Graphic Shows Size Of Rosetta's Comet/67P Churyumov-Gerasimenko

How's this for size? Shown above is the comet- 67P. Sometimes we cannot "gauge" the size of an object if there aren't any  other objects are in the same field of view. 

We previously posted an article on the Rosetta's Comet - 67P Churyumov-Gerasimenko. The Rosetta spacecraft has reached the Comet 67P Churyumov-Gerasimenko. 
Its purpose is to study how the nucleus is affected by the heat of the Sun. The spacecraft will orbit the comet as it heads toward the inner solar system.

The comet is headed toward the inner solar system as part of its 6.45-year-long orbit and is about 450 million kilometers (251 million miles) from Earth. 

Not to worry, the comet is no where near a possible collision with earth. If it was, we would be in big trouble. A comet of this size would wipe out the entire planet and possibly cause an orbital shift. Lastly, the comet would be much smaller in size and mass once it reached earth since it would have burned up upon passing through our atmosphere.
Happy comet hunting. "They" can use your help.