From 37233b05bd02b3730933b7d50c17780f55aeb550 Mon Sep 17 00:00:00 2001
From: "Albert Y. Shih" <ayshih@gmail.com>
Date: Fri, 8 Sep 2023 09:27:58 -0400
Subject: [PATCH] Use obstime from observer if obstime not otherwise provided

---
 changelog/7186.feature.rst             |  1 +
 sunpy/coordinates/frames.py            |  4 ++++
 sunpy/coordinates/tests/test_frames.py | 11 +++++++++++
 3 files changed, 16 insertions(+)
 create mode 100644 changelog/7186.feature.rst

diff --git a/changelog/7186.feature.rst b/changelog/7186.feature.rst
new file mode 100644
index 00000000000..dfef101eaf3
--- /dev/null
+++ b/changelog/7186.feature.rst
@@ -0,0 +1 @@
+When creating a coordinate or coordinate frame without specifying ``obstime``, the ``obstime`` value from the ``observer`` frame attribute will be used if present.
diff --git a/sunpy/coordinates/frames.py b/sunpy/coordinates/frames.py
index 9a3acecf0b8..4606188946f 100644
--- a/sunpy/coordinates/frames.py
+++ b/sunpy/coordinates/frames.py
@@ -133,6 +133,10 @@ def __init__(self, *args, **kwargs):
         if not kwargs.pop('wrap_longitude', True):
             self._wrap_angle = None
 
+        # If obstime is not provided but observer has an obstime, use that as the obstime
+        if 'obstime' not in kwargs and 'observer' in kwargs and getattr(kwargs['observer'], 'obstime', None) is not None:
+            kwargs['obstime'] = kwargs['observer'].obstime
+
         super().__init__(*args, **kwargs)
 
         # If obstime is specified, treat the default observer (None) as explicitly set
diff --git a/sunpy/coordinates/tests/test_frames.py b/sunpy/coordinates/tests/test_frames.py
index e65a96fa8b6..b8db7236356 100644
--- a/sunpy/coordinates/tests/test_frames.py
+++ b/sunpy/coordinates/tests/test_frames.py
@@ -231,6 +231,17 @@ def test_hpc_low_precision_float_warning():
         hpc.make_3d()
 
 
+def test_hpc_obstime_from_observer():
+    # Test that observer.obstime is used for obstime if obstime is not provided
+    observer = HeliographicStonyhurst(obstime='2023-09-08')
+    hpc = Helioprojective(observer=observer)
+    assert hpc.obstime == observer.obstime
+
+    # Test that obstime is None if observer does not have an obstime
+    hpc = Helioprojective(observer='earth')
+    assert hpc.obstime is None
+
+
 # ==============================================================================
 # ## Heliographic Tests
 # ==============================================================================