[7] It is believed to be a satellite of the Andromeda Galaxy or on its rebound into the latter due to their interactions, velocities,[8] and proximity to one another in the night sky.

[11] However, the SIMBAD Astronomical Database, a professional database, collates formal designations for astronomical objects and indicates that Pinwheel Galaxy refers to Messier 101,[12] which several amateur astronomy resources including public outreach websites identify by that name, and that is within the bounds of Ursa Major.

Its observability without optical aid ranges from being relatively easily seen by people using direct vision in deep rural locations under a dark, clear, transparent sky, to requiring use of averted vision by observers in locations beyond the suburbs in shallow rural areas under good viewing conditions.

Crumey has shown that although the total apparent V-magnitude of M33 is 5.72, it has an effective visual magnitude of approximately 6.6, meaning that a precondition for visibility is that the observer can see stars at least as faint as that latter figure.

In his work De systemate orbis cometici; deque admirandis coeli caracteribus ("About the systematics of the cometary orbit, and about the admirable objects of the sky"), he listed it as a cloud-like nebulosity or obscuration and gave the cryptic description, "near the Triangle hinc inde".

[20] When William Herschel compiled his extensive catalog of nebulae, he was careful not to include most of the objects identified by Messier.

It has a diameter measured through the D25 standard - the isophote where the surface brightness of the galaxy reaches 25 mag/arcsec2, to be about 18.74 kiloparsecs (61,100 light-years),[5] making it roughly 70% the size of the Milky Way.

The contribution of the dark matter component out to a radius of 55×10^3 ly (17 kpc) is equivalent to about 5 × 1010 solar masses.

[27][28] In the same year, the tip of the red-giant branch (TRGB) method was used to derive a distance estimate of 2,590×10^3 ± 80×10^3 ly (794 ± 25 kpc).

[8] In 2004, evidence was announced of a clumpy stream of hydrogen gas linking the Andromeda Galaxy with Triangulum, suggesting that the two may have tidally interacted in the past.

[34] The Pisces Dwarf (LGS 3), one of the small Local Group member galaxies, is located 2,022×10^3 ly (620 kpc) from the Sun.

The A is assigned when the galactic nucleus lacks a bar-shaped structure, in contrast to SB class barred spiral galaxies.

American astronomer Allan Sandage's "(s)" notation is used when the spiral arms emerge directly from the nucleus or central bar, rather than from an inner ring as with an (r)-type galaxy.

Finally, the cd suffix represents a stage along the spiral sequence that describes the openness of the arms.

[37] This galaxy has an inclination of 54° to the line of sight from Earth, allowing the structure to be examined without significant obstruction by gas and dust.

[41] Triangulum is classified as unbarred, but an analysis of the galaxy's shape shows what may be a weak bar-like structure about the galactic nucleus.

[46]) The total integrated rate of star formation in the Triangulum Galaxy is about 0.45 ± 0.1 solar masses per year.

[38][39] Based on analysis of the chemical composition of this galaxy, it appears to be divided into two distinct components with differing histories.

The inner disk within a radius of 30×10^3 ly (9 kpc) has a typical composition gradient that decreases linearly from the core.

[47] Using infrared observations from the Spitzer Space Telescope, a total of 515 discrete candidate sources of 24 μm emission within the Triangulum Galaxy have been catalogued as of 2007.

The brightest of these regions, NGC 604, may have undergone a discrete outburst of star formation about three million years ago.

[49] This nebula is the second most luminous HII region within the Local Group of galaxies, at (4.5 ± 1.5) × 107 times the luminosity of the Sun.

Similar asymmetries exist for H I and H II regions, plus highly luminous concentrations of massive, O type stars.

[53] In 2007, a black hole about 15.7 times the mass of the Sun was detected in this galaxy using data from the Chandra X-ray Observatory.

Suggested scenarios include being torn apart and absorbed by the greater companion, fueling the latter with hydrogen to form new stars; eventually exhausting all of its gas, and thus the ability to form new stars;[60] or participating in the collision between the Milky Way and M31, likely ending up orbiting the merger product and fusing with it much later.