Celestial coordinates

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Celestial coordinates

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jan 14, 2010, 5:35 pm

Are there any helps, tools, instructions for an amateur sky watcher to measure ascension and declension?

jan 15, 2010, 6:07 pm

declension? In linguistics, declension is the occurrence of inflection in nouns, pronouns and adjectives, indicating such features as number (typically singular vs. plural), case (subject, object, and so on), gender, and possession.

or declination? In astronomy, declination (abbrev. dec or δ) is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle.

Are you talking about sighting a unknown object in the sky and calculating it declination and ascension. Or are you talking about taking finding a given object on map getting its known declination and ascension and then find that spot in the sky?

With my scope's goto system I have to give it the date and time and longitude and latitude. Then it goes to three targets that I "bracket". I can then enter a goto location. If I starhop by manually moving the scope it should give me hours minutes second for ascension and degrees for declination.

If you don't have "goto" you have to use "setting circle" I think the Norton's Star Atlas and Reference Handbook has the procedure for that method. Which I believe starts by locking in on a know star and matching "setting circles" on the telescope to that setting.

jan 15, 2010, 6:45 pm

What I'm trying to get at is how stellar coordinates are measured manually. My telescope is basic without any tracking tools. I have learned many of the stars and constellations and have a good feel for right ascension and declination, but I was interested in learning to measure positions manually - like maybe with an astrolabe (which I also do not have).

The two things that spurred this question are 1) trying to measure the movement of Mars away from Leo right now and 2) curiosity about how Hipparchus was able to discover precession by comparing the shift in the position of the stars from earlier observations.

I have not been able to find how the positions are measured with simpler tools.

A better locator (and better telescope) will be helpful to locate some of the less visible objects, but right now my interest is probably more basic.

Redigeret: jan 19, 2010, 11:28 am

I think maybe you want a theodolite more than a astrolabe. But hey it's not like you're navigating to the moon.

Do you have a good watch and telescope? If you want a crude measurement you can put Mars on the edge of your field of view and the mark the time. Then time how the rotation of the earth takes to move a known star into view. If you do this over several nights the time will get larger and larger as Mars moves away. Or you can swap this a known star that mars is moving toward.

How Hipparchus made it's determination of precession is beyond me. I am sure it has a lot to do with inertial guidance, gyroscopes and FM.

jan 15, 2010, 7:21 pm

Measuring with a watch may be the best instruction for my purposes. Can't get much simpler than that.

Mars should be up over the trees here pretty soon. Thanks.

jan 19, 2010, 11:15 am

Let me know how it works.

Redigeret: jan 19, 2010, 5:49 pm

I did not have the results I hoped for. I could not find a close and visible star to use for the measure - certainly one that came within the 60mm aperture of my telescope. I had thought to use some fixed landmark with a fixed viewing position to accomplish the same thing, but I have not followed through on that.

I am reading through De revolutionibus - slowly. It is interesting that he used right ascension and declination. I wonder how far back that coordinate system was used, and how it was measured.

Copernicus mentions a sextant. I found this http://digital.lib.lehigh.edu/planets/group_assign.pdf

The topic is very interesting to me.

Thanks so much for following up on this.

ETA http://www.juliantrubin.com/bigten/tycho_brahe.html

jan 19, 2010, 1:06 pm

Interesting to me as well -- thanks for keeping us posted richardbsmith! I love a scientific historical reenactment.

Redigeret: jan 19, 2010, 4:32 pm

This might be handy Mars Location Some star in Cancer might work.

jan 19, 2010, 4:40 pm

Very handy. Maybe closer to Cancer I can find a convenient star. Will not give up on the idea. Thanks.

jan 27, 2010, 7:14 pm

Well, just to report in. Since tonight is the first visibility since 1/19. I built a highly sensitive astronomical instrument - using a compass, a string and a nut, a ruler and a plastic straw and some tape. My wife is very impressed.

Anyway, from 1/19 to tonight I can report that Mars is 4 degrees closer to Pollux, according to my astronomical instrument. (That is when I remember to move my fat finger from obstructing the string.)

jan 27, 2010, 11:36 pm

My Grandfather used to have a theory that he could tell when we'd had enough dinner by the fatness of our little fingers. Have you remembered to factor in the fluctuating fullness of your finger to your complex calculation? ;)

jan 28, 2010, 6:04 am

I was not able to find a firm fat finger factor. Though it seemed to move Mars about 10 degrees, I think that error would vary with declination and finger placement more than fullness.