Every once in a rare while, one of our inner planets transits across the face of the Sun. Over the last few years, the Helioseismic and Magnetic Imager on NASA's Solar Dynamics Observatory has observed both inner planets transit across the Sun.
On November 11, 2019, Mercury made such a transit. Mercury also transited the Sun on May 9, 2016. The images below show Mercury's 2019 transit (left; created with mercury_composite_2019.ipynb) and 2016 transit (right; created with mercury_composite.ipynb) as captured by the Helioseismic and Magnetic Imager instrument aboard NASA's Solar Dynamics Observatory. Both images show the position of Mercury every 21 minutes (except for the egress point). The 2019 image shows a much faster transit, at 5.5 hours instead of 2016's 7.5-hour transit, due to the change in the distance between the Earth and the Sun.
On May 9, 2016, two different instruments observed the transit of Mercury from two different vantage points: the Solar Dynamics Observatory (left) in an inclined geosynchronous orbit, and the Solar and Heliospheric Observatory (right) in a halo orbit around the Earth-Sun L1 Lagrangian point. The notebook titled mercury_composite.ipynb creates both of the images below.
On June 6, 2012, Venus transited the face of the Sun. The transit obscured some of the sunlight we observe here on Earth, causing a dip in the brightness of the Sun. People who observe other stars look for a similar signal to indicate the presence of an extrasolar planet. The notebook titled venus_transit.ipynb creates images to make a movie of the transit of Venus.