Why is my nighttime sky image so poor (few stars and a yellow glow)?

Question

I am new to astrophotography and I take most of my pictures at around 11pm, which is reasonably dark. The only lights which are on near me are street lights and they are behind trees.

I am struggling to take pictures though, and my final pictures seem to be full of noise, maybe 40 stars maximum. On top of that, there seems to be streaks of yellow and other colours going across the image if you look closely.

Another problem is that the bottom of my pictures seems to glow, almost as if there was a candle sitting on the floor radiating light into the picture. I don't know why my camera comes out with such bad pictures and can't pick up many stars.

My camera is a Canon Powershot G1X. I take my pictures at 2 seconds shutter speed (longer than 10 seconds, the picture becomes white), and I use ISO 12800 (I use this so my camera actually picks up stars. At 1600, it picks up fewer stars than my eyes.) and f/2.8.

Answer 1

lower your iso 1600-3200 tripod, increase shutter speed try somewhere between 15-20seconds work on the rule of 500 to avoid star trails. alternatively if can be faffed go research stacking... which can reduce noise effectively at higher iso than normal.

Answer 2

The yellow glow is light pollution. It doesn't take much at all to drown out most of the dimmer stars in the sky.

The penalty of using most compact cameras with a comparatively small sensor is that they don't do well in low light. The smaller the photosites (pixels) on a sensor are, the lower the difference between signal and noise will be, At some point the signal is just as strong as the noise and there are no distinguishable differences between the two. But the Canon G1 X has 4352x3264 pixels packed into a 18.7x14 mm sensor that is larger than the typical compact. This gives it a pixel pitch of 4.3 microns, which is comparable to a lot of slightly larger APS-C sensors in the 18 MP range. The 1.85X crop factor places it between 1.5-1.6 APS-C cameras and 2X micro four-thirds cameras.

Using sufficiently good astrophotography techniques and practices, you should be able to get better results than what you are seeing, but you're going to need some darker skies than your current location to do it.

Your first move after finding some darker sky should probably be to try and reduce the ISO to around 3200 or so and expose longer. This should help some with the noise problem. A way to further reduce noise is to use image stacking and dark frame subtraction. They're both well covered in other questions here.

There are plenty of existing questions here at Photography.SE with answers that should help you improve your astrophotography.

Some of the most applicable to your situation might be:

Longer exposure & lower ISO or shorter exposure & higher ISO - what gives better results when photographing stars?
Why do I have blurry star trails?
How to have colors in Milky-way?
How to take the night skies and meteor showers?
Astrophotography exposure setting for noise reduction
What caused my astrophotography images to come out hazy?
How do I get a shot of both the foreground and stars with astrophotography?
How to enhance a cameraphone photo so you can see stars?
How do star trackers work to take a photo for 5 minutes without blur, and are they worth it?
Black sky for night long exposure
What is the "Rule of 600" in astrophotography?
Can I get longer than 15 second exposure with my canon SX 50?
How to set white balance in a photo of stars?
Why should I use the widest aperture for star photography?
How do I focus in low light for long exposures?
Star photography: what aperture

Answer 3

The imaging chip works by converting photon hits to an electrical charge. These photosites are arranged in a grid pattern. Each contains a photodiode that that does this deed. Because the generated electrical charge is so weak, each photosite contains an amplifier. With so many photosites each will responds slightly different as to photon hits vs. amount of charge. Now add to this mix, each individual amplifier will toss in a slightly different level of boost. Normally this stuff is of no significance however, the night sky is a mundane expanse. What you are seeing is called noise. This is akin to static in an audio system. Turn up the volume and you get more volume but you also get more static. Your remedy is to turn down the ISO, that will reduce the amount of amplification thus you benefit by noise reduction. What you are seeing is “fixed pattern noise”. Shoot some samples with the lens cover on. This will clue you in as to what ISO setting to use.