophysics at 60 Garden Street. To view the sky away from city lights, members go to the ATMoB clubhouse on the grounds of MIT's Haystack Observatory in Westford, MA.