A Christmas Comet

Just in time for the holidays Earth has a celestial visitor! Comet Wirtanen makes one of the closest approaches ever recorded. It’s a small comet with a short orbital period of 5-6 years. It is bright enough to see with the naked eye, although because of its small size the way it scatters light, it is hard to spot. Keeping with the holiday tradition, if you’re lucky enough to see it, it will appear to be green.

Wirtanen approaches, as seen in November (NASA)

I am sadly surrounded by street lights, so I had to take a short trip to a state park where I had a dark sky. With a spotting scope and a general area of where to look, I was unable to find Wirtanen. The comet makes its closest approach to the sun tonight, and I decided to try again. However, I’ve been blessed with clouds. My next chance is Saturday night, when it is closest to Earth. Of course, rain is in the forecast.

Geminids (Smithsonian Magazine)

While I failed in my attempt to see just my second comet, I happened to see a meteor streak across the sky. Meteor showers are bits of cometary debris burning up in the atmosphere as Earth passes through the comet’s debris field. Comets are just dirty snowballs that melt a little bit as they approach the sun. As they break up, all the pieces that break off trail behind and wait for our orbit to sweep them up. This meteor was not associated with Wirtanen. It was part of the Geminid meteor shower, which is debris from the comet 3200 Phaethon, a dead comet. Its ice has melted and all that remains is rock. Most likely, if we ever pick up all the debris then there will be no more Geminids.

If you want to try your luck at finding Wirtanen, here’s a handy link that shows its location throughout the month. This month's information is from StarDate and NASA.

Star of Wonder

Science is very good at explaining things and can even solve a mystery that has no remaining witnesses. Science is able to tell us how long ago a frozen cave man lived, and even how he died. One mystery that science has been unable to explain, but has offered many possible solutions to, is the Star of Bethlehem that the Magi followed. The star is mentioned in the gospels, and many biblical events have been confirmed by archaeology. But is the star a legend, a myth, a miracle, or something perfectly logical?

There are several astronomical phenomena that could explain the star. People at the time were very astute when it came to sky watching, as the stars and moon were (and still are) great navigational aids, so anything out of the ordinary appearing in the sky would have been noticed and documented. Some examples of astronomical phenomena that could have occurred on the First Noel include a planetary conjunction, a nova, a supernova, and a comet.

A planetary conjunction is when two or more planets appear very close to each other in the night sky, and may even appear to be a single object. Just such an event- a Jupiter and Saturn conjunction- took place in the year 7 BC, just outside the accepted date of Jesus’s birth (6 BC- 4 BC). The timing is very close and the position in the sky is correct, but the planets were not close enough to appear as a single star and while the conjunction may have led the Magi in the general direction of Bethlehem from Jerusalem, but did not stand over Bethlehem as stated in the Bible. 

Conjunction of Venus and Jupiter, 2015

A nova (“new star”) is star that suddenly flares up many times in magnitude. It is given this term because in most cases, it is a star that ordinarily is not visible to the naked eye. Similar to a nova is a supernova, a star which has exploded. Chinese and Korean records indicate either a nova or supernova occurred in the year 5 BC, which also fits the timeframe for the nativity. Unlike the planets, however, a nova or supernova would remain in a fixed position in the sky. 

Remnants of 1987 supernova (NASA)

A comet is best described as a dirty snowball orbiting the sun. Depending on location and trajectory, they can become visible to the naked eye as they approach the sun. The period of visibility and brightness vary from comet to comet, but as an object in orbit, it would certainly move about the sky. Chinese records indicate a comet appearing in the year 5 BC, which is within the accepted time of Jesus’s birth. The comet’s location in the sky would have it preceding the Magi first to Jerusalem, then to Bethlehem. It even appeared during spring, which is when it is believed he was born, even though we celebrate Christmas in December. That’s a different story for a different blog. 

Comet ISON (NASA)

Over 2000 years later, the great mystery of the Star of Bethlehem may finally have an answer thanks to forensic astronomy and the meticulous records of the Chinese. Was it really a comet, a completely rational cosmic occurrence, which led the Magi to Bethlehem? If so, did divine intervention place the comet where it needed to be at the right time? That question might never be answered.

This week's information comes from two sources. Speculation about conjunctions and comets comes from Colin J. Humphreys and the speculation about novae and supernovae comes from Mark Kidger.

Cloudy With A Chance Of Meteors

The Orionid meteor shower, happening through the end of October, reaches its peak October 20-22 (Friday-Sunday). Luckily, the peak nights for viewing are on a weekend; the best time for viewing the meteors, which appear to radiate from the constellation Orion, is around 2 AM. Expect to see about 20 meteors per hour.

The Orionids are named for the constellation they appear to radiate from. They are specks of dust and debris left by Halley’s Comet, which last made an appearance in 1986. Comets orbit the sun just like Earth, and leave behind a trail of junk as they orbit. They are basically giant, dirty snowballs and as they near the sun, they begin to melt somewhat, causing the debris trail. If a planet’s orbit crosses the debris field, whatever gets swept into the passing planet’s atmosphere will heat up and burn from friction. Odds are, those bright streaks you see in the night sky are no bigger than a grain of sand.

Meteor facts this week come from Space.com.