Galaxies are massive gravitationally bound systems consisting of stars, gas, dust, and dark matter. They come in different shapes such as elliptical, spiral, and irregular. The word "galaxy" derives from the Greek word for the Milky Way galaxy, which was thought to have been formed from milk that sprayed from Hera's breast while she was nursing the infant Heracles. Major components of galaxies include stars, star clusters, interstellar gas and dust, supermassive black holes at their centers, and dark matter.

1. GALAXI
ES
ELLIPTICAL IRREGULAR
SPIRAL

2. GALAXY
• a massive gravitationally
bound system consisting of
stars, stellar remnants, an
interstellar medium of gas
and dust, and dark matter,
an important but poorly
understood component

3. • contain varying numbers of planets,
star systems, star clusters and types
of interstellar clouds. In between
these objects is a sparse interstellar
medium of gas, dust, and cosmic rays.
Supermassive black holes reside at
the center of most galaxies. They are
thought to be the primary driver of
active galactic nuclei found at the
core of some galaxies. The Milky
Way galaxy is known to harbor at
least one such object.

4. ETYMOLOGY
• The word galaxy derives
from the Greek term for our
own galaxy, galaxias
(γαλαξίας, "milky one"), or
kyklos ("circle") galaktikos
("milky") for its appearance
as a lighter colored band in
the sky.

5. GREEK
MYTHOLOGY• Zeus places his son born by a mortal
woman, the infant Heracles, on Hera's
breast while she is asleep so that the
baby will drink her divine milk and will
thus become immortal. Hera wakes up
while breastfeeding and then realizes she
is nursing an unknown baby: she pushes
the baby away and a jet of her milk
sprays the night sky, producing the faint
band of light known as the Milky Way.

6. SPIRALS
ELLIPTICALS
SPIRALS-b
Examples
of
Galaxies

7. ELLIPTICALS
has an ellipse-shaped light profile

8. SPIRALS
are disk-shaped with dusty, curving arms

9. SPIRALS-b

10. IRREGULARS
those with irregular or unusual shapes

11. IRREGULARS
are galactic formations that develop
unusual properties due to tidal
interactions with other galaxies

12. IRREGULARS
are galaxies that cannot be readily
classified into an elliptical or spiral