Galaxies

Galaxies

Oursun belonngs to a giant whirlpool of stars called the
millky way. Huge collections of stars are called galaxies, and like all
galaxies the milky is unimaginably vast. Galaxies come in  many owny galaxy, but others are fuzzy balls
or shapeless clouds.The smallest have just a few million stars. The largest
contain trillions. Although they look packed with  stars, galaxies are mostly empty space . If
you made a scale model of the milky way with a grain of sand for each star, the
nearest star to the Sun would be 6 km (4 miles) away. The furthest would be
130,000 km (80,000 miles) away. The stars in a galaxy are held together by
gravity   and travel slowly around the
galactic heart. In  many galaxies,
including ours,a supermassive blck hole lies 
hidden in the centre. Stars and other material  are sucked into this comic  plughole by 
gravity and disapper forever.

The Milky Way

If you could look down on the Milky Way galaxy from above,
the view would be like flying over a glittering city at night. Most of the
galaxy’s 200 billion  stars are in the
central buleg. Curving around this are two vast spiral arms and several smaller
arms.The Milky Way is thought to be a barred sprial (see panel),but we can’t
see its shape clearly from Earth as we view it from the inside. In the night
sky, the Milky Way appers only as a milky band of  light.

Galactic centre

This photo from an infrared (heat-sensitive) telescope shows
stars and gas clouds packin the centre of the 
Milky Way. A supermassive black hole lies hidden somewhere in this ares.

Solar System

Our Solar System is in a minor spiral arm called the Orion
Arm. We orbit the centre of the galaxy once every 200 million years, travelling
at about 200km (120 miles) a second.

Crab Nebula

Clouds of gas and dust occur throughout the Milky Way,
especially in the sprial arms.The Crab Nebula is a cloud of werckege left
behind by a dying star that exploded.

Globular cluster

Not all the Milky Wayn’s stars are in the main disc of the
galaxy. Many are  in globular clusters –tightly
 packed ball  of ancient stars floating above and  below the galaxy in a spherical region called
the halo

Galaxy shapes

Astronomers classife 
galaxies into just a few  main
types, depending on the shpe we observe from Earth. Spiral: A central hub of
stars is surrounded by spiral arms curving out. Elliptical : More than half of
all gelaxies are simple ball shapes. Barred spiral : A straight bar runs across
the centre, connecting sprial arms . Irregular :Galaies with no clear shape are
classified as irregular.