What' s the star that looks like a triangle called?

I think you're referring to the Summer Triangle but since we don't know where you live "from my deck" is not a very helpful reference point.

At the very least we would want the cardinal points (north, south, east, west, which I know you provided) and an angle from the horizon to the sky as well as the location where you live and the time you saw them. Without this complete list anything we say is just a guess. My guess is based on the assumption that you live in the Northern Hemisphere.

The Summer Triangle is not an official constallation, the phrase was coined by Sir Patrick Moore in his series The Sky at Night and it has been picked up by astronomers and used around the world as an "unofficial constallation".

It is formed by the three brightest stars in the constallations Cygnus the Swan, Lyra the Lyre, and Aquilla the Eagle. It's called the Summer triangle because in the Northern hemisphere it rises in Spring and sets in Autumn and is very easy to spot all the way through Summer.

You can find out more here:

http://en.wikipedia.org/wiki/Summer_Triangle

I don't understand what you're asking here. There are no stars that look like triangles. All stars are so far away that they look like points of light: they have no shape. If you see a star that looks like a triangle, it is probably a problem with your eyes, astigmatism, that can be cured with glasses. The only other thing you might mean is a _group_ of stars in the shape of a triangle. The trouble here is that _any_ three stars in the sky form a triangle. So, unless you can make your question clearer, you're not going to get an answer.

[Edit] I have READ your question very carefully, but I still don't know WHERE your deck is located or what time of night you're referring to. The stars appear different from different locations, and there are people on this forum from all over the world. We live on a planet that rotates every 24 hours, so the stars that are in the southwest change hour by hour. Yahoo thinks you're in the United States, which narrows it down somewhat, except that Yahoo also thinks that _I_ am in the United States, which I am not. Anyway, from MY deck (in southern Ontario Canada) just after it gets dark, there are a lot more than three stars in the southwest. The three brightest are Sirius on the left and Betelgeuse over Rigel on the right. Above Sirius is Procyon, and to the right of Betelgeuse and Rigel is the planet Jupiter, brighter than all these stars, and the red star Aldebaran. See the picture below. Does this help?

Hmmm, ..., it hard to say. It would help if we knew your location and the time you were viewing those 3 stars. However, I'm going to guess that you live in the Northern Hemisphere and are looking Southwest around 6:00AM. If that's the case then you are quite possibly looking at two bright stars in the constellation Libra and the planet Saturn. This combination would form an almost perfect "right" triangle setting in the southwest.

This is only a guess as there are many other triangular groupings of stars that occur in the night sky.

One thing you could try on your own is to download the free planetarium app Stellarium (www.stellarium.org) to your PC, enter your location into the program, and simulate the sky over your house. Then you could identify what you are seeing on your own.