From, http://www.scientificamerican.com/article.cfm?id=invisible-galaxy-crashing-into-milk-2009-11&sc=CAT_SPC_20091127
A giant invisible galaxy is colliding with our Milky Way, astronomers have discovered.
It is a vast cloud of hydrogen containing enough matter to make one hundred million suns - but has failed to produce any stars at all.
The presence of the dark blob was first detected last year. But only now has it been identified as a giant galaxy.
Calculations by astronomers at Sydney, Australia, show that the object, called Smith's Cloud, is 100 times bigger than thought.
The cosmic crash is not a threat to stars in our own bigger galaxy but its gravitational pull will distort the shape of the Milky Way over millions of years.
The astronomers says the invisible galaxy's trajectory suggests that it has already crashed through our galaxy's disk before, around 70 million years ago, New Scientist reports online.
For the Cenozoic period, which began about 70 million years ago and continues today, evidence derived from marine sediments provide a detailed, and fairly continuous, record for climate change. This record indicates decreasing deep-water temperature, along with the build-up of continental ice sheets. Much of this deep-water cooling occurred in three major steps about 36, 15 and 3 million years ago - the most recent of which continues today. During the present ice age, glaciers have advanced and retreated over 20 times, often blanketing North America with ice. Our climate today is actually a warm interval between these many periods of glaciation. The most recent period of glaciation, which many people think of as the "Ice Age", was at its height approximately 20,000 years ago.
Although the exact causes for ice ages, and the glacial cycles within them, have not been proven, they are most likely the result of a complicated dynamic interaction between such things as solar output, distance of the Earth from the sun, position and height of the continents, ocean circulation, and the composition of the atmosphere.
So what do you think is up with that?
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