Expected behavior

An bad unit argument in u.format.fits.Fits.to_string() should raise a TypeError (or a ValueError if the type is correct).

Actual behavior

It raises an UnboundLocalError

Steps to Reproduce

import astropy.units as u

u.format.Fits.to_string(None)

gives

Traceback (most recent call last):
  File "<stdin>", line 1, in <modul

Is your feature request related to a problem? Please describe.
I'm studying geosat flares (link, link) and want to have a better idea of the cone of darkness that is created at a given distance.

Describe the solution you'd like
I want to select an object (satellite, moon, even planet) and see the

Description

As suggested from workshop, it would be nice to have the data units (e.g. cts, etc) printed on the .peek() histogram (pixel value plot) and maybe added to the colorbar of a map when plotted

or:

The units of a map are accessible via .unit. This is included in the peek colorbar, but not in the fancy html repr. It would be nice to include this too, maybe just as an additional

We could look into using the diskcache package to cache MAST search operations:

https://pypi.org/project/diskcache/

The package is a disk-based key-value store which makes it easy to specify an expiration time for each entry. This would allow us to e.g. cache search queries for 24 hours, which would significantly speed up searches across different Python processes, whilst largely avoiding

The python implementation of leapfrog does not make use of the fact that drifts can be combined when not storing output, causing it to be slower than necessary. Comparing to the C implementation, it also appears to not be as precise.