At today’s solstice (June 21, 2018 at 10:07 UTC), the sun was in front of the constellation Taurus the Bull. On June 21, 2018, at around 21:00 UTC, the sun moves out of the constellation Taurus and into the constellation Gemini the Twins. In other words, the sun on the June solstice shines very close to the Taurus-Gemini border.
Relative to the backdrop stars of the zodiac, the sun on the solstice always appears a tiny bit westward of the previous year’s solstice sun.
For instance, in the year 1989, the sun was in front of the constellation Gemini on the June solstice. Then one year later, in 1990, the June solstice sun was in front of the constellation Taurus, the constellation to the immediate west of Gemini. The sun on the June solstice will continue to shine in front of Taurus until the year 4609, when the June solstice sun will finally move into the constellation Aries, the constellation to the immediate west of Taurus.
Sign versus constellation
By definition, the sun occupies the first point of (the sign) Cancer on the June solstice, irrespective of which constellation backdrops the sun at this time. Also, the sun reaches the first point of (the sign) Leo when it resides 30 degrees east of the June solstice point along the ecliptic – irrespective of which constellation backdrops the sun.
Signs are fixed relative to the solstice and equinox points. On the other hand, the solstice and equinox points slowly but surely move westward relative to the zodiacal constellations.
The solstice and equinox points go full circle through the constellations of the zodiac in about 26,000 years.
Bottom line: On June 21, 2018, at around 21:00 UTC, the sun moves out of the constellation Taurus the Bull and into Gemini the Twins.
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.