Objectives: To understand signal To understand noise Goal: To understand whether or not you will be able to photograph an object Objectives: To understand signal To understand noise

Signal To image an object you need light from that object The amount of light you collect that comes from the object is called signal

How to increase signal 1) use a bigger telescope. The collecting area of the telescope determines how much light you collect in a given time. PLEASE NOTE Area depends on radius squared

If I triple the diameter of a lens If I triple it how much more light do I collect? 1) 3 X more 2) 5 X more 3) 9 X more 4) 27 X more

The other way The other way to collect more light is to have a longer exposure time. The longer the exposure the more signal you get

Noise Signal is not enough, your signal needs to be 5 – 10 time higher than the “noise” There are many sources of noise

Statistical noise Take the square root of the number of photons you collect in a pixel of the camera. This is statistical noise. The more signal you get the bigger your statistical noise

Instrument noise Even if you took a blank picture you would still have some “counts” This is current that naturally occurs in your camera Most modern cameras take this into account in the final image

Universe Noise No matter what part of the sky you take a picture of there will be other objects bright and faint that will also add their own noise. Even dust in our solar system emits some light of its own (zodiacal light)

Moon scatter If the moon is up light from the moon will scatter off of the atmosphere. While bright objects are largely unaffected objects that are dim (deep sky objects) need to be observed when the moon is not up.

Light Pollution (from NASA)

Naked Eye 8th Magnitude in country 5-6th Magnitude in City Difference of about 10X in brightness (each magnitude is a factor of 2.5)

Small Telescopes How deep you can see will depend on: Where you are If the moon is up What part of the sky you are looking at The exposure time

Limits for naked eye 6-8” telescope depending on conditions can reach magnitude 13-15 (good enough to barely see Pluto) The 4” will not see as well, but should get close to 12th magnitude in the county.

Astophotography Will do better, but there are limits Longer exposure gives more signal BUT 1) more noise 2) if you don’t have tracking the stars will streak, and the further they streak the more the light is spread over many pixels so your signal no longer goes up but the noise still does

Expectations With exposure times of 10 seconds you should be able to get to about 15th magnitude on a good clear, moonless night, in the country In the city…. A lot less.

It is that time… You need to decide your project. In a moment we are going to follow me to the area where the telescopes and cameras are to hand out. You need to write on the back of your attendance worksheet your project idea.

Conclusion: We have examined signal We have learned about noise We have decided our projects and now if you will follow me we will pick up the equipment we need.