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May 21 in spaceflight
Wikipedia records 5 spaceflight and astronomy events on May 21. Below are the pictures NASA published on May 21 in 6 different years — each one taken or released on this exact date.
Recorded events
IN THE RECORD5ENTRIES
Spaceflight and astronomy entries from Wikipedia's record of this date, oldest first — from 1932 onward.
Pictures from this date
PUBLISHED6IMAGES
NASA's Astronomy Picture of the Day for May 21, one per year. Some are public domain and some belong to the photographer — each says which.
Published on May 21
NASA’s Astronomy Picture of the Day, for this calendar date in each of the last several years.
2026
A Collision of Galaxy Clusters
This big beautiful spiral shines in X-ray light. It is about 20 times larger than our Galaxy. It belongs to Abell 2029, a galaxy cluster one billion light-years away. (To see only the galaxies, hover your cursor over the image, or follow this link.) Galaxy clusters are the largest structures in the universe that are supported by gravity. Abell 2029 is formed by thousands of galaxies, surrounded by a huge cloud of hot gas and the equivalent of hundreds of trillions times the mass of the Sun in dark matter. The spiral is made of gas, mostly hydrogen and helium, heated to tens of millions of degrees. It was found in a recent study that used data from NASA's Chandra X-ray Observatory to show that Abell 2029 had a collision with a smaller cluster four billion years ago. The collision affected the gravitational field and caused the intracluster gas to slosh, like wine moving in a wine glass, shaping the spiral.
NASA · public domain
2025
International Space Station Crosses the Sun
Typically, the International Space Station is visible only at night. Slowly drifting across the night sky as it orbits the Earth, the International Space Station (ISS) can be seen as a bright spot about once a month from many locations. The ISS is then visible only just after sunset or just before sunrise because it shines by reflected sunlight -- once the ISS enters the Earth's shadow, it will drop out of sight. The only occasion when the ISS is visible during the day is when it passes right in front of the Sun. Then, it passes so quickly that only cameras taking short exposures can visually freeze the ISS's silhouette onto the background Sun. The featured picture did exactly that -- it is actually a series of images taken a month ago from Sant Feliu de Buixalleu, Spain with perfect timing. This image series was later combined with a separate image highlighting the texture of the active Sun which included several Sun's prominences around the edge. Celestial Surprise: What picture did APOD feature on your birthday? (post 1995)
© Pau Montplet Sanz — used with the credit NASA publishes
2024
CG4: The Globule and the Galaxy
Can a gas cloud eat a galaxy? It's not even close. The "claw" of this odd looking "creature" in the featured photo is a gas cloud known as a cometary globule. This globule, however, has ruptured. Cometary globules are typically characterized by dusty heads and elongated tails. These features cause cometary globules to have visual similarities to comets, but in reality they are very much different. Globules are frequently the birthplaces of stars, and many show very young stars in their heads. The reason for the rupture in the head of this object is not yet known. The galaxy to the left of the globule is huge, very far in the distance, and only placed near CG4 by chance superposition.
NASA · public domain
2023
Tardigrade in Moss
Is this an alien? Probably not, but of all the animals on Earth, the tardigrade might be the best candidate. That's because tardigrades are known to be able to go for decades without food or water, to survive temperatures from near absolute zero to well above the boiling point of water, to survive pressures from near zero to well above that on ocean floors, and to survive direct exposure to dangerous radiations. The far-ranging survivability of these extremophiles was tested in 2011 outside an orbiting space shuttle. Tardigrades are so durable partly because they can repair their own DNA and reduce their body water content to a few percent. Some of these miniature water-bears almost became extraterrestrials in 2011 when they were launched toward to the Martian moon Phobos, and again in 2021 when they were launched toward Earth's own moon, but the former launch failed, and the latter landing crashed. Tardigrades are more common than humans across most of the Earth. Pictured here in a color-enhanced electron micrograph, a millimeter-long tardigrade crawls on moss. Your Sky Surprise: What picture did APOD feature on your birthday? (post 1995)
© Nicole Ottawa & Oliver Meckes / Eye of Science / Science Source Images — used with the credit NASA publishes
2022
Planetary Nebula Abell 7
Very faint planetary nebula Abell 7 is some 1,800 light-years distant, just south of Orion in planet Earth's skies in the constellation Lepus, The Hare. Surrounded by Milky Way stars and near the line-of-sight to distant background galaxies, its generally simple spherical shape, about 8 light-years in diameter, is outlined in this deep telescopic image. Within its confines are beautiful, more complex details enhanced by the use of narrowband filters. Emission from hydrogen is shown in reddish hues with oxygen emission mapped to green and blue colors, giving Abell 7 a natural appearance that would otherwise be much too faint to be appreciated by eye. A planetary nebula represents a very brief final phase in stellar evolution that our own Sun will experience 5 billion years hence, as the nebula's central, once sun-like star shrugs off its outer layers. Abell 7 itself is estimated to be 20,000 years old. Its central star is seen here as a fading white dwarf some 10 billion years old.
© Donald Waid — used with the credit NASA publishes
2021
Utopia on Mars
sive Utopia Planitia on Mars is strewn with rocks and boulders in this 1976 image. Constructed from the Viking 2 lander's color and black and white image data, the scene approximates the appearance of the high northern martian plain to the human eye. For scale, the prominent rounded rock near center is about 20 centimeters (just under 8 inches) across. Farther back on the right side of the frame the a dark angular boulder spans about 1.5 meters (5 feet). Also in view are two trenches dug by the lander's sampler arm, the ejected protective shroud that covered the soil collector head, and one of the lander's dust covered footpads at the lower right. On May 14, China’s Zhurong Mars rover successfully touchdown on Mars and has returned the first images of` its landing site in Utopia Planitia.
NASA · public domain
What happened on May 21
1932
Bad weather forces Amelia Earhart to land in a pasture in Derry, Northern Ireland, and she thereby becomes the first woman to fly solo across the Atlantic Ocean.
Amelia Earhart ↗
1946
While working with a mass of plutonium known as the demon core, Manhattan Project physicist Louis Slotin accidentally exposed himself to a lethal dose of hard radiation, making him the second victim of a criticality accident in history.
Plutonium ↗
1946
Physicist Louis Slotin is fatally irradiated in a criticality incident during an experiment with the demon core at Los Alamos National Laboratory.
Louis Slotin ↗
1996
The seven Trappist monks of Tibhirine who were abducted on March 27 are killed under uncertain circumstances.
Trappists ↗
2010
JAXA, the Japan Aerospace Exploration Agency, launches the solar-sail spacecraft IKAROS aboard an H-IIA rocket. The vessel would make a Venus flyby late in the year.
JAXA ↗
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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