First astronomy since moving to Tonbridge

[john.clark]

I've measured the distance to Neptune!

I used 10 photos like this: http://www.finerandd.com/astronomy/Neptune%20&%20surrounds%202009%2007%2026.pdf.  Most were taken with a DSLR with a 500 mm catadioptric lens.  The image quality from this lens is pretty grim, especially the coma, and it is an [expletive, deleted] to focus, but it does give good star positions.  I can reproducibly measure the position of Neptune to within 2.5 arc seconds of the published position; and often get within an arc second.  You need about a dozen nearby stars to get a robust position for the orbiting object that does not depend on the stars you choose.

Neptune moves by barely more than a degree during each apparition, so it takes a bit of care to track its orbit.  When I worked outthe orbit of Mars, I was barely measuring to better than an arc minute.  You can't get away with that level of accuracy here.

I calculated the orbit using the method in my book http://www.springer.com/astronomy/book/978-0-387-89560-4, which assumes coplanar circular orbits for Neptune and the Earth.  (I have donated a copy to the OAS library.)  This method was deliberately designed to require no more than A-level maths. In fact it mostly consists of pre-GCSE geometry.  Anyone who can program Microsoft Excel could do it.

It will be interesting to see if the result improves as I get more pictures over the next few weeks - my distance is about 3% short.

The result is given at http://www.finerandd.com/astronomy/Neptune_circular_orbit_method.pdf.

[Ian]

Nice work John.

I had a think about it and reckon this is probably the better place for this topic as it's Astronomy related. We usually use Chat as a place to keep the bits of crud that turn up in the little strainer thingy in a kitchen sink...

[MarkS]

Interesting stuff!

Definitely looks like a topic for a members' evening presentation ...

[RobertM]

Neat work John, that's very interesting and I wouldn't mind having a go at that myself.

Ian, do you know who the librarian is ?

[Rick]

I have the library at my place. I will make sure the book is logged in ready for the next meeting.

[Ian]

Ian, do you know who the librarian is ?

He's orange, has very long arms and eats almost exclusively bananas.

Oh, hang on, you said librarian not Librarian.

That'll be Rick then...

[john.clark]

Neat work John, that's very interesting and I wouldn't mind having a go at that myself.

Now's actually a good time.  Jupiter, Uranus and Neptune are still around and becoming evening objects.  Mars will be with us shortly, an it won't be that long before Saturn is back in the morning sky.

You could do a lot worse than to start collecting photos and worry about how to analyse them later.  That's how I started. 

At first I used a webcam on a static tripod and let Registax do the tracking.  I got all my Mars data for the book that way.  Next I tried a webcam in afocal projection.  That worked a lot better.  I have several months' quite good data on Uranus which I still need to analyse ( ); but the webcam could not photograph Neptune.  Finally I moved to the DSLR and tried various techniques with it, all of which worked to some extent.  What I now do is piggyback it on a 6" Newt & use the Newt to guide.  I have had exposures up to six minutes come out well.  If you don't guide, 30 seconds is about the limit before the stars become trails. 

To guide on a bright planet, use the guide camera in afocal projection mode, not prime focus.  The planet is much smaller & the guiding software finds it easier to handle..

[RobertM]

John, I think it's best not mention a sensitive subject like Uranus in the forum.  You don't want the forum police getting involved.

Ian, not all librarians eat bananas http://www.youtube.com/watch?v=mZHoHaAYHq8

Thanks
Robert

[Ian]

Ian, not all librarians eat bananas http://www.youtube.com/watch?v=mZHoHaAYHq8

Oook?

[Rick]

OOOK!

[Ian]

that sounds like the Death of Librarians...

[john.clark]

I know.  What idiot named it that for corn's sake?  It wasn't Herschel.  He wanted to name it after his sponsor George III.  Everyoe else thought this was a daft idea...and look what they came up with!!

[Ian]

I think it was a deliberate ploy. I think someone said Astronomers have so sense of humour so we've now always got something to chuckle at next time someone asks, "what's the best way to observe Uranus?"

Of course, we're all serious astronomers here, oh yes.

We wouldn't dare put a mirror in our kit box, oh no...

[Carole]

Hmmm

Of course, we're all serious astronomers here

"What about the video at DSC and the 4 moons of ........"

C

[Ian]

what is the plural of Uranus, anyway?

It's at this point I would like to wholeheartedly apologise to John. IIRC post 1 was actually sober and properly scientific.

I think on reflection, I should have appreciated your prescience about putting this is chat, after all. It might go back there on the way to quarantine...