Ambassador: Alkina, if I may, is this ship designed to observe distant objects?
Ambassador: Then perhaps we can see some more distant objects, perhaps something outside your solar system?
Alkina: How about something outside the galaxy?
Alkina: Epo, focus your instruments on the Whirlpool Galaxy!
Epo: I don’t recognize that name, please select a catalogue.
Alkina: Messier 51a.
Epo: Database Error: The Messier catalogue has not been loaded.
Alkina: What about the New General Catalogue?
Epo: That database is available.
Alkina: Then find NGC 5194.
Ambassador: I don’t think I am familiar with this, uh, whirlpool galaxy is it?
Alkina: Yes, it’s a spiral galaxy about 24 million lightyears away and 38,000 lightyears across.
Ambassador: Wondrous! And the smaller galaxy next to it?
Alkina: That’s NGC 5195, the dwarf galaxy M51a is interacting with.
What does it mean?
Catalogue – Since there are so many astronomical objects in the sky, the scientists who discover them organize them into catalogues. In many cases, the only name an astronomical object has is its catalogue number. Some objects appear in more than one catalogue and have more than one name.
Whirlpool Galaxy – Discovered by Charles Messier in 1773, the Whirlpool Galaxy is one of the most striking examples of a grand spiral formation.
Dwarf Galaxy – A galaxy that contains somewhere around several billion stars, as opposed to the hundreds of billions of stars found in a galaxy like our own.
In human speak please!
The famous French astronomer and comet hunter Charles Messier published the first edition of his catalogue in 1771 with 43 objects. It would eventually grow to include 103 objects by the time Messier had finished with it. Today it includes a total of 110 objects, including objects that Messier noticed, but never added to his list. Messier objects are usually abbreviated with the letter “M” followed by the object’s number.
The New General Catalogue was started in the 1880s using observations by astronomer William Herschel (famous for his discovery of Neptune). This catalogue has grown to contain nearly 8,000 astronomical objects. Unlike some catalogues, the NGC is not specific to a certain type of object (like galaxies or nebulas) but contains many types of objects.
Is that all?
April IYA Discovery Guide (PDF) – Learn more about M51a and how to spot it in the sky.
Whirlpool Galaxy – Wikipedia entry for the Whirlpool Galaxy.