Zodiac constellation images. Constellations are identifiable groups of stars and zodiac constellations are those that lie on the ecliptic, the path of the Sun through the sky.
Division of the Ecliptic into Arcs
The ecliptic strip or belt in the celestial sphere (in whose confines the Sun’s describes a path) which is commonly divided into 360 degrees. The ecliptic is further divided into twelve arcs known in Middle Persian Zoroastrian texts as dwazdah-an "the twelve ones" each 30° long.

Each arc contains a named group of stars called a named constellation or group of prominent stars. The twelve constellations, dwazdah-akhtaran, together make up the Zoroastrian (and other) zodiac (Middle Persian, dwazdahan Modern Persian, زودیاک zudik). The constellation were seen as bayan, givers of beneficence while planets could portend harmful change or reduce the beneficence of the constellations.

Zodiac - Its Etymology
It is commonly understood that the term zodiac derives from Latin "zōdiacus" which means a circuit. One theory is that zodiacus derives from the Greek term ζῳδιακὸς κύκλος (zōdiakos kuklos), meaning "circle of animals", in turn derived from ζώδιον (zōdion), a small animal [ζῶον (zōon)] and zoion, living being. Another theory is that zodiacus derives from the Greek word "zoad" meaning the way or a step referring to the passage of the sun through these arc of the Zodiac.
The ecliptic belt containing the constellations that make up the Western Zodiac

Constellations & the Celestial Sphere
The Zodiac consists of twelve constellations, the Dwazdah-Akhtaran, a discernible group of stars that from a pattern.There are 88 constellations. The Greek poet Aratus of Soli (c. 315-c. 245 BCE) described 44 constellations in his Phaenomena. Ptolemy described 48 constellations in his Almagest, 47 of which are known today by their same names. Western representations of the constellations are similar to Iranian-Persian and Indian representations. Some Chinese representations are similar as well. Since the representations are imaginary, the similarities are more than coincidence.

Varak (Aries)
When the Zoroastrian zodiac was last assembled, the first degree of Varak the ram (known in the West as Aries) marked the start of vernal or spring equinox, the first day of spring in the northern hemisphere.

The Size of the Zodiac Sectors
According to the Greater Bundahishn (GB 2.6) the cosmos was fashioned in the semblance of a (solar) year and that each of "the twelve constellations, like twelve months, have thirty degrees just as every month has thirty days."

We note in our page on World Horoscope that the signs of the zodiac do not form 'houses' in themselves, but rather occupy 'houses' or sectors. Therefore, in the Zoroastrian zodiac, the size of the sectors or houses are fixed and do not vary with the size of the constellations that occupies it at a particular point in history. This is an important and critical difference in concept with other concepts of the zodiac.

In Western astrology, there are different ways of measuring the size of a sign of the zodiac, with some systems using the 30° rule while others adopt a variable size corresponding to the size of the associated constellation. As a group of stars, Aries fits within the sector boundaries of the 30° arc that defines the boundaries of its arc sector. While Aries and some other signs fit within the boundaries of their arcs, others like Pisces stretch beyond a 30° arc.

Time as in a calendar is defined and measured by the constellation occupying a sector at a point in time and by the position of the Sun in that 'house'.As such, the constellation of the zodiac is not the primary source of the properties of a sector or 'house'. Rather, they are a secondary source. The primary properties are defined by the name given to the sector and are constant. They are not subject to precession.

Twelve Signs of the Zodiac
In Zoroastrian astrology "each month belongs to a constellation" (GB 6B.2), and each constellation is represented as a sign of the zodiac. The twelve signs of the Zodiac used in Zoroastrian & Western astrology and their Gregorian calendar dates were (for the Age of Aries i.e. 2150 BCE-1 CE):
Gregorian Dates - Zoroastrian Calendar Zoroastrian Zodiac Names Western Zodiac Name Gregorian Dates
Mar 21-Apr 19 Varak/Warrag (lamb/ram). Aries Mar 21-Apr 18/20
Apr 20-May 19 Tora/Gav (bull/ox/cattle) Taurus Apr 19/21-May 20/21
May 20-Jun 18 Dopatkar/Do-pahikar (two figures/images) Gemini May 21/22-Jun 20/22
Jun 19-Jul 18 Kalakang/Karzang (crab) Cancer Jun 21/23-Jul 22/23
Jul 19-Aug 17 Ser/Shagr (lion) Leo Jul 23/24-Aug 22/23
Aug 18-Sep 16 Khusak/Hushag (ear of grain) Virgo Aug 23/24-Sep 22/23
Sep 17-Oct 16 Tarazuk/Taragug (balance/scales) Libra Sep 23/24-Oct 22/23
Oct 17-Nov 15 Gazdum (scorpion) Scorpio Oct 23/24-Nov 21/22
Nov 16-Dec 15 Nimasp/Nemasp (centaur) Sagittarius Nov 22/23-Dec 21/22
Dec 16-Jan 14 Vahik/Wahig (goat) Capricorn Dec 22/23-Jan 19/
Jan 15-Feb 13 Dul/Dol (water spout/pail) Aquarius Jan 20-Feb 18/19
Feb 14-Mar 15 Mahik/Mahig (fish) Pisces Feb 19/20-Mar 20
Mar 16-Mar 20 Hamaspath-maidyem (mid path of all) Pisces
For the Zoroastrian Zodiac names written in Old Persian cuneiform, please see the bottom of the page.
Classical depiction of the signs of the zodiac. The inner circle contains the hieroglyph of Hemphta, the triform and pantamorphic deity. In the six concentric bands surrounding the inner circle are (from within outward): (1) the numbers of the zodiacal houses in figures and also in words; (2) the modern names of the houses.(3) the Greek or the Egyptian names of the Egyptian deities assigned to the houses; (4) the complete figures of these deities; (5) the ancient or the modem zodiacal signs, sometimes both; (6) the number of decans or subdivisions of the houses.
Image and caption credit: Kircher’s Œdipus Ægyptiacus at the Living Prophecy.
Image below: Age of Pisces. Sun currently rises in the zodiac constellation Pisces on the vernal equinox, March 21. For current Age of Pisces associations, see our page Horoscope Qualities.
Vernal Equinox 2007 and constellations of the zodiac. Note the west to east order of the constellations. When the Sun rises in a particular constellation (here Pisces), it stays in that sign for the rest of the day and the entire constellation rotates east to west along with the Sun. We are currently in the Age of Pisces. Image credit: Covertress.

Zodiac Signs and the Zodiac Sectors of the Ecliptic
As we have noted above, since the constellations of the zodiac are of varying sizes, there are at times gaps between the constellations and at times they overlap. In addition, since the sectors of the ecliptic based on a month of 30 days is fixed at 30°, at times the constellations of the zodiac run over the boundaries of a sector and at times fit with space to spare.
The constellations and signs of the zodiac overlaid on a horoscope circle with twelve sectors of 30 degrees each.
Image credit: John Pratt.com
The signs of the zodiac. Image credit: Merriam-Webster

Triplicities / Trigons:
Earth, Water, Air and Fire
The twelves signs of the zodiac are divided into four triplicities/trigons, each made of three constellations separated from each other by 120 degrees.

Fire: Aries, Leo and Sagittarius
Earth: Taurus, Virgo, Sagittarius
Air: Gemini, Libra and Aquarius
Water Trigon: Cancer, Scorpio and Pisces

The Sun in a Sector Occupied by a Constellation of the Zodiac
More than 4,000 years ago, astronomers wondered how the sky would appear if the stars could be seen during the daytime. Based on their observations of the night sky, some astronomers determined that during the daytime, the Sun would appear to 'enter' or reside in a sector occupied by a different constellation each month. (This would be because the constellation would stay directly behind the Sun and as the earth continued to move along its orbit, the line of vision from the earth would see another constellation appear behind the Sun.)
Constellations of the zodiac along the ecliptic behind the Sun. Image credit: Encyclopedia of Science
However, we cannot directly observe this phenomenon since the brightness of the Sun hides all view of the constellations and their stars. However, the neighbouring constellations on both sides can be observed in a clear sky just before dawn and just after Sunset. From knowing the positions of the constellations during the night, it is possible to determine the position of the Sun in a particular constellation, or rather, the sector  occupied by a constellation each month.
Zodiac Constellation and a time map. Note anticlockwise progression of the constellations
but a clockwise progression of the years.
Image Credit; Drunken Astrology

Birth & Ascendant Sign
In Western astrology and horoscopes, a birth sign is the sign which the Sun occupied on a person's birthday. It is also called the Sun sign.

The ascendant or rising sign is the sign rising over the eastern horizon at the time of a person's birth. See the previous tab "Cosmos" for a more complete definition.

Zodiac names and symbols (in the circle belt), aspect names on the outside of the circle,
aspect signs and angles (inside of the circle)

Zodiac Names in Old Persian Cuneiform
Zodiac's Zoroastrian names in Old Persian cuneiform courtesy Fereydoun Rostam at fontspace.