Database Entity Design for Enumeration Table
If there was any sort of choice to be made by your designers or users in the selection of these values I would go for the surrogate ID approach. What has been decided can be un-decided and the change will be easier with surrogates in place.

Since you are adamant the values are fixed by a Law Of Nature (or, at least, some external authority) I would be OK with using the single-column approach. In these circumstance the chances of change, and the wider impact, mean you'll likely have sufficient notice to effect the application update.