Which famous galaxy in the night sky is named after a princess from Greek mythology?

Introduction / Context:
Astronomy is full of names borrowed from mythology and ancient cultures. Many stars, constellations and galaxies are named after characters from Greek myths. The Andromeda Galaxy is one of the most famous galaxies visible to the naked eye and provides a good example of this naming tradition. This question checks your ability to link that galaxy with its mythological origin.

Given Data / Assumptions:

• Some galaxies are named after figures from Greek mythology.
• Andromeda is a princess in Greek myth who was rescued by Perseus.
• The names Whirlpool, Messier and Cygnus have different origins or uses in astronomy.

Concept / Approach:
The Andromeda Galaxy, also known as M31, is a spiral galaxy that is the nearest large galaxy to the Milky Way. It takes its name from the constellation Andromeda, which itself is named after the mythological princess Andromeda. She was chained to a rock as a sacrifice to a sea monster and later rescued by the hero Perseus. The Whirlpool Galaxy is a separate object whose name describes its spiral appearance. Cygnus is a constellation whose name means swan, and Messier refers to a catalogue of objects rather than a single princess.

Step-by-Step Solution:
Step 1: Recall that Andromeda is both a constellation and the name of a nearby spiral galaxy. Step 2: Remember that Andromeda in Greek mythology is a princess. Step 3: Note that the Whirlpool Galaxy is named for its whirlpool like shape, not a mythological princess. Step 4: Recognise that Messier is a catalogue name and Cygnus is a swan constellation, not a princess. Step 5: Conclude that the galaxy named after a Greek princess is Andromeda.

Verification / Alternative check:
Astronomy references commonly describe the Andromeda Galaxy as part of the Local Group of galaxies and mention its mythological origin. Planetarium shows, school textbooks and sky maps all link Andromeda with the story of Perseus and the sea monster. No similar princess story is attached to the Whirlpool, Messier label or Cygnus in this context.

Why Other Options Are Wrong:
Option b, Whirlpool, describes the visual pattern of the galaxy M51 but is not a mythological princess.

Option c, Messier, refers to the French astronomer Charles Messier and his catalogue of deep sky objects.

Option d, Cygnus, means swan and is the name of a constellation and region of the sky, not a princess.

Common Pitfalls:
Students sometimes confuse constellation names and galaxy names, especially because both can share a word. Another pitfall is thinking that any poetic name like Whirlpool might be linked to myth, when it may simply describe appearance. Linking each word to its story, such as Andromeda the princess, helps keep these names organised in memory.

Final Answer:
The galaxy named after a Greek princess is the Andromeda Galaxy.