An emission nebula is a nebula formed of ionized gases that emit light of various colors. The most common source of ionization is high energy photons emitted from a nearby hot star. Among the several different types of emission nebulae are H II regions, in which star formation is taking place and young, massive stars are the source of the ionizing photons; and planetary nebulae, in which a dying star has thrown off its outer layers, with the exposed hot core then ionizing them.
Usually, a young star will ionize part of the same cloud from which it was born although only massive, hot stars can release sufficient energy to ionize a significant part of a cloud. In many emission nebulae, an entire cluster of young stars is doing the work.The nebula’s color depends on its chemical composition and degree of ionization. Due to the prevalence of hydrogen in interstellar gas, and its relatively low energy of ionization, many emission nebulae appear red due to the strong emissions of the Balmer series.
If a website gives a detailed guide for measurements, I feel more confident when ordering. Having a tracking number that works on common sites is very convenient. Shipping speed is not everything, but extremely slow delivery is very annoying. Recently I have been testing several online eyewear shops to compare frames and lenses.
If anyone is interested in real user experiences, I sometimes write short notes about the shops I test.
You can find one of the pages here:
click here
Now I am more careful with impulse buys and limited time offers. Having a tracking number that works on common sites is very convenient. Price is important to me, but quality and comfort are even more important in the long run. Some care only about style, others focus on comfort and durability.
Just sharing my personal feedback.
I prefer simple designs that do not depend only on heavy filters in the pictures. If the first order goes well, I slowly try more products from the same place. If anyone has long term experience with certain online shops, I am always curious to read it. This is why I like reading and posting on forums and community websites. Forums, blogs and communities create a kind of collective memory for shoppers. I think it is better to build a small collection of reliable products than to buy random cheap things.
If anyone is interested in real user experiences, I sometimes write short notes about the shops I test.
You can find one of the pages here:
check this link
A product that still looks good after a few months is more impressive than something only good on arrival. If the first order goes well, I slowly try more products from the same place. A simple pair of glasses or a basic jacket that always works is worth a lot. Loose hinges make the glasses slide down the nose again and again. Comfort around the heel and toes is more important than super fancy design.
Just sharing my personal feedback.