Friday, July 25, 2008

Sometimes we miss the obvious

A couple of days ago, I wrote a long spiel about the nova nobody saw, despite the fact that it should have been visible to the naked eye. Reasons I suggested for why people may have missed it included that the constellation is near the Milky Way, so rich in stars (true), that the southern hemisphere has fewer amateur astronomers (also true), and that the sky is big and we may be missing a lot of novae (yet again, true).

But I may have missed the most obvious reason: the time of year. Robotic telescopes pinpointed the date of the explosion as June 5. What I didn't recognize at the time is that the constellation Puppis is near Canis Major (the big dog), which is a winter constellation. (This hit me when I read the Wikipedia article on Puppis).

On June 5, at twilight in the southern hemisphere (specifically, I refer to -29 latitude, where the Las Campanas Observatory is located), the nova was 40 degrees above the horizon, and setting fast. Within two hours, it would have been lost in the murky skies.

Now, in the southern hemisphere, it was winter. Think about your normal winter schedule. It gets dark early; often you aren't home from work yet at sunset, and it has been dark a couple of hours by the time you've gotten home, had dinner, and have time to relax. I suspect that the same is true of all but the most dedicated amateur astronomers. By the time they got outside and set up for viewing, the nova would have set. Also, remember the nights are long (and colder) in winter, and in the later half of the night, the riches of the center of the Milky Way would have been high in the sky for prime viewing. And the center of the Milky Way is more likely to have novae than the region where Puppis is found.

So, I'd be willing to bet that, even among the best southern hemisphere amateur astronomers, not that many were "on duty" before the nova set. So, it is even less surprising that the nova was only seen by a robotic telescope, which would have no family duties to worry about.

From the northern hemisphere, the nova (which would just barely be visible in best viewing) disappeared below the horizon hours before sunset.

So, in short, everyone had a good excuse to miss the nova; I'm not so sure I had as good of an excuse for missing this obvious explanation. And I suspect misses due to sunlight are much more common than anyone would care to admit.

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