astronomy facts

One of the originally planned tasks for the evening was to verify the alignment of the Orion Atlas mount's polar scope. Manuel dropping his C8 put the kibosh on that. I also really wanted to do it in daylight... While I checked the SCT for damage and collimated it, Manuel and I discussed a few science and astronomy topics.

Still, I was thinking about getting decent polar alignment while on this south-facing deck. A concept I wanted to share with him was magnetic declination. Knowing it, and having a compass, without being able to see Polaris, he'd still be able to get pretty close to the North Celestial Pole. I showed him the online calculator provided by Natural Resources Canada and how to use the information with his basic compass.

We briefly discussed the colour of stars... Manuel said that blue stars were young and orange were old. I wondered if that was strictly correct. I said it was my understanding that colour indicated temperature. He disagreed. I didn't think stars changed colour over their lifespans. I made a note to review stellar classification.

At one point, Manuel wondered if Mars was closer than Venus. I said I didn't think so. My gut feeling was that, while Mars was getting closer to us, for the upcoming March opposition, and at "perfect" oppositions (like the one in August 2003), it would get very close to the Earth, it would still always be a bit further than how proximal Venus would get.

We checked the amazing Wikipedia for the numbers. Mars at aphelion would be (approximately) 1.7 AU from the Sun; and at perihelion 1.4. Right. A very elliptical orbit. The semi-major axis was 1.5 AU. Venus on the other hand, in a more circular orbit, had a semi-major axis from the Sun of 0.7 AU. So, doing the quick math in my noggin showed that the closest we'd ever get to Mars would be 0.5 whereas to Venus could go as low as 0.3.

Now that he had an up-to-date Moon AVI file, we also discussed how to share it with members, for his upcoming DDO presentation. I suggested that he provide a very small version, with hundreds of frames vs. thousands. It would give people a taste, let them try stacking, but without bogging down their computer, particularly if older, and without requiring huge upload, download, and storage requirements. But Manuel insisted that they would need a full 4000 frame file.

§

The star colour topic kept bugging me... I found an interesting article in the astrophystics section of the Australian Telescope National Facility web site. I noted the remark near the beginning: "The colour of a star is primarily a function of its effective temperature." I thought so.