Repository: sunpy/sunpy

Issue:
Old EIT Maps are unable to have their date parsed correctly.
### Describe the bug

EIT fits files have the date-obs field in the form '01-Jan-96' which means they cannot be parsed by astropy.time.

They have an alternative date_obs which has the datetime in the correct format.

### To Reproduce

```
from sunpy.map import Map
import wget

wget('https://soho.nascom.nasa.gov/data/summary/eit/1996/12/seit_00171_fd_19961211_1900.fts')

Map('seit_00171_fd_19961211_1900.fts')
```

`ValueError: Input values did not match any of the formats where the format keyword is optional: {'datetime': TypeError('Input values for datetime class must be datetime objects'), 'ymdhms': ValueError('input must be dict or table-like'), 'iso': ValueError('Time 11-DEC-96 does not match iso format'), 'isot': ValueError('Time 11-DEC-96 does not match isot format'), 'yday': ValueError('Time 11-DEC-96 does not match yday format'), 'datetime64': TypeError('Input values for datetime64 class must be datetime64 objects'), 'fits': ValueError('Time 11-DEC-96 does not match fits format'), 'byear_str': ValueError('Time 11-DEC-96 does not match byear_str format'), 'jyear_str': ValueError('Time 11-DEC-96 does not match jyear_str format'), 'astropy_time': TypeError('Input values for astropy_time class must all be same astropy Time type.')}`

### Screenshots

_No response_

### System Details

_No response_

### Installation method

_No response_


Discussion:

Resolving patch:
diff --git a/sunpy/map/sources/soho.py b/sunpy/map/sources/soho.py
--- a/sunpy/map/sources/soho.py
+++ b/sunpy/map/sources/soho.py
@@ -42,6 +42,11 @@ def __init__(self, data, header, **kwargs):
         self.plot_settings['norm'] = ImageNormalize(
             stretch=source_stretch(self.meta, PowerStretch(0.5)), clip=False)
 
+    @property
+    def date(self):
+        # Old EIT data has date-obs in format of dd-JAN-yy so we use date_obs where available
+        return self._get_date('date_obs') or super().date
+
     @property
     def spatial_units(self):
         """


Test patch:
diff --git a/sunpy/data/test/seit_00171_fd_19961211_1900.header b/sunpy/data/test/seit_00171_fd_19961211_1900.header
new file mode 100644
--- /dev/null
+++ b/sunpy/data/test/seit_00171_fd_19961211_1900.header
@@ -0,0 +1,41 @@
+SIMPLE  =                    T / conforms to FITS standard                      
+BITPIX  =                  -64 / array data type                                
+NAXIS   =                    2 / number of array dimensions                     
+NAXIS1  =                  128                                                  
+NAXIS2  =                  128                                                  
+DATE    = '11/12/96'           / Date of file creation                          
+TIME-OBS= '19:00:14'                                                            
+DATE-OBS= '11-DEC-96'          / UTC at spacecraft                              
+ORIGIN  = 'Rocket Science'     / Rocket Science = NASA GSFC                     
+DATASRC = 'realtime telemetry'                                                  
+TELESCOP= 'SOHO    '                                                            
+INSTRUME= 'EIT     '                                                            
+OBJECT  = 'full FOV'                                                            
+BUNIT   = 'counts / pixel'                                                      
+WAVELNTH=                  171 / 171 = Fe IX/X, 195 = Fe XII,                   
+FILTER  = 'Clear   '                                                            
+DATE_OBS= '1996-12-11T19:00:14.254Z'                                            
+SCI_OBJ = '    1705'                                                            
+OBS_PROG= 'none    '                                                            
+CMP_NO  = 'TBD     '                                                            
+EXPTIME =                0.875 / seconds                                        
+EXPMODE = 'backside'                                                            
+FILENAME= 'efr19961211.190014'                                                  
+CFTEMP  =   -66.70999999999999 / CCD cold finger temperature (C)                
+CCDTEMP =                 7.47 / CCD temperature (DN/100)                       
+CTYPE1  = 'Solar-X '                                                            
+CTYPE2  = 'Solar-Y '                                                            
+CRPIX1  =           20.1796875 / Sun center x, EIT pixels                       
+CRPIX2  =          20.52421875 / Sun center y, EIT pixels                       
+CRVAL1  =                  0.0                                                  
+CRVAL2  =                  0.0                                                  
+CDELT1  =               67.072 / Pixel scale x                                  
+CDELT2  =               67.072 / Pixel scale y                                  
+SOLAR_R =               188.11 / Solar radius, EIT pixels                       
+SOLAR_B0=                -0.44 / Degrees                                        
+COMMENT SHUTTER CLOSE TIME =    2.024 s  LINE_SYNC = 'no'  CAMERA_ERR = 'yes'  I
+COMMENT MAGE_OF_SEQ =                    0  NUM_LEB_PROC =                    3 
+COMMENT  LEB_PROC = 26 (no image mask table)  LEB_PROC = 27 (no occ mask)  LEB_PCOMMENT ROC = 12 (Rice)  BLOCKS_HORZ =   16  BLOCKS_VERT =   16  P1_X =         
+COMMENT   1  P2_X =        1024  P1_Y =          20  P2_Y =        1043  N_MISSI
+COMMENT NG_BLOCKS =    1                                                        
+HISTORY Version 1.5, 1996 September 19
\ No newline at end of file
diff --git a/sunpy/map/sources/tests/test_eit_source.py b/sunpy/map/sources/tests/test_eit_source.py
--- a/sunpy/map/sources/tests/test_eit_source.py
+++ b/sunpy/map/sources/tests/test_eit_source.py
@@ -5,7 +5,7 @@
 
 import astropy.units as u
 
-from sunpy.data.test import get_dummy_map_from_header, get_test_data_filenames
+from sunpy.data.test import get_dummy_map_from_header, get_test_data_filenames, get_test_filepath
 from sunpy.map.sources.soho import EITMap
 
 header_list = [f for f in get_test_data_filenames() if 'efz' in f.name and '.header' in f.name]
@@ -54,3 +54,8 @@ def test_norm_clip(eit_map):
 def test_wcs(eit_map):
     # Smoke test that WCS is valid and can transform from pixels to world coordinates
     eit_map.pixel_to_world(0*u.pix, 0*u.pix)
+
+
+def test_old_eit_date():
+    eit_map = get_dummy_map_from_header(get_test_filepath("seit_00171_fd_19961211_1900.header"))
+    assert eit_map.date.value == '1996-12-11T19:00:14.254'