Melotte (Mel)

While the Messier catalog was built by a comet hunter and the NGC by visual astronomers, the Melotte Catalogue (Mel) was the first great census of star clusters created using the power of photography. It specializes in "open clusters"—groups of young stars born from the same cloud of gas.

History & Who Made It

The catalog was compiled by the British astronomer Philibert Jacques Melotte (1880–1961). It was published in 1915 in a paper titled A Catalogue of Star Clusters shown on Franklin-Adams Chart Plates.

John Franklin-Adams was an amateur astronomer who had spent years photographing the entire sky from both the Northern and Southern Hemispheres using high-quality lenses. Melotte, working at the Royal Observatory in Greenwich, was tasked with analyzing these photographic plates. Because he was looking at long-exposure photos rather than looking through a telescope with his own eyes, he could see faint, sprawling clusters that were invisible to earlier observers.

The Purpose: A Global Survey

The Melotte catalog was a major leap forward in astronomical record-keeping:

• • Completeness: It was one of the first catalogs to cover the entire sky (both North and South) with a consistent method.

  • Size and Scale: Melotte was particularly interested in "large" clusters. Many Melotte objects are so big that they don't look like clusters in a telescope; they only reveal their shape on wide-angle photographs.

  • Cataloging the Neighbors: Because Melotte used wide-field plates, he captured the clusters that are closest to Earth, which are often the most spread out across the sky.

What Objects and How Many

The catalog contains exactly 245 objects.

• • Open Clusters: 211 (The primary focus).

  • Globular Clusters: 34 (Dense, ancient balls of stars).

  • Double Clusters: Melotte was the first to formalize how many "paired" clusters existed in our local area.

Melotte Catalogue Highlights (Flat Text)

• Object 1: Melotte 22 (The Pleiades / M45) Constellation: Taurus Note: Perhaps the most famous star cluster in the world. It is a group of young, blue "sibling" stars.

• Object 2: Melotte 25 (The Hyades) Constellation: Taurus Note: The closest open cluster to our Solar System. It forms the distinct V-shape of the bull's face.

• Object 3: Melotte 111 (Coma Berenices Cluster) Constellation: Coma Berenices Note: A massive, loose cluster that covers a huge portion of the sky. It is best seen with the naked eye or binoculars.

• Object 4: Melotte 20 (Alpha Persei Cluster) Constellation: Perseus Note: A bright, sprawling group surrounding the star Mirfak.

• Object 5: Melotte 102 (The Southern Pleiades / Theta Carinae Cluster) Constellation: Carina Note: A brilliant southern hemisphere cluster that looks remarkably like the Northern Pleiades.

• Object 6: Melotte 15 Constellation: Cassiopeia Note: This cluster is located right at the heart of the "Heart Nebula" (IC 1805). It is the radiation from these stars that makes the nebula glow.

• Object 7: Melotte 186 Constellation: Ophiuchus Note: A very large, sparse cluster that is often ignored because its stars are so spread out.

The Observer's Guide: Use Your Binoculars

If you want to explore the Melotte catalog, put your telescope away. Because Melotte found these using wide-angle photographic plates, the objects are often too big for a telescope’s narrow field of view.

• Naked Eye: Many Melotte objects (like Mel 111 or Mel 25) are easily visible without any tools at all.

• Binoculars: This is the "sweet spot" for Melotte hunting. A standard 7x50 or 10x50 binocular will frame these clusters perfectly against the black of space.