I understand that there are a number of people who were unable to see the comet …

Posted by: Astronomy by the Bay
I understand that there are a number of people who were unable to see the comet last night, based on all the comments. Many were disappointed. I was as well.
It may be worth explaining what might have been the cause, and to explain it initially using the term magnitude. Astronomers use this term to describe the “brightness” of an object. There’s an explanation for the numbering, but basically, the lower the number, the brighter the object.
Magnitudes are also exponential. For instance, an object that is magnitude 1 is actually 2.5 times as bright as an object that is magnitude 2…. and 6.25 times as bright as an object with a magnitude of 3. (2.5×2.5)
We all remember Comet Neowise when it offered a view in our night sky back in 2020. That comet reached a magnitude of 1.
Comet C/2022 E3 (ZTF) has so far reached an estimated magnitude of approximately 5. So, if we compare the two comets using the magnitude scale, we can see that this comet is about 39 times dimmer than Neowise at its peak (2.5×2.5x.25×2.5 = 39).
Another point is what we can see, our limiting magnitude, on any night. On a clear night, we can usually see about 4,000 stars from a dark sky site. That means that we can see stars down to about magnitude 6, so a lesser number would mean a brighter object and more chance to see it. That also means that your eyes must be dark adapted first.. allowing a period of time away from any light source for your pupils to dilate. This can be several minutes up to an hour… so if your observing site has lights of any type that pollute your view, you will not see objects as dim as mag 6. I was set up in a school parking lot last night, to avoid setting up on ice covered snow…. bad idea, because parking lot lights made it very difficult to spot the object naked eye… my eyes couldn’t get dark adapted.
Let’s keep going. Hard to believe, but clear skies don’t always mean great viewing. Something else is important… transparency. That is the moisture content in the air. Low transparency results in water droplets that scatter those photons of light, making it more difficult to see dim objects. Last night’s transparency was not great, as evidenced by my telescope dewing up fairly quickly.
Another reason is the diffused light from a comet. Comets are not pinpoints of like, like stars. Their light is scattered over a large area and is the result of the solar wind acting upon its substances.. so the light from a comet is more diffuse than say, the light from a planet like Jupiter… so dimmer light spread out over a large area.
Finally, it’s our eyes that can be the problem. Everything we see emits photons of light. When we look up at the night sky, those photons of light we see may have travelled through space for millions of years just to release their energy on our retina in one instant. Unfortunately, our eyes can’t store photons, like a camera sensor. With a sensor, capturing a long exposure allows those photons to build up on the sensor, creating a much more pleasing image. That part may be disappointing, until you realize that those photons you see with your eye would be wasted if you hadn’t been looking back at the same time… and when we see the light emitted from that object, we are seeing that object as it was in the past. That helps me understand why the view of a distant object in my eyepiece will never appear as nice as an image.
Add to all of this a bright Moon last night which added a certain amount of its own light pollution.
And then there’s the inevitable media hype. Comets. meteor showers, planet alignments make for great positive stories, so sometimes our expectations can be unrealistic as a result. I still love discussing events. Comets, meteor showers, etc. can be a pleasant surprise, and I take comfort knowing it may have more you take the time to look up, and wonder. There’s always more to a night sky to enjoy than just one object.
I hope these reasons help explain why our views are not always as pleasing as we expect. Will the comet get brighter? Comets are very unpredictable… we just don’t know. But we’ll still be watching, and I’ll continue to post updates about it.
See the chart below for a better explanation on magnitudes, and the limits of our eyes.
I’ve been in this hobby a long time.. and there are many frustrating moments… but you learn to develop patience, and staring back at the Universe and its many treasures has never been disappointing.
There’s always something waiting to show us its beauty.
Wishing all of you clear skies 🙂

Original Post