Page 20 - Curriculum Visions Dynamic Book. To close the book, close the tab.

Filament
 Galaxy—Most galaxies form a spiral shape. This is NGC4414 as photographed by the Hubble Space Telescope.
F
Filament
A long strand of cool gas suspended in the Sun’s corona.
It looks like a dark line when
seen against the corona. It is the same as a prominence, except that a prominence appears beyond the corona. Because prominences are seen against the black of space, they appear bright, while the same strands of cool gas seen against the bright corona appear dark. They are connected to the Sun’s magnetic field.
Flare
A sudden eruption of energy on the solar disk, lasting minutes to hours. The Sun’s flares throw out massive amounts of particles, adding greatly to the solar wind.
Fluorescence
The glowing of a gas when its atoms have been excited by a source of radiation. The radiation may come from a hot star. The glow of a nebula is due to fluorescence.
Full Moon
The phase of the Moon when it lies in the opposite side of the sky from the Earth, and thus the full disk is illuminated.
Fusion
The process of two atoms joining together. Enormous amounts of energy are released when this happens. Part of this energy is seen in the light from the Sun and other stars.
20
G
Galaxy
A giant spiral made up of countless stars, gases, dust, and probably a few planets. It is all bound together by gravity in
the same way as the planets are bound to the Sun.
Galaxies are some of the most obvious features in the Universe. Some are small and contain fewer than a million stars. They are called dwarf galaxies. Others are huge and may contain thousands of millions of stars. They are called supergiants. The largest
are 600,000 light-years across, meaning that light would take this time just to get from one side to the other.
Galaxies have two shapes: either spiral, with arms, or ovals, without arms. The stars in the oval shapes are more evenly distributed.
Galaxies probably formed from rotating masses of gas early in
the life of the Universe. Galaxies do not remain the same, but continually change as the gas remaining in the galaxy condenses into new stars.
We can see the disk part of our galaxy as a shimmering band of stars in the clear night sky. We call this region the Milky Way. Some people use the term Milky Way to mean our whole galaxy.
Our galaxy, like others in the Universe, is mainly disk-shaped. The rotating disk is 100,000 light- years across and 1,000 light-years thick. The Sun is 26,000 light-years from the center of our galaxy on one of the outer spiral arms, known as the Orion arm.
Less conspicuous is a sphere surrounding the center. It contains old stars and makes up just under a third of the mass of the galaxy. All of these visible parts of the