東方とうほうの空そらに輝かがやく「クリスマスの星ほし」──木星もくせいの最接近さいせっきんがもたらす夜空よぞらの神秘しんぴ

This month, in the Northern Hemisphere, if you look up at the eastern sky two to three hours after midnight, you can see a single point of light shining much brighter than the other stars.

Thats Jupiter. And as the period called opposition, when Jupiter shines brightest, will occur in early January next year, the time Jupiter appears in the sky is getting earlier and earlier.

At the end of this month in particular, Jupiter will become very prominent, to the extent that it is likened to the Star of Bethlehem that appears in the story of the birth of Jesus Christ.

Currently, Jupiter is located in Gemini and is shining very brightly at magnitude -2.6.

It has reached almost its maximum brightness and is brighter than any star in the night sky.

In Honshu, Japan, Jupiter appears above the northeastern horizon around 7:30 to 8:00 p.m., and then gradually rises higher into the southeastern sky.

Around 9 p.m., the bright light becomes clearly visible to everyone, and nearby, the two bright stars of Gemini, Castor second magnitude and Pollux first magnitude, are also shining.

The legend of the bright star that appeared at the birth of Jesus Christ is recorded in the Gospel of Matthew, chapter 2, verses 1 to 12 of the New Testament, where it is said that three wise men from the East were guided by this star to meet Jesus and offered him gold, frankincense, and myrrh.

On this occasion, countries with Christian faith celebrate Epiphany on January 6th.

So, why does Jupiter appear especially bright this Christmas?

The reason is not because Jupiters brightness changes, but because the Earth orbits the Sun much faster than Jupiter, so the distance between the two planets changes.

Professor Tom Stallard of Northumbria University Department of Planetary Astronomy explains, The reason Jupiter will appear brightest in the night sky this December is because this is the time of year when it comes closest to Earth.

Outer planets like Jupiter come closest to Earth when they are at opposition, meaning they are on the opposite side of the Sun with Earth in between. At this time, Jupiter appears brightest when viewed from Earth.

The next opposition of Jupiter will occur on January 10, 2026.

Jupiters orbital period is about 12 years, which is much longer than Earths, so while Earth completes one revolution around the Sun in a year, Jupiter only travels 1/12 of its orbit.

Professor Stallard says, Jupiters opposition, that is, the time when it comes closest to Earth, occurs about once every 13 months, and each time it happens about a month later than the previous one.

When the distance increases, the light spreads out and the brightness that reaches our eyes decreases, so Jupiter appears dimmer the farther it moves away from Earth.

Could it be that the Star of Bethlehem was actually Jupiter?

Considering Jupiters 13-month opposition cycle and the fact that its position changes daily, astronomically speaking, the possibility of Jupiter being the Star of Bethlehem is almost entirely ruled out.

Professor Stallard also pointed out that the brightness of Jupiter in December this year does not match the phenomenon known as the Star of Bethlehem, and stated that astronomers at the time were well aware of Jupiters position and brightness, so they probably would not have been surprised by a slight change in brightness.

Regarding the hypotheses about the Star of Christmas, there are many opinions that it could have been the sudden appearance of a comet or a supernova, or the phenomenon known as a Great Conjunction, in which Jupiter and Saturn appear very close together as seen from Earth.

In 7 BCE, three conjunctions of Jupiter and Saturn were recorded, and this hypothesis was proposed in the 17th century by the astronomer Johannes Kepler.

Another candidate is Sirius, the brightest star in the constellation Canis Major.

Sirius is a binary star system located 8.6 light-years from the Sun, and is famous as the brightest star in the night sky.

This month, Sirius rises about four hours after sunset and, with a brightness of -1.4 magnitude, outshines the other stars in the constellation Orion.

The reason Sirius appears to twinkle with a bluish-white light is because it is close to Earth and, when observed from the mid-latitudes of the Northern Hemisphere, it is low in the sky, making it more susceptible to atmospheric turbulence.

As you can see, there are many astronomical hypotheses regarding the phenomenon known as the Christmas Star, but there is still no definitive evidence.

However, the prominent brilliance of Jupiter in this months night sky shows that the legends of the stars have sparked peoples imaginations since ancient times and continue to captivate our hearts even today.