Astronomy binoculars are often said to be the best first telescopes to slowly introduce you to sky gazing and astronomy. With wider field of view than telescopes they allow you to scan the whole sky at once and easily track the observing object. They are more portable, lighter, less bulky and do not require a tripod because lower magnifications bring less shaky images and easier handling. The main advantage of astronomy binoculars is that you are allowed to see with both of the eyes, giving you more natural viewing and easier tracking of the objects - two barrels collect more light. An important factor in astronomy binoculars is the size of the objective lens as they are mostly used in low light situations (at twilight or in pitch dark). The bigger the lens, more light is let through. Increase in light, high quality optics and coatings all contribute to brighter and more detailed image. Astro binoculars may be only water resistant which is enough of a feature to protect your binoculars before dew and moisture occurring at night. Waterproof and fog-proof features just add to the price.
Astronomy binoculars may not be a replacement to a telescope, they are simply an addition.