Astronomy and astrology are different. One difference … astrological signs of the tropical zodiac remain fixed relative to seasonal markers, such as the equinox and solstice points on the sky’s dome. Meanwhile, the constellations of the zodiac (and signs of the sidereal zodiac) slowly but surely shift eastward relative to the equinox and solstice points, over the long course of time, due to a motion of Earth called precession.
Also, signs of both the tropical and sidereal zodiac represent equal 30o divisions whereas the constellations of the zodiac vary in size.
In a celestial coordinate system commonly used by astronomers and astrologers, the sun resides at the First Point of Aries on the March equinox (0o of longitude on the ecliptic), irrespective of the fact that the sun shines in front of the constellation Pisces on the March equinox in our day and age.
We provide the dates for the sun’s entry into each sign of the tropical zodiac (and corresponding ecliptic longitude) for the year 2018.
Jan 20, 2018: Sun enters sign Aquarius (300o)
Feb 18, 2018: Sun enters sign Pisces (330o)
Mar 20, 2018: Sun enters sign Aries (0o)
April 20, 2018: Sun enters sign Taurus (30o)
May 21, 2018: Sun enters sign Gemini (60o)
June 21, 2018: Sun enters sign Cancer (90o)
July 22, 2018: Sun enters sign Leo (120o)
Aug 23, 2018: Sun enters sign Virgo (150o)
Sep 23, 2018: Sun enters sign Libra (180o)
Oct 23, 2018: Sun enters sign Scorpio (210o)
Nov 22, 2018: Sun enters sign Sagittarius (240o)
Dec 21, 2018: Sun enters sign Capricorn (270o)
Source: Timetable of astronomical events by Guy Ottewell
Want a quick comparison of these dates with the dates of the sun’s entry into astronomical constellations? Click here. Or check out the chart below, which Guy Ottewell posted to his blog in early 2016. Used with permission.
Bottom line: Dates for the sun’s entry into each sign of the zodiac (and corresponding ecliptic longitude) for the year 2018.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.