A rare astronomical event will be visible in the sky tonight — the very close conjunction of Jupiter and Saturn, which is popularly being called the “Christmas Star.” And it just so happens to fall on the Winter Solstice.
Stargazers may have seen the two planets getting closer in the night sky, and tonight they’ll overlap just a tenth of a degree apart. Astronomers call this a “great conjunction.”
It has been 400 years since the planets overlapped so closely, and it’s been 800 years since it was visible in the night sky.
“Jupiter takes about 11.9 years to orbit the Sun, and Saturn takes about 29.5 years,” Chuck McPartlin, Santa Barbara Astronomical Unit outreach coordinator, said. “As a result, Saturn and Jupiter come into conjunction about every 19.6 years.
“What’s special about this conjunction is that they will be exceptionally close to each other and will appear to the unaided eye as a single bright object.”
The planets will be closest at 6 a.m., but it will be below Santa Barbara’s horizon. The conjunction will still be incredibly close throughout the night.
“That evening at sunset, the two gas giant planets will still be so close that a telescope at moderate magnification will show both planets and their brightest moons in the same field of view,” Mr. McPartlin said.
At sunset, around 4:53 p.m., the planets will be visible in the southwest at an altitude 22 degrees above the horizon, he said.
“If you want to wait for their next very close conjunction, it will be on March 15, 2080, but only briefly visible in the predawn sky,” he said.
The event can happen any time of year, and it’s purely coincidence that this conjunction occurs on the Winter Solstice for the northern hemisphere (which occurs at 2:02 a.m.).
While the planets seem to collide from a vantage point on Earth, they are hundreds of millions of miles apart in outer space.
Astronomers such as Johannes Kepler have hypothesized that a great conjunction could be The Star of Bethlehem, as described in the Gospel of Matthew. Kepler made this observation in 1604 after witnessing a conjunction.
While the validity of his hypothesis is unknown, it is a spectacular event to witness the week of Christmas and on the Winter Solstice.