diff --git a/pyuvdata/uvdata/uvfits.py b/pyuvdata/uvdata/uvfits.py
index b6fefff558..ea20ef9f88 100644
--- a/pyuvdata/uvdata/uvfits.py
+++ b/pyuvdata/uvdata/uvfits.py
@@ -11,6 +11,7 @@
 from astropy import constants as const
 from astropy.io import fits
 from astropy.time import Time
+from astropy.coordinates import EarthLocation
 from docstring_parser import DocstringStyle
 
 from .. import utils as uvutils
@@ -59,9 +60,11 @@ def _get_parameter_data(
             # angles in uvfits files are stored in degrees, so convert to radians
             self.lst_array = np.deg2rad(vis_hdu.data.par("lst"))
             if run_check_acceptability:
-                (latitude, longitude, altitude) = (
-                    self.telescope_location_lat_lon_alt_degrees
-                )
+                (
+                    latitude,
+                    longitude,
+                    altitude,
+                ) = self.telescope_location_lat_lon_alt_degrees
             uvutils.check_lsts_against_times(
                 jd_array=self.time_array,
                 lst_array=self.lst_array,
@@ -1158,8 +1161,18 @@ def write_uvfits(
             hdu.header["PSCAL" + str(i + 1) + "  "] = pscal_dict[key]
             hdu.header["PZERO" + str(i + 1) + "  "] = pzero_dict[key]
 
-        # ISO string of first time in self.time_array
-        hdu.header["DATE-OBS"] = Time(self.time_array[0], scale="utc", format="jd").isot
+        # Create an  astropy.time.Time object from first timestamp.
+        # This is used to generate DATE-OBS and RDATE keywords
+        eloc = EarthLocation(
+            self.telescope_location[0],
+            self.telescope_location[1],
+            self.telescope_location[2],
+            unit="m",
+        )
+        obs_date0 = Time(self.time_array[0], format="jd", scale="utc", location=eloc)
+
+        # Per AIPS memo 117, DATE-OBS is the YYYY-MM-DD string
+        hdu.header["DATE-OBS"] = obs_date0.strftime("%Y-%m-%d")
 
         hdu.header["CTYPE2  "] = "COMPLEX "
         hdu.header["CRVAL2  "] = 1.0
@@ -1338,26 +1351,21 @@ def write_uvfits(
         else:
             ant_hdu.header["FREQ"] = self.freq_array[0, 0]
 
+        # RDATE: Reference date when obs started, YYYY-MM-DD
         if (self.rdate is None) or (self.rdate == ""):
-            rdate_obj = Time(np.floor(self.time_array[0]), format="jd", scale="utc")
-        else:
-            try:
-                rdate_obj = Time(self.rdate, scale="utc")
-            except ValueError:
-                rdate_obj = Time(np.floor(self.time_array[0]), format="jd", scale="utc")
-
-        if self.rdate is None:
-            ant_hdu.header["RDATE"] = rdate_obj.strftime("%Y-%m-%d")
+            ant_hdu.header["RDATE"] = obs_date0.strftime("%Y-%m-%d")
         else:
             ant_hdu.header["RDATE"] = self.rdate
 
+        # GSTIA0: Greenwich sidereal time in degrees at zero hours on RDATE
         if self.gst0 is None:
-            ant_hdu.header["GSTIA0"] = rdate_obj.sidereal_time("apparent", "tio").deg
+            ant_hdu.header["GSTIA0"] = obs_date0.sidereal_time("apparent", "tio").deg
         else:
             ant_hdu.header["GSTIA0"] = self.gst0
 
+        # UT1UTC: the difference between UT1 and UTC in seconds on RDATE
         if self.dut1 is None:
-            ant_hdu.header["UT1UTC"] = float(rdate_obj.delta_ut1_utc)
+            ant_hdu.header["UT1UTC"] = float(obs_date0.delta_ut1_utc)
         else:
             ant_hdu.header["UT1UTC"] = self.dut1