Pluto and Changing Astronomy

Five years ago, the Milky Way galaxy held nine planets.  Then, the comparison of dwarf planet Eris to previous title holder of ‘Ninth Planet’, Pluto, forced a change that would cause textbooks worldwide to be rewritten and transform the way we defined planets forever.  In 2006, astronomists from all over Earth came together to determine a universal rule by which planets could be identified.

The decided the following:

• A planet orbits a sun
• A planet has enough gravity to pull itself into a spherical shape
• A planet must be the dominant gravitational body in its orbit

Pluto passes the first two tests, but within its far-flung orbit, known now as the Kuiper Belt, there exist many other objects of similar size or mass, including Eris, a round icy object larger and more massive than the previous ninth planet.  With these definitions in place, it became clear that Pluto no longer made the cut.  It, Eris, and several other bodies in the Kuiper Belt are now known as dwarf planets.

Every book on astronomy which endeavored to remain current had to be rewritten, which was no simple task.  Our own Astronomy For Beginners was no exception, and shortly after Pluto’s reclassification, a new version was published.  It just goes to show that nothing lasts forever.  Sorry, Pluto!

Today in History: 1980 -- Voyager I takes the first pictures of Saturn's rings

On November 12, 1980, Voyager I, a NASA space probe launched on September 5, 1977, made its closest approach to Saturn and captured the first up-close images of Saturn's rings. Voyager I was launched with the purpose of visiting Jupiter and Saturn and giving us a better look at the largest planets in our solar system (and their moons). Saturn's rings are not visible from Earth with the naked eye and were first seen through a telescope by Galileo Galilei, in 1610, almost 370 years before the Voyager I.

To this day, Voyager 1 continues to send information back to Earth and, 30 years after its closest approach to Saturn, the space probe is located a mere 10.712 billion miles, only .2% of a single lightyear, from the sun.

For more information on Saturn's majestic, particle-based rings, pick up a copy of Astronomy For Beginners.

A collage of images of Saturn and its satellites taken by Voyage I on November 12, 1980

Today in History: 1995 -- Comet Hale-Bopp is Discovered

On this day, July 23, in 1995, astronomers Alan Hale and Thomas Bopp discovered Comet Hale-Bopp. The comet became visible to the naked eye one year after its discovery, increasing in brightness through late 1996 and into 1997. It is arguably the most widely observed comet of the twentieth century and one of the brightest seen in decades. It was visible to the naked eye for 18 months and came to be known as the Great Comet of 1997.

Read more about comets in Astronomy For Beginners, our graphic non-fiction title that answers many mysteries of the universe in terms that are readable and fun.