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April 21 in spaceflight
Wikipedia records 2 spaceflight and astronomy events on April 21. Below are the pictures NASA published on April 21 in 6 different years — each one taken or released on this exact date.
Recorded events
IN THE RECORD2ENTRIES
Spaceflight and astronomy entries from Wikipedia's record of this date, oldest first — from 1964 onward.
Pictures from this date
PUBLISHED6IMAGES
NASA's Astronomy Picture of the Day for April 21, one per year. Some are public domain and some belong to the photographer — each says which.
Published on April 21
NASA’s Astronomy Picture of the Day, for this calendar date in each of the last several years.
2026
Three Sky Arches over Snowy Alps
Why are there three arches across the sky instead of two? Last month, after being dropped off by a helicopter at a high mountain peak in the Alps near the Swiss Italian border, an adventurous astrophotographer expected two arches of our Milky Way galaxy to be visible during the night. These were the inner arch looking in toward the center of our galaxy on the left, visible just before sunrise, and the outer arch on the right visible just after sunset. But there were three arches. The surprised astrophotographer soon realized that the sky was so dark that an entire arc of faint zodiacal light was also noticeable -- sunlight scattered by inner Solar System dust. And it artfully connected the two Milky Way arches! The next morning a helicopter picked the astrophotographer back up, and after 40 hours of processing and combining that night's images, the featured triple-arch 360-degree panorama resulted. Jigsaw Vistas: Astronomy Puzzle of the Day
© Angel Fux — used with the credit NASA publishes
2025
Galaxy Lenses Galaxy from Webb
Is this one galaxy or two? Although it looks like one, the answer is two. One path to this happening is when a small galaxy collides with a larger galaxy and ends up in the center. But in the featured image, something more rare is going on. Here, the central light-colored elliptical galaxy is much closer than the blue and red-colored spiral galaxy that surrounds it. This can happen when near and far galaxies are exactly aligned, causing the gravity of the near galaxy to pull the light from the far galaxy around it in an effect called gravitational lensing. The featured galaxy double was taken by the Webb Space Telescope and shows a complete Einstein ring, with great detail visible for both galaxies. Galaxy lenses like this can reveal new information about the mass distribution of the foreground lens and the light distribution of the background source.
NASA · public domain
2024
Perijove 16: Passing Jupiter
Watch Juno zoom past Jupiter. NASA's robotic spacecraft Juno is continuing on its now month-long, highly-elongated orbits around our Solar System's largest planet. The featured video is from perijove 16, the sixteenth time that Juno passed near Jupiter since it arrived in mid-2016. Each perijove passes near a slightly different part of Jupiter's cloud tops. This color-enhanced video has been digitally composed from 21 JunoCam still images, resulting in a 125-fold time-lapse. The video begins with Jupiter rising as Juno approaches from the north. As Juno reaches its closest view -- from about 3,500 kilometers over Jupiter's cloud tops -- the spacecraft captures the great planet in tremendous detail. Juno passes light zones and dark belts of clouds that circle the planet, as well as numerous swirling circular storms, many of which are larger than hurricanes on Earth. As Juno moves away, the remarkable dolphin-shaped cloud is visible. After the perijove, Jupiter recedes into the distance, now displaying the unusual clouds that appear over Jupiter's south. To get desired science data, Juno swoops so close to Jupiter that its instruments are exposed to very high levels of radiation.
NASA · public domain
2023
Solar Eclipse from Western Australia
Along a narrow path that mostly avoided landfall, the shadow of the New Moon raced across planet Earth's southern hemisphere on April 20 to create a rare annular-total or hybrid solar eclipse. A mere 62 seconds of totality could be seen though, when the dark central lunar shadow just grazed the North West Cape, a peninsula in western Australia. From top to bottom these panels capture the beginning, middle, and end of that fleeting total eclipse phase. At start and finish, solar prominences and beads of sunlight stream past the lunar limb. At mid-eclipse the central frame reveals the sight only easily visible during totality and most treasured by eclipse chasers, the magnificent corona of the active Sun. Of course eclipses tend to come in pairs. On May 5, the next Full Moon will just miss the dark inner part of Earth's shadow in a penumbral lunar eclipse. Total Solar Eclipse of 2023 April Gallery: Notable Submissions to APOD Watch: Planet Earth's annual Lyrid Meteor Shower
© Gwenaël Blanck — used with the credit NASA publishes
2022
Apollo 16 Moon Panorama
Fifty years ago, April 20, 1972, Apollo 16's lunar module Orion touched down on the Moon's near side in the south-central Descartes Highlands. While astronaut Ken Mattingly orbited overhead in Casper the friendly command and service module the Orion brought John Young and Charles Duke to the lunar surface. The pair would spend nearly three days on the Moon. Constructed from images (AS16-117-18814 to AS16-117-18820) taken near the end of their third and final surface excursion this panoramic view puts the lunar module in the distance toward the left. Their electric lunar roving vehicle in the foreground, Duke is operating the camera while Young aims the high gain communications antenna skyward, toward planet Earth. Celebrate: Earth Day
NASA · public domain
2021
Centaurus A's Warped Magnetic Fields
When galaxies collide -- what happens to their magnetic fields? To help find out, NASA pointed SOFIA, its flying 747, at galactic neighbor Centaurus A to observe the emission of polarized dust -- which traces magnetic fields. Cen A's unusual shape results from the clash of two galaxies with jets powered by gas accreting onto a central supermassive black hole. In the resulting featured image, SOFIA-derived magnetic streamlines are superposed on ESO (visible: white), APEX (submillimeter: orange), Chandra (X-rays: blue), and Spitzer (infrared: red) images. The magnetic fields were found to be parallel to the dust lanes on the outskirts of the galaxy but distorted near the center. Gravitational forces near the black hole accelerate ions and enhance the magnetic field. In sum, the collision not only combined the galaxies’ masses -- but amplified their magnetic fields. These results provide new insights into how magnetic fields evolved in the early universe when mergers were more common.
NASA · public domain
What happened on April 21
1964
A Transit-5bn satellite fails to reach orbit after launch; as it re-enters the atmosphere, 2.1 pounds (0.95 kg) of radioactive plutonium in its SNAP RTG power source is widely dispersed.
Transit (satellite navigation system) ↗
1972
Astronauts John Young and Charles Duke fly Apollo 16's Apollo Lunar Module to the Moon's surface, the fifth NASA Apollo Program crewed lunar landing.
John Young (astronaut) ↗
Sources and licences
Event text and thumbnails come from Wikipedia and are used under CC BY-SA 4.0. Images are drawn only from Wikimedia Commons, which does not accept non-free content — each thumbnail links to its file page, where its licence and author are recorded.
Launch records are from The Space Devs’ Launch Library 2. This archive is still being mirrored, so some days are incomplete. Pictures are NASA’s Astronomy Picture of the Day; NASA imagery is generally not subject to copyright, but individual APOD entries are frequently the property of the photographer, and each caption says which applies.
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Cosmos — Carl Sagan
Still the best single argument for why any of this matters, and it leaves the arithmetic in. For a reader who wants the science, not just the awe.
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Pale Blue Dot — Carl Sagan
The case for leaving Earth, written by someone unsentimental about how hard that is. Suits readers who want the argument rather than the poster.
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Project Hail Mary — Andy Weir
Hard-SF problem solving in The Martian's key — for anyone who liked the engineering more than the peril. The only novel on this list.
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