Icelandic feminine singular indefinite dative -u

[Skomakar'n]

I've been studying Icelandic on my own for about three years, and can speak it at a conversational level.
One thing that I still really haven't gotten the hang of, though, is why feminine datives in the indefinite singular sometimes take -u, when all the tables I've seen always list this form as the same as the nominative and the accusative (except for a couple of words such as hönd, of which this form is hendi).

The word I've mostly seen the -u with, is jörð, which tends to become jörðu in this form, but I know this from experience speaking and listening to Icelandic, rather than finding it in grammars, because tables always list this as jörð, in my experience.

This is the first sentence of the Icelandic Wikipedia article about solar eclipse:

"Sólmyrkvi (sem til forna var nefnt myrkur hið mikla) er það kallað þegar tunglið fer fyrir sólu frá jörðu."

As you can see, both sól and jörð get the -u here. So I'm very confused, as the tables I've seen show just sól and jörð.
I know out of experience that jörð is supposed to be jörðu, but I've not noticed it for sól before.

So do all fairly regular feminines take the -u in this form, or is it reserved for a few words? That would explain the misleading tables a bit better.

Also, would the definite form be jörðunni, or is it still jörðinni?

[Aszev]

http://bin.arnastofnun.is/leit.php?id=475966

Does that help?

I looked up a few words from different stems and it seems pretty random to me what words get this -u, but it doesn't seem to be more than a handful anyway.

[Magb]

Another noun that takes -u sometimes is nótt. Also, there's the large class of feminine nouns with the suffix -ing, for which -u is obligatory, though that could be an unrelated thing I suppose. In all these cases the -u is used for the accusative as well as the dative, by the way.

[Skomakar'n]

Another noun that takes -u sometimes is nótt. Also, there's the large class of feminine nouns with the suffix -ing, for which -u is obligatory, though that could be an unrelated thing I suppose. In all these cases the -u is used for the accusative as well as the dative, by the way.

I do know stemning does it, so that makes sense. Thanks.

http://bin.arnastofnun.is/leit.php?id=475966

Does that help?

I looked up a few words from different stems and it seems pretty random to me what words get this -u, but it doesn't seem to be more than a handful anyway.

A little. At least now I have a new, nice source. Thanks.

Why is this so rarely shown in tables, do you think..?

[Nannalu]

PFFFFFFFFFFFFFFFFFFT

Why do Icelandic when you can dooooo...........*drumroll*......... Faroese!

[Skomakar'n]

PFFFFFFFFFFFFFFFFFFT

Why do Icelandic when you can dooooo...........*drumroll*......... Faroese!

Eg dugi eit sindur av føroyskum! Eg dugi at tala íslendskt væl nú, so eg havi eisini byrjað at læra føroyskt.
Eg veit ikki um allt hetta er rætt, men tað er tað kanska. Eg elski ikki bara íslendskt!

[johanpeturdam]

Eg dugi eitt sindur av føroyskum! Nú dugi eg væl íslendskt, so eg eri eisini byrjað at læra føroyskt.
Eg veit ikki, um alt hetta er rætt, men tað er tað kanska. Eg elski ikki bara íslendskt!

Hygg hatta raska, Skomakar'n, hatta kláraði tú bara heilt væl.

[vec]

You use jörðu, nóttu and sólu in certain fixed phrases, að nóttu til, bregða hendi fyrir sólu, hann sté upp frá jörðu (sté is an old past form of steig), á jörðu niðri, eins og dögg fyrir sólu and a couple of others I can't think of. They're also used in poetry. Normally, though, you say jörð, nótt and sól etc.

While the elusive feminine dative -u is dependent on style and context, the masculine dative -i are truly optional, though, in all the words with a double form.