I was wondering if there was an easy way to tell whether a website is an authority site in Google. If you can get a backlink from an authority site that's in your niche, what does that do for your SEO?
From what i know an authority site is a site that is very well positioned for some important keywords. The links that are comming from this kind of sites are the most valuable inbound links (of course if they share the same niche)
A good way to test out authority is to come up with 5 keywords for your niche market, and see the to 10 competitors in google (page 1). If the same websites appear over and over, then they are authority. Also, web 2.0 sites such as digg,scribd,quizilla,blogger,wordpress,youtube,etc. are high authority, since they appear on the first page. If you get authority backlinks you can see your rank position soar to the top.
What are the requirements for being an authority site? Is it traffic and the number of pages your website has? Or does the website have to be consider "very well-known"? If that's the case, then I would guess that Google would probably have to manually set what websites are considered authority websites.
I think I figured out how to tell whether a website is authority or not. Simply search for a keyword and see if any websites come before the main search results that aren't sponsored. When you search for the word "videos", you can see all the authority websites appear above See results for: music videos. But when you search for the word "dogs", nothing appears above the main search results that isn't sponsored.
apart from top 3 ranks in numerous niche keywords, a good pagerank, link: comes back with related high ranking sites etc...
I don't think there's a specific definition for an "authority" website but this phenomenon is probably related to the pagerank of the domain in question. Google ranks pagerank into four categories in the webmaster tools: Not ranked - PR 0 Low - PR1 - PR4 Medium - PR5 - PR7 High - PR8 - PR10 Obviously, if you get some well positioned links on a Medium or High PR website you can get your own domain up there too. The more Google relies on brands it seems like the more frontpage PR matters for ranking of all sorts of keywords. Kind of like how Wikipedia and Youtube can rank for just about any keyword/phrase you can imagine.
That's because of the way the top sponsored slot is calculated - nothing to do with 'authority sites', which, as korr pointed out, isn't a fixed specific definition. To get the top slot above the search results in adwords the ad has to pass a high 'quality score' threshold, and you are less likely to get that for a vague word like 'dogs'
PR can be a good indicator - you wont see many trashy sites of PR7+ also look for .edu, in USA or .gov and .ac.uk domains in the UK
I don't know if PR has anything to do with it. That would mean that ANY website that "cheats" by buying high PR backlinks could be an authority website.
I had some sites that while searching for major keywords they appear as #1 and with 4-6 links bellow. Isn't this authority? They give one site the authority for that particular keyword(s)?
Nope. Those are called "sitelinks" and are not associated with "authority" anywhere in Google literature.