How can you recognize a comet from other celestial bodies?

Answer 1

The following would be seen during extended observations of a comet:

-- The object is not shown on charts or maps of the sky. It has appeared where

no permanent object was previously seen.,

-- Its proper motion is significant. It moves among the background "fixed" stars

from one night to the next.

-- Computation of its orbit based on several observations places it inside the

solar system, on a path that is either hyperbolic (open) or else elliptical with

large eccentricity, probably highly inclined to the ecliptic plane.

-- Computation of its orbit also indicates its distance. Once that's known,

and its brightness is measured, its size can be calculated, and it's found

to be very small ... like a few tens of miles in diameter.

-- As the object moves closer to the sun, it becomes brighter, which is to be

expected. But it also becomes larger and fuzzier, as if some surface material

is boiling off, enclosing the solid center in a large, wispy, fuzzy ball.

-- Eventually, the fuzzy envelope begins to elongate, grow away from the

center, and stream out away from the object appearing as a 'tail' or stream

of 'hair'. At first, the fuzz appears to drift off behind the object as the object

moves away from it. But as the path curves and the object eventually swings

around the sun and away from it, it's seen that the shape of the fuzzy envelope

and the 'tail' has nothing to do with the object's motion ... it simply always points

away from the sun, as if some kind of wind from the sun were blowing it away.

Answer 2

Comets typically have a fuzzy appearance due to the coma, or cloud of gas and dust, that surrounds them as they approach the Sun. They may also have a tail that points away from the Sun due to the solar wind. Comets move along predictable orbits, but can appear suddenly in the sky as they approach the inner Solar System.