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skrap1r0n
2004-Mar-22, 06:59 PM
I grasp the general Idea of How this is accomplished. Point to an area of the sky, snap a picture (if you are capable), wait a preiod of time point to the same area and capture another image and compare the two images for movement.

Here are my questions:

1) what is the time frame needed between the images in order to see some movement?

2) Does the equitorial coordinate system change due to time of year? If I am looking at a section of the sky I have located using RA/DEC, will I be able to see that same area any time of the year as long as it is above the horizon using the same coordinates?

I have no pipe dreams about discovering an astroid, however it would be really neet to visually track a known one over time and capture it's progress.

Brady Yoon
2004-Mar-22, 07:11 PM
1) what is the time frame needed between the images in order to see some movement?
I cant give you a exact number, but it obviously depends on two major things-the distance from Earth and the relative angle of motion (a perpendicular moving object will show up more than a parallel moving object)

2) Does the equitorial coordinate system change due to time of year? If I am looking at a section of the sky I have located using RA/DEC, will I be able to see that same area any time of the year as long as it is above the horizon using the same coordinates?
It changes very slowly because of precession of the equinoxes, but it is neglible for your calculations.
This is probably wrong... :oops:

SarahMc
2004-Mar-22, 07:55 PM
1) what is the time frame needed between the images in order to see some movement?
I cant give you a exact number, but it obviously depends on two major things-the distance from Earth and the relative angle of motion (a perpendicular moving object will show up more than a parallel moving object)

True. The closer a comet is to perihelion, the faster it will "move" per observation. Comets close to perihelion can be observed to move over a number of minutes. Take a look at some images of comets, and you'll notice the background stars are streaked. In the short time the image was aquired (or numerous images stacked), the comet has moved in relation to the background stars.



2) Does the equitorial coordinate system change due to time of year? If I am looking at a section of the sky I have located using RA/DEC, will I be able to see that same area any time of the year as long as it is above the horizon using the same coordinates?
It changes very slowly because of precession of the equinoxes, but it is neglible for your calculations.
This is probably wrong... :oops:

No, you're correct. For all intents and purposes, the celestial grid remains the same from year to year. If you're refering to coordinates from 50 years ago, there'll be some obvious differences in some objects - some due to proper motion of the object, others due to the precession of the equinox, or both - but for the most part, it's irrelevant for observations. This is why the Epoch is given for more precise observations, and for future reference to historical records.

(edited for long fingernails)

skrap1r0n
2004-Mar-22, 08:04 PM
ok so If I knew there to be an asteroid at a certain location in the sky, I could point to those coordinates, take a picture, and then come back several days later, point to the same exact coordinates, regardless of time of evening/night, take another picture and then compare the images for movement?

SarahMc
2004-Mar-22, 08:18 PM
ok so If I knew there to be an asteroid at a certain location in the sky, I could point to those coordinates, take a picture, and then come back several days later, point to the same exact coordinates, regardless of time of evening/night, take another picture and then compare the images for movement?

Absolutely, although you'd need a pretty wide field of view. You're better off taking images over the course of a few hours for asteroids, to see movement. Over a few days, the asteroid would most likely move out of the field of view surrounding your pre-chosen coordinates. It depends quite a bit on the equipment you have to image with.

With two images over a three day period, the asteroid will just "jump" from it's position in one frame to another poistion - which you may not be able to see, and most likely will be out of the field of view.

If you image over 3 or four hours, you can see the object's movement easier. One long exposure (if you have the capability and a driven mount) will show the object as a streak against the backgroud stars.

Numerous shorter exposures can be "blinked", and will show the object as a stellar point of light, moving in a different manner than the stars do. This is the more common method for identifying asteroids, or for searching for new objects.

Ut
2004-Mar-22, 08:23 PM
Maybe.
It depends on the asteroid, and your field of view. In all likelyhood, though, the asteroid will not be there if you come back two days later and look in the same spot.
For my observation project in school this year, we were measuring the rotation period of some asteroids. They usually moved out of the field of view within 4 hours.

SarahMc
2004-Mar-22, 08:34 PM
After reading your other thread concerning the dob, I'd suggest that you try some planetary imaging with a webcam before you get too involved with astrophotography, and especially asteroids.

You need some very specific equipment to image asteroids, and I was under the assumption that you either had, or were planning to purchase ithat equipment.

Right off the bat, you'd need a driven scope. Most asteroids are well below the magnitude limit of non-CCD cameras, and you'd need at least a high sensitivity CCD on a non-driven scope to image asteroids.

Astrophotography, especially doing any kind of astrometry or photometry, requires a lot more than you have available to you right now. Maybe in your future astronomy endeavors, but not at this time, at least not without some great expense.

You'd have more enjoyment of imaging brighter objects, mostly planetary in nature with a webcam. Don't get me wrong, webcam imaging is a challenge all in itself - it's just more suited to your current equipment.

skrap1r0n
2004-Mar-22, 09:30 PM
You'd have more enjoyment of imaging brighter objects, mostly planetary in nature with a webcam. Don't get me wrong, webcam imaging is a challenge all in itself - it's just more suited to your current equipment.

Thanks thats where I was headed I suppose. At this point, I will most likely attempt the Web Cam form of astrophotography. I have been advised that Registax is a good program for cleaning up these images.

Also, the Time frame for asteroid movement is I guess where I was headed. Days hours or minutes. I realize there are a lot of variables involved, but it seems like hourly would be the best way to catch theses things.

Sorry about all the questions, I don't even have a scope yet, just trying to noodle out all the details so I won't make a regrettable decision once I do get a scope.