Why is it so much easier to discover asteroids by astrophotography than by telescopic observations?

Answer 1

Cameras have shutters that can stay open a long time, capturing movement among the stars as streaks. By watching the same scene in real time, it's like watching the hour hand move on a clock. You know it's moving, but it's so slow, our mind/eye doesn't see it.

Answer 2

Asteroids look like stars through a telescope. They move very slowly. Too slowly to see while you're looking down the eyepiece. However, their movement is what gives them away as asteroids and not stars. If you simply look down the scope and draw what you see on several nights, you'll never be sure that what seems to have moved has actually done so or if you just didn't put it in exactly the same spot each time.

It is easier to discover them photographically because you can put two photos of the same piece of sky taken several nights apart right next to each other and see if anything has moved. There is even a piece of apparatus to help you do this called a blink comparator. You put two pictures in it side by side and look down an eyepiece. They eyepiece is actually directed at a mirror which is tilted to reflect one image. You then flip a switch and the mirror flips over to reflect the other image. If you do this repeatedly any object not in the same place in the two pictures will skip from one place to the other each time you flip the switch. This is how Pluto was discovered.

Of course now it's even easier because you can use computer software to turn a sequence of images into movies or overlay the images directly.

So photography is the method of choice because you just can't see that an asteroid is an asteroid by looking. You have to observe its movement over several nights.

Answer 3

Many asteroids are very faint--so much so that, even if you happen to have a telescope pointed right at one, you won't see it. Also, since even if you do see it, it will be just a pinpoint of light that looks jsut like all the stars in the image.

However, if you make a long time exposure photograph, the very faind image will gradually become intense enough on the film to see. Also, because an asteroid wil move slightly against the background of stars, it will appear as an elongated image or streak--so it's easy to tell apart from the background stars.

Answer 4

Relative time spent in observation.

Using long exposure the stars will appeared as white elongated dots, the planets that are closer will appear to move slightly more producing short white lines but an asteroid that is moving at relative greater speed will produce a long white line.

A good example of this can be found in the link below

Answer 5

(1) Cameras have longer exposure times than retinas.

(2) Photographs can easily be directly compared.

Answer 6

i would think that because one is in still form and the other is moving