sunpy · Cadair · Apr 9, 2026 · Apr 15, 2026 · Apr 15, 2026 · Apr 16, 2026
diff --git a/posts/2026/art2_eclipse_ship.jpg b/posts/2026/art2_eclipse_ship.jpg
diff --git a/posts/2026/artemis2-corot-traj.png b/posts/2026/artemis2-corot-traj.png
diff --git a/posts/2026/artemis2-distortion-fit.png b/posts/2026/artemis2-distortion-fit.png
diff --git a/posts/2026/artemis2-hough.png b/posts/2026/artemis2-hough.png
diff --git a/posts/2026/artemis2-initial-fit.png b/posts/2026/artemis2-initial-fit.png
diff --git a/posts/2026/artemis2-roll-fit.png b/posts/2026/artemis2-roll-fit.png
diff --git a/posts/2026/artemis_2_eclipse.md b/posts/2026/artemis_2_eclipse.md
@@ -0,0 +1,133 @@
+---
+blogpost: true
+date: Apr 9 2026
+author: Stuart Mumford, Shane Maloney, Albert Y. Shih
+category: Tutorial
+tags: eclipse
+---
+
+# Artemis II Solar Eclipse
+
+The Artemis II mission launched on the 1st April 2026, this launch date (or the window on the 2nd) allowed the crew to observe a solar eclipse on the 6th April after transiting the far side of the moon.
+
+```{figure} ./art2_eclipse_ship.jpg
+  :width: 66%
+  :alt: Artemis 2 Solar Eclipse with Capsule
+
+Image credit NASA
+```
+
+We on the SunPy blog {ref}`rarely miss the opportunity <2024-04-03-eclipse>` to talk [about a solar eclipse](https://github.com/sunpy/solar-eclipse/).
+So when we saw the stunning photos taken by the astronauts on Artemis II, we loaded them with SunPy.
+I do highly recommend watching the recording of the eclipse [on YouTube](https://youtu.be/dS9qqzSF3mI?si=NFfli3b7f0tYoVDP&t=1683).
+
+## Fitting Coordinate Information
+
+To be able to compare this image with other observations of the Sun, we need to identify where the camera was pointed and how it was rotated.
+To do this we perform the following steps, all the code for this example is in **the sunpy example gallery**.
+
+1. Extract the time information from the metadata on the camera.
+1. Use the time information to know the exact position of Artemis 2.
+1. Fit the edge of the moon to identify the location of the center of the moon, and the size of the moon in the image.
-1. Fit the edge of the moon to identify the location of the center of the moon, and the size of the moon in the image.
+1. Fit the edge of the moon to identify the location of the center of the Moon, and the size of the Moon in the image.
-1. Fit the edge of the moon to identify the location of the center of the moon, and the size of the moon in the image.
+1. Fit the edge of the moon to identify the location of the center of the Moon, and the size of the Moon in the image.
+1. Use the three planets visible in the lower right of the image to identify the rotation angle.
+1. Use the planets to fit the distortion of the lens.
+
+### Finding the position of Artemis 2
+
+The first step is to know the time the image is taken, we can extract this from the [Exif metadata](https://en.wikipedia.org/wiki/Exif).
+Once we have this we query [JPL Horizons](https://ssd.jpl.nasa.gov/horizons/) for the position of Artemis 2.
+
+```python
+from sunpy.coordinates import get_horizons_coord
+
+artemis2_naif_id = "-1024"
+artemis2_coord = get_horizons_coord(artemis2_naif_id , "2026-04-07 01:06:19")
+```
+
+We can also use the positions returned by JPL Horizons and the coordinates packages in sunpy and astropy to visualize what part of the Artemis 2 trajectory was in eclipse.
+To see the details of how this was done see [this example in the SunPy gallery](https://sunpy--8574.org.readthedocs.build/en/8574/generated/gallery/showcase/artemis-ii-trajectory.html).
-To see the details of how this was done see [this example in the SunPy gallery](https://sunpy--8574.org.readthedocs.build/en/8574/generated/gallery/showcase/artemis-ii-trajectory.html).
+To see the details of how this was done see [this example in the SunPy gallery](https://docs.sunpy.org/en/latest/generated/gallery/showcase/artemis-ii-trajectory.html).
-To see the details of how this was done see [this example in the SunPy gallery](https://sunpy--8574.org.readthedocs.build/en/8574/generated/gallery/showcase/artemis-ii-trajectory.html).
+To see the details of how this was done see [this example in the SunPy gallery](https://docs.sunpy.org/en/latest/generated/gallery/showcase/artemis-ii-trajectory.html).
+
+```{figure} ./artemis2-corot-traj.png
+  :width: 100%
+  :alt: Artemis 2 trajectory showing when the solar eclipse occurred.
+
+Visulaisation of the Artemis II trajectory with the eclipse highlighted.
+```
+
+### Moon Limb Fitting
+
+The next step is to find a known location in the image, a reference point.
+The easiest one to use for us is the center of the moon, which we find by doing edge detection and Hough filtering, using scikit-image.
+
+```python
+import numpy as np
+
+from skimage.feature import canny, peak_local_max
+from skimage.transform import hough_circle, hough_circle_peaks
+
+edges = canny(eclipse_image, sigma=2)
+
+h, w = eclipse_image.shape
+radii = np.arange(0.25*h, 0.4*h, 10)
+
+hough_res = hough_circle(edges, radii)
+accums, cx, cy, rad = hough_circle_peaks(hough_res, radii, total_num_peaks=1)
+```
+
+```{figure} ./artemis2-hough.png
+  :width: 100%
+  :alt: A cropped image of the moon showing edge detection and Hough filtering in three panes.
+
+  A cropped view of the Moon, showing the results of the canny edge detection algorithm and the Hough filter.
+```
+
+### Calculating Image Scale
+
+Based on knowing where the center of the moon is and it's radius in the image we can construct a coordinate system for the image.
+
+```python
+from astropy.coordinates import SkyCoord
+import astropy.units as u
+
+moon = SkyCoord(coords["moon"], observer=coords["artemis_ii"])
+R_moon = 0.2725076 *  u.R_earth  # IAU mean radius
+dist_moon = SkyCoord(coords["artemis_ii"]).separation_3d(moon)
+
+moon_angular_width = np.arcsin(R_moon / dist_moon).to(u.arcsec)
+im_radius = rad * u.pix
+plate_scale = moon_angular_width / im_radius
+```
+
+using this information we can build a sunpy map (see the gallery example for details), plotting this alongside the locations of the planets results in:
+
+```{figure} ./artemis2-initial-fit.png
+  :width: 100%
+  :alt: Initial coordinate system fit, showing the lunar center, limb and expected locations of Mercury, Mars and Saturn, which are offset from their positions in the picture.
+
+Initial coordinate system fit to image, notice that the locations of the highlighted planets are incorrect.
+```
+
+### Fitting Roll Angle
+
+It's clear from the previous image that the image is rotated around the center of the moon, we can solve for this rotation by using a peak finding algorithm to locate the planets in the image.
+Doing this results in a {math}`-21.2^\circ` roll angle which we can add to our Maps metadata.
-Doing this results in a {math}`-21.2^\circ` roll angle which we can add to our Maps metadata.
+Doing this results in a {math}`-21.2^\circ` roll angle which we can add to our `Map` metadata.
-Doing this results in a {math}`-21.2^\circ` roll angle which we can add to our Maps metadata.
+Doing this results in a {math}`-21.2^\circ` roll angle which we can add to our `Map` metadata.
+
+```{figure} ./artemis2-roll-fit.png
+  :width: 100%
+  :alt: Coordinate system fit with corrected roll angle, showing the lunar center, limb and expected locations of Mercury, Mars and Saturn, which match much better, but are not perfect.
+
+Coordinate system fit to image with correction for roll angle, notice that the locations of the highlighted planets are still slightly incorrect.
+```
+
+### Fitting Lens Distortion
+
+The final correction to apply to our fitted coordinate system is the distortion of the camera lens (a Nikkor AF 135mm f/2D DC).
+The lens attached to the camera the astronauts used has added some distortion to the image; objects distant from the centre of the image appear even more distant than they should.
+We can quantify exactly how much the image has been distorted through comparing the expect vs actual positions of Mars and Mercury, we add this distortion to our coordinate system and our planets now appear in the correct place.
+
+```{figure} ./artemis2-distortion-fit.png
+  :width: 100%
+  :alt: Coordinate system fit with additional correction for lens distortion, the expected positions of the planets now match the image.
+
+Coordinate system fit to with additional correction for lens distortion.
-Coordinate system fit to with additional correction for lens distortion.
+Coordinate system fit with additional correction for lens distortion.
-Coordinate system fit to with additional correction for lens distortion.
+Coordinate system fit with additional correction for lens distortion.
+```