Astronomers believe that galaxies have spiral arms - in part - because galaxies rotate, or spin around, a central axis.

There are still mysteries in astronomy, says Eric Mamajek. He talks about a surprisingly hot object 170 million light years from Earth that could be the result of a collision between two distant planets.

How many stars in the Milky Way? The estimate for the number of stars in the Milky Way is about 100 billion stars - plus or minus 50 billion.

Hear Katrina Exter on solving the puzzle of Shuster West 2, a glowing ring of ionized gases 4,000 light-years away. Read about the bizarre star trio.

Astronomers estimate that the luminosity of the Milky Way’s “core” is equal to about 10 million suns. Read more about interstellar dust here.

Light from Earth becomes too faint to see with the eye alone at around 14 billion kilometers (about 9 billion miles) from our home planet.

NASA has announced plans to return to the moon and establish a human presence there. Read more about the inflatable lunar habitat being developed.

12 o'clock a.m. and 12 o'clock p.m. mean different things to different people across the world. It's better to say noon or midnight.

Astronomer Michael Liu talks about the most lightweight stellar objects found outside our solar system. It's a pair of brown dwarfs, sometimes called 'failed stars' because they lack enough mass to sustain the nuclear reactions that let stars like our sun light up.

August 1, 2008. Today is an eclipse day - a total solar eclipse - where the moon's dark shadow sweeps across Earth. EarthSky asked NASA senior astronomer Sten Odenwald of the Goddard Space Flight Center for more.