Star of Bethlehem

A depiction of the Star of Bethlehem. Image credit: Garrett W. / CC BY

Right around Christmas time, a lot of people come up to astronomers and ask what the Star of Bethlehem could have been. This “star”, also called the Christmas Star, is said to have appeared in the sky in time to announce the birth of Jesus Christ to the Three Wise Men, and would have lead them to Bethlehem, to honour the newborn. Modern astronomers are now trying to figure out what astronomical event might have appeared in the skies all those years ago as the Star of Bethlehem. In order to do that, it is first necessary to try and pin down the actual birthdate of Jesus. Historical clues recovered throughout many different sources seem to indicate that he may have actually been born around the year 5 B.C. Furthermore, some believe the Star of Bethlehem did not appear right when he was born, but perhaps a year or even more later. This wide range of years have left us with quite a few theories as to the real identity of the Christmas Star:

1) A series of two or more planets in near alignment in the sky may have been seen as a single very bright star. Using known planetary orbits, we are finding it difficult to find such an alignment to have occurred at the right time, unfortunately.

2) Some Chinese astronomers recorded a new star born from a supernova that was highly visible for 70 days in the constellation of Capricorn around 5 B.C. However, the religious scripts state that the Christmas Star moved from East to South over the course of many months, which cannot be so easily conciliated with a supernova progenitor.

3) A comet might have been the culprit, but they were typically seen as bad omens. Furthermore, we cannot find any other mention of such a noteworthy object in the literature.

4) Jupiter, a planet that can indeed be very bright in the sky, may have seemed near immobile due to it being at the end of one of its retrograde loops.

The verdict is still out as to what the Star of Bethlehem truly was. Despite all our technological advances, it may be difficult to backtrack to a definitive answer so many years in the past.

Merry Christmas!

Lifetime of our Sun

An artist's depiction of the life stages of our Sun, from birth to death as a white dwarf within a planetary nebula. Image credit: ESO/S. Steinhöfel.

It all started with a giant cloud of gas, some 4.57 billion years ago. This cloud of helium and hydrogen collapsed under its own gravity and formed a protostar. After 100,00 years, it became a fully formed star and began its hydrogen burning phase, otherwise known as its main sequence — its adulthood of sorts. This lasts a total of 10 billion years. Currently, our Sun is halfway through its main sequence stage. Even now, however, the Sun is going through changes, but they are indiscernible over a human lifetime. Every billion years, our star gets 10% brighter, as it marches towards the end of its life. Because of this, the Earth’s surface will be too hot to sustain liquid water, and, in all likelihood life, in one billion years. To make matters worse, the Sun is expected to swell up to a few hundred times its current size in 5 billion years, when it becomes a red giant. At this point, it will have swallowed up Mercury, Venus, and possibly even Earth!

In one final gigantic tremor, our red giant Sun will expel its gaseous outer layers, forming an expanding planetary nebula, and leaving only a faint white dwarf at its centre. The layers of the planetary nebula will sweep through our Solar System and reach the interstellar medium, where they might one day join a gas cloud and lead to the formation of another star. As with the living creatures on Earth, we observe a beautifully cyclic nature in the lifespan of stars.

The Solar Cycle

A solar cycle: a montage of ten years' worth of Yohkoh SXT images, demonstrating the variation in solar activity during a sunspot cycle, from after August 30, 1991, to September 6, 2001. Credit: the Yohkoh mission of ISAS (Japan) and NASA (US).

The evolution of our Sun will happen over the course of billions of years. While this timeline is not accessible for us to observe in our lifetime, the Sun’s cycle is! Although less impressive than the changes it will go through over its lifetime, the Sun will see some significant changes over a cyclical period of 11 years.

We have been observing sunspots on the solar surface for millennia, but it wasn’t until the 19th century that scientists started noticing a certain regularity in their appearance and abundance. These sunspots are regions of the Sun’s surface where intense magnetic activity reduces temperature. Although still very hot (2750 to 4250°C), they appear darker in contrast to the surrounding regions that are about 5500°C. They crop up in greater number during a solar maximum, and are often accompanied by solar flares or prominences — ejections of huge clouds of particles and energy from the surface of the Sun.

While the Sun appears considerably more active in ultraviolet light during a maximum, the total energy output only increases by about 0.1%. These maxima are thus not expected to impact global climates, although they can slightly affect some regional weather patterns. The last maximum occurred in 2000, and with a cycle of about 11 years (but which can vary from 9 to 14 years), that would put the next maximum right about the end of 2012: truly great fodder for all 2012-end-of-the-world believers. Happily, you can rest assured that the next solar maximum is of no threat to us, and we have gone through a great number of solar cycles without much of a hitch. While it is true that solar flares and more violent solar activity can sometimes disrupt some of our radio communication systems, we are greatly protected from any actual danger by our Earth’s magnetic field. On the upside, we also see a greater abundance of the beautiful aurora borealis in the polar skies! Furthermore, NASA scientists believe that the upcoming solar maximum may be the weakest one since 1928. Once again, Earth seems to have averted total destruction!

2012 Apocalypse via Galactic Alignment

The X-ray view of the supermassive black hole at the centre of the Milky Way Galaxy. Image credit: NASA/CXC/MIT/F. Baganoff, R. Shcherbakov et al.

This is the Doomsday Scenario I’ve personally encountered the most, perhaps because it deals with things seemingly less outrageous than giant planets slamming into our us? As things go about their merry way in space, orbiting about one another, certain alignments are bound to happen. As with anything rare (OMG I JUST SAW A BLACK CAT SLAM INTO A MIRROR UNDER A LADDER WHILE OPENING AN UMBRELLA INDOORS WHAT ARE THE ODDS???), people like giving some significance to these events. Partial planetary alignments occur now and again, but do you know what’s even scarier than a planet? Why, a supermassive black hole(Sagittarius A*, to close friends) at the centre of the Milky Way, of course! Silly you.

Some have been saying that the Mayan calendar has been constructed around the alignment of Earth, the Sun and the Galaxy’s centre, which they say will happen on December 21st 2012, at which point everything will explode, or something. Truth is, it’s not actually going to happen on that date. Even better, were it to happen, Sagittarius A* is just so darn far away from us that it wouldn’t matter. Despite being over a million times more massive than our Sun, the fact that it’s 30,000 light years away means its gravitational effect would be insignificant compared to the pull we feel from our Moon. Even betterer, the actual alignment happened in 1998, so… Unless you count Britney Spears releasing her hit song …Baby One More Time as the apocalypse, I think we came out of that alignment relatively unscathed. Chances are, the same will happen this December (is Britney due for a new album?).

2012 Apocalypse via a Colliding Planet!

V838 Monocerotis, a variable star shrouded in a dusty halo. Image credit:  NASA and the Hubble Heritage Team (STScI/AURA).

Peppered over the year, we will be looking at different scenarios brought forward by a variety of people as how the year 2012 will bring about our demise. This month, we’ll be discussing the supposed collision of our own Earth and a planet named Nibiru, also known as Planet X. The Planet X hypothesis has been kicking around for a long time. As far back as the 19th century, scientists thought an unknown planet in the far reaches of our Solar System larger than Pluto was necessary to explain certain discrepancies in the orbits of Uranus and Neptune. These were later solved without the need for such a planet, and the issue has mostly been laid to rest in the scientific community.

Enter one Nancy Lieder in 1995. Convinced she has been elected by a race of aliens inhabiting the Zeta Reticuli star system to warn us of our impending doom, she has been hard at work spreading the good word over the internet. Initially, she stated that the planet Nibiru, supposedly 4 times the size of the Earth, would be sweeping through our Solar System on May 2003 before finally colliding with Earth. She states that even a near collision could be deadly, as interactions with Nibiru’s magnetic field would stop our own planet from rotating for an extended period of time, causing terrible, horrible things like displacement of the Earth’s crust. Obviously, May 2003 came and went and nothing of the sort happened. Logically, Lieder opted to argue that she had lied about this first date to “fool the establishment”… whatever that means. But if you’ve always dreamt of witnessing a planetary collision from a particularly close vantage point, never fear! “Experts” now say this mammoth event should happen in December 2012. Lucky us!

Obviously, there’s no real proof that any such planet with any such malevolent intentions is out there in our Solar System. An object of such a size would have been visible by now, yet there have been no visual confirmations of Nibiru or Planet X or Kerplowksiker. Of course, if NASA is part of “the establishment”, then it might all be a coverup. Furthermore, the orbit of this planet as described by Lieder has been found to be highly unstable by credible astronomers, and it would have been ejected from our Solar System within a million years of its creation. There are basically a bunch of reasons why we shouldn’t worry about this scenario coming to pass. If you’re curious, you can read up a little more on this topic here.

If you’re worried about our 2012 scenarios, and just can’t wait for me to talk about them, go through this neat NASA FAQ to ease your mind.

Until next month! Just because the world isn’t ending this year doesn’t mean we shouldn’t make the most of it!