Sunday, December 13, 2015

Comets, Meteor Showers and Science Denial

So it's mid-December and the internet is busily hyping the Geminid meteor shower, supposedly the best of the year. Meteor showers, to me, are one of the most irresponsibly hyped celestial phenomena. And the damage is far from harmless.

Meteor Showers

Meteor showers happen when the earth crosses the orbit of fine debris, shed by a comet or asteroid. In some cases, we know the specific source. In other cases the parent object is long dead or had its orbit perturbed. The meteors appear to radiate from a single point just like snowflakes in your headlights do. It's a perspective effect - their paths relative to you are actually parallel. Meteor showers typically peak after midnight because that's when your location on earth is facing forward in its orbit. 

Yes, there are daytime meteor showers. How do we know? Because the ionized trails of the meteors affect radio signals and can be detected on radar.

The Geminids are expected to display about 120 meteors per hour, and by meteor shower standards, that's pretty intense. To get an idea what it's actually like, say "whee!" then count slowly for 30 seconds and say "whee!" again. And that's assuming you'll see every meteor. You won't. Many will be outside your field of vision, Expect more like one every two minutes. 

If you're a non-scientist, imagine someone promises you a great fireworks display, but you have to get up at 3 AM to see it. Then, every two minutes, someone tosses a sparkler in the air. And worse yet, he seems genuinely impressed. Will you trust that person next time he promises something?

No meteor shower shower should be described as strong unless it displays 1000 or more meteors an hour. What shower is that? Well, there isn't any. There are rare "meteor storms" that exceed that rate, the most famous being the Leonid shower in November. The Leonids were spectacular in 1833 and 1866, and produced a spectacular burst in 1966. Astronomers have had some success in predicting the orbits of dense swarms of particles and predicting outbursts. Unfortunately, the bursts tend to be short and geographically localized. But at least it can be worth getting out of bed to check.


Rivaling meteor showers for irresponsible hype are comets. Comets are generally discovered far from the sun and travel long eccentric orbits. So there's a long lead time before the comet passes close to the sun or earth. Once upon a time we wouldn't know about a major comet until it became pretty obvious, but now sky patrols pick them up when they're quite faint.

Sometimes a comet lives up to the hype. Comet Hale-Bopp in 1997 was detected far from the sun and was visible to the unaided eye for over a year. It set records for duration and distance of visibility. And it won't come back for several thousand years. It was brilliant in a dark sky and, for the first time in human history perhaps, billions of people were able to see a comet as a thing of beauty instead of a fearful portent of disaster.

And there are surprises. Comet Holmes had been plodding uneventfully through the inner Solar System every 6.9 years since its discovery in 1892. Then, in October, 2007, it had the greatest outburst ever seen in a comet, and brightened half a million times from a faint object visible only in large telescopes to something easily visible to the unaided eye. It actually attained a diameter greater than the Sun, though the total amount of mass was tiny. Payoffs like that are why amateur astronomers watch "dull' comets.

But for the average non-scientist, the experience is more like Comet Kohoutek in 1973. Kohoutek was believed to be a visitor from the remote Oort Cloud on its first visit to the inner Solar System. First time comets are a notorious crap shoot. They can release spectacular amounts of gas and dust and be dazzling. Or they can be so tightly frozen that they release little material. That's what happened with Kohoutek, and after the media hype, Kohoutek became a synonym for spectacular failures. Something similar happened to Comet ISON in 2013. ISON was discovered far from the sun and was following the orbit of numerous other comets that had close passages by the Sun. So a year out, the astronomical community was buzzing about the potential show. But ISON failed to brighten as hoped, and worse yet, it evaporated passing the Sun. Images taken after closest encounter showed a short-lived diffuse cloud that rapidly dissipated.

Even comets that put on spectacular displays can disappoint if their brightest appearance is so brief that bad weather can blot it out. Or a comet can appear briefly and unfavorably for one hemisphere and be spectacular in the other. Perversely, they seem to favor the Southern Hemisphere.

One comet I recall was Hyakutake in 1996, one of the closest comets to earth in centuries. Unfortunately, my observing site was a floodlit compound in Bosnia. A few weeks earlier, my team had been out after dark under a dazzling sky, but not when Hyakutake came by. Armed with only vague descriptions of the location in Stars and Stripes, I tried my best to view it from the shadows and saw nothing. But I bet that was the experience of most urban dwellers who tried, as well.

Based on my own experiences being disappointed by comets, I think a comet should be reported in the mass media only if it will be brighter than magnitude zero (a very bright star) in a dark sky and at least 30 degrees above the horizon. Report it only if the comet would be obvious to an urban resident with no knowledge of the constellations. And report it when and if it happens, not a year out like ISON or Kohoutek.

So What's the Harm?

If people can't trust science to tell them accurately what they can expect to see from their own back yards, why should they trust science when it tells them about climate change, GMO's, vaccination or evolution?