mirror in Shinto?

Only once, I was able to get a glimpse into the inner chamber of a shrine as a festival was in preparation and the priest was busy with the worship. I know, outsiders cannot enter into the inner chamber with the altar. But I could see a mirror from where I stood, i.e. in front of the donation box. I would like to know how the altar is composed in Shinto and what is the significance of the mirror? Would be grateful, if someone could answer!

Oh no! I just posted a reply and it is not showing up. Oh well.

The mirror is a very ancient symbol of Japan, along with the sword. The mirror is important because, in the creation myth of the Japanese islands, the sun goddess Amaterasu Omikami was lured out of a cave with the use of a mirror. I cannot really explain the story, but you can read about it here: http://en.wikipedia.org/wiki/Japanese_mythology

Shinto altars, whether at a shrine or at home (home altar is called 'Kamidana') or more or less the same, the main difference is, of course, the size. The plant offering is always leaves of the sakaki tree, considered sacred in shinto. The offerings are water, uncooked rice, salt, sake

At home, 'ofuda' are placed in the altar. Ofuda are three strips of white paper with writing on them, generally showing a connection to the sun goddess. Because it is Japan, there is a strict way to place ofuda in the home altar, and a strict way to place offerings in front of the shrine, be it at home or at shrine. People usually purchase new ofuda on or shortly after the new year, assuming they have a kamidana. This link, though in Japanese, shows the proper way to place the ofuda in the shrine, and below, shows several acceptable ways to arrange the offereings: http://www.tsukudo.jp/sahou-kamidana.html

Shrines, as well as home altars, should face the east (direction of the rising sun). If that is not an option, south is acceptable, but the 2 other directions are bad luck. Also, miniature mirrors can be purchased at religious supply stores, of the at the shops of some larger shrines and placed in front of a home altar.

There are many religious supply stores in Japan. In Tokyo, the neighborhood of Asakusa has many, and they are interesting to look through. They usually sell both Shinto and Buddhist home altars and supplies.

My grandmother taught me all about this, but today, many Japanese don't know how to properly arrange offerings, etc. Hope this answered your questions :-)

http://www.mikubi.or.jp/kamidana.htm#%8C%E4%90_%95%84%82%CC%...

This link also shows how to arrange the ofuda, and the proper ways of arranging the offereings

I had read in some texts the official view of the Shintoist as the following.
The Gods of Shinto are the unviewable holy spirits. The holy spirits descend to the sacred objects called Goshintai. Sometimes, Goshintai are mountains, big trees, rocks or sword. But in the most usual cases Goshintai are mirrors.

My opinion (archeological and historical)
Many many mirrors were found as artifacts from an excavation, at the remains of Yaoi era and Kofun era. From 3rd century our ancestor considered mirror as a sacred object.
The mythology of Japan has been written above.
And one of Imperial three Regalia is the mirror.
http://en.wikipedia.org/wiki/Imperial_Regalia_of_Japan

Thank you so very much!