Big Apple Sky Calendar: April, May, June 2025
In the 1990s, astronomy professor Joe Patterson wrote and illustrated a seasonal newsletter, in the style of an old-fashioned paper zine, of astronomical highlights visible from New York City. His affable style mixed wit and history with astronomy for a completely charming, largely undiscovered cult classic: Big Apple Astronomy. For Broadcast, Joe shares current monthly issues of Big Apple Sky Calendar, the guide to sky viewing that used to conclude the seasonal newsletter. Steal a few moments of reprieve from the city’s mayhem to take in these sights. As Oscar Wilde said, “we are all in the gutter, but some of us are looking at the stars.”
—Janna Levin, editor-in-chief
April
April 1
Sunrise 6:39 am EDT
Sunset 7:20 am EDT
Until the year 1582, when Pope Gregory made his famous calendar reform in all of Catholic Europe, April 1st was considered the beginning of the year. Or to purists, March 25th, the traditional date for the vernal equinox. That’s how many of the months get their names: September was the seventh month, October the eighth, November the ninth, December the tenth.
April 2
The release date, in 1968, of 2001: A Space Odyssey, a film by Stanley Kubrick and Arthur C. Clarke. Usually ranked as the greatest science fiction film of all time, and often as one of the ten best films of all time. I think I’ve seen it ten times, including the opening night in Boston, and couldn’t count the number of hours spent discussing it with friends. Clarke’s imagination and knowledge coupled with Kubrick’s subtlety and use of imagery produced an absolute masterpiece.
April 4
First-quarter moon.
April 7-8
Dates for the Northeast Astronomy Forum (NEAF) at Crowne Plaza Convention Center in Suffern, NY. This is a gigantic two-day fest of all things astronomical—primarily everything imaginable you might want to buy. In addition to big stuff (telescopes, fancy eyepieces, etc.), there are little things—calendars, ties, hats, scarves, jewelry. There will be a program of talks, too. Arrive early (as parking is limited) and bring money. It might be a good idea to call in advance, in case of rain.
April 7
On this day in 2001, the Mars Odyssey mission was launched—to search for water on Mars. This and other missions have now shown some evidence for the existence of subsurface water on Mars… and simple photography appears to show dried-up river canyons. As the Planetary Society puts it: “Mars isn’t the greatest place to quench your thirst, although it may have been a few billion years ago.”
April 10
On this day in 2019, NASA and NSF revealed the first image of a black hole—specifically, the supermassive black hole at the core of the massive galaxy M87. This was accomplished by the Event Horizon Telescope (EHT), a worldwide collaboration of radio telescopes—which agree in advance to observe the same targets at exactly the same time (and thereby simulate a telescope thousands of miles in diameter). The principle is similar, but not identical, to that which we all know as binocular vision.
April 10-12
Early on these nights, look for Venus next to the Pleiades star cluster in the evening sky. A grand view in binoculars.
April 12
Full moon. And, in 1961, the first human (Yuri Gagarin) orbits the Earth.
Mid-April
In the year 1006, one of the great supernovae in history, and the oldest in European history, was recorded in the constellation Lupus (the Wolf). Observations were reported from Europe, Africa, and China. The star was many times brighter than Venus, and remained visible throughout the year. Today it is known as SN 1006, and the ejected shell is extensively studied at radio, optical, and X-ray wavelengths. Despite the prominent shell, no central object (a compact remnant of the supernova) has ever been detected.
April 16
The Moon lies just next to Saturn in today's early morning sky.
April 20
Easter Sunday. Easter is a “moveable feast”, since it has a complex formula for its date: it falls on the first Sunday after the first full moon on or after the vernal equinox. That first full moon after the equinox occurs on April 13th, so it was “almost Easter” then. Strangely, the Orthodox church, which still uses the Julian calendar, will also celebrate Easter on April 20th this year, even though their civil calendars are far apart, having never adopted the Gregorian calendar reform.
April 24
On this day in 1990, amid much hoopla, the Hubble Space Telescope (HST) was launched. To NASA’s great embarrassment, the first images showed that the optics of the mirror were flawed—the images were fuzzy! Good for cartoonists, but bad for astronomy. Fortunately, the telescope was actually designed to be visited by astronauts… and an early visit managed to fix the flaw. For the next 33 years (and counting), the telescope has been a workhorse instrument for astronomers of all nations.
April 26
On this day in 1803, thousands of stones fell on the small French village of L’Aguile. For the preceding few decades, there had been an active debate: do “meteorites” come from the heavens (beyond the Earth), or are they some kind of terrestrial (“meteorological”) phenomenon? The young scientist Jean-Baptiste Biot traveled to the region, collected samples, interviewed eyewitnesses… and presented a convincing case: they come from space, presumably the solar system.
Individual humans and small human artifacts are mighty unlikely targets for incoming meteorites. But there are recent and well-proven cases of a human (just one) and a car (just one) being hit. They make for fun reading. Just for jollies, look them up!
April 26-30
Venus and Saturn are mighty close together in the morning sky this week. Venus is the obvious, brilliant object just above and to the right of the sunrise point.
April 27
New moon.
April 30
Sunrise 5:55 am EDT
Sunset 7:50 am EDT
Low in the west, Jupiter is just south of the waxing crescent Moon tonight. A great opportunity to see “the old Moon in the new Moon’s arms.”
May
May 1
Sunrise 5:54 am EDT
Sunset 7:51 pm EDT
May 3
In this evening’s sky, the first-quarter Moon passes just north of Mars.
May 5
In this morning’s sky (night of May 4th-5th), the Earth intersects the orbit of Halley’s Comet. The comet has been shedding debris, especially when it nears the Sun and heats up, for at least 1500 years. That debris—little dust particles—stays in orbit around the Sun. Like the character “Pig-Pen” in the Peanuts cartoons, the dust just follows the comet around. And the Earth intersects that orbit every May 4th-5th…causing a meteor shower (called the Eta Aquarids, named for the star they appear to emanate from) as the dust burns up in the atmosphere. But despite the two impressive names (“shower” and “Halley”), this shower is usually a yawner. Late April and early May mornings can be cold, and don’t usually offer much reward for the discomfort (except for one April morning in 1775). But if you happen to be stargazing this morning, you might see some meteors from that famous old comet.
May 10
Birthday of Cecilia Payne in 1900. Payne was a young student of Arthur Eddington, the English astronomer whose writing brought awareness of modern physics to the audience of astronomers (not then well trained in physics). Payne could not pursue graduate study in England (Cambridge did not grant degrees to women until 1948), so Eddington arranged for her admission to Harvard. A few years later, she produced what Otto Struve called “the most outstanding thesis the U.S.A. has ever produced.” Payne knew much more physics than most astronomers… and was able to show that the Sun was made mostly of hydrogen—an idea much doubted by astronomers at the time, since there is practically no hydrogen in the Earth’s atmosphere. She went on to a long career at Harvard, as the world’s top expert on exploding stars. When I was a young student of that subject, I had dinner with her in 1978. She was way past her prime, and I was way short of mine, but it was unforgettable.
May 12
Full moon 12:57 pm EDT.
May 8–9
On these nights, the International Space Station (ISS) makes evening overpasses of New York City. On May 8th, look generally west at 10:15 pm southeast (SE) from 9:17 to 9:23 pm EDT. On May 13th and 14th, the ISS pops up near your western horizon, passes nearly overhead, then disappears in the east five to six minutes after first appearing. First appearance is at 10:05 pm on May 13th, and 9:14 pm on May 14th. Unlike airplanes, the ISS shines with a steady light—it’s just reflecting sunlight. At 18,000 mph, it’s hard to believe where it is in space. When you first see it, it’s roughly over Kentucky; when it disappears five minutes later, it’s somewhere south of Greenland. Hundreds of satellites pass overhead every day, but only one is easily and regularly visible—it’s a metallic object half the size of a football field!
May 15
On this day in 1836, Francis Baily discovered the phenomena known as “Baily’s Beads”—the last bursts of sunlight shining through lunar valleys, visible only a few seconds before (and after) the totality phase of a solar eclipse. But remarkably, he observed it during an annular eclipse—an eclipse which just fails to be total, usually by a few percent. I hope he had good filtration! …because it can be dangerous to mess around with solar eclipses during the partial phases.
May 18
Thought to be the birthday in 1048 of Omar Khayyam, the great Persian astronomer, mathematician, and poet. Omar designed the Jalali calendar, still used today in the Middle East for religious purposes, since it’s slightly more accurate (one day error in 5000 years) than our modern Gregorian calendar (one day error in 3300 years). But he is best known for his beautiful poetry—the Rubaiyat. It has been published in many versions and many languages. In 1865 Edward Fitzgerald published an English translation which became a literary tornado, spawning hundreds of re-printings and translations into yet more languages. It even enchanted me at age 15, when my (voluntary) reading was mostly about baseball and war.
May 20
Last quarter moon, rising around midnight.
May 22
Saturn is the medium-bright object just south of the Moon tonight. But alas, it isn’t the beautiful Saturn of cartoons and photographs this year. The rings are very thin and practically edge-on, causing them to nearly disappear when seen from Earth. The rings were first discovered in 1610 by Galileo, who interpreted them as two moons (“I have observed the highest planet in triplet form”). In later years, he was amazed when they were gone (“has a mother eaten her children?”) Then a few years later, they came back!
Are these rings wobbling, like a frisbee? Nope—they maintain an essentially flat form, in the plane of Saturn’s equator. But as the Earth moves around, our viewpoint changes… and sometimes carries us into the plane of the rings. The rings are flat and wafer-thin (just ~10 meters!), so you can’t see them when they’re edge-on. That happens in February through June 2025. You’ll have to wait a few years for good ol’ Saturn to resume its beautiful telescopic appearance.
May 23-4
The waning crescent Moon passes close to Venus in the early-morning sky on these dates, for those with a clear eastern horizon.
May 26
New moon 11:06 pm EDT.
May 28
The total solar eclipse on this date in 585 BCE was perhaps the most consequential in history. According to several famous (but not necessarily independent) sources—Herodotus, Pliny the Elder, and Cicero—it stopped a long-running war between two Greek city-states, AND was predicted in advance by the Greek astronomer Thales. Most modern historians do not accept either claim, but scolding Herodotus (“The Father of History”) is usually not a good idea.
May 29
As if to challenge the ancient eclipse for pre-eminence, that of May 29th in the year 1919 is a worthy candidate. It was predicted long in advance, and the British launched an expedition, led by Arthur Eddington, to a West African island to photograph the field of stars right around the Sun during totality. Eddington had calculated how much the Sun’s gravity would bend the starlight, according to Einstein’s recently published theory of gravity (“general relativity”). Careful measurement confirmed the amount of bend predicted by Einstein’s theory. At the meeting of the Royal Society when this result was announced, it was described as the “greatest scientific achievement since Copernicus,” and the next day’s London Times was headlined “Newton’s Ideas Overthrown.”
Eddington himself, another fan of Omar Khayyam, adopted Khayyam’s classic quatrain form to describe the event at the post-conference party. It ended:
Five minutes, not a moment left to waste.
Five minutes, for the picture to be traced.
The stars are shining, and Coronal Light
Streams from the Orb of Darkness – oh, make haste!
Oh, leave the wise our measurements to collate,
One thing at least is certain, that light has weight.
One thing is certain, and the rest debate:
Light rays, when near the Sun, do not go straight!
May 30
On this day in 1971, NASA launched Mariner 9, the first spacecraft to reach and orbit Mars. Mars was the great hope for finding alien life in the solar system, and that life was the subject of many science-fiction novels. Even Tarzan (hero of the African jungle) got into the act, conquering Mars at one point. There was great excitement that year about the expected close-up photographs. The spacecraft arrived in August, and the first photos looked pretty much like the views I got through my homemade six-inch telescope. Blurry! Mars was in the grip of a planet-wide dust storm, and hardly any detail could be seen. A few weeks later, the dust subsided and we got some great photos: of a giant Martian volcano, and the first hint of long-dried-up Martian river valleys.
May 31
Sunrise 5:27 am EDT
Sunset 8:20 pm EDT
Venus is at “greatest western elongation” today, rising three hours ahead of the Sun, and appearing well up in the east near dawn. It’s a beautiful sight any morning a week before and after this date.
Mars is the medium-bright reddish object to the left of the Moon tonight. Tomorrow night (June 1st), it’s to the right of the Moon. Compared to everything else in the sky, the Moon really hustles! (The terms “right” and “left” are only appropriate for mid-northern observers, like us; “west” and “east” are better terms which work for practically any observer. From our point of view, southern observers are upside down!)
June
June 1
Sunrise 5:27 am EDT
Sunset 8:21 pm EDT
Venus is now at its maximum western elongation according to Greenwich Mean Time. Venus—the “Evening Star” of antiquity—is always close to the Sun, since it's an inner planet. Once every couple of years, it creeps into the evening sky and gets noticed by millions of people. That was true throughout the (northern) winter of 2025. Today it's 46 degrees “west” (to the right, as you look while facing east) of the Sun… and it’s the “Morning Star” which dominates the eastern sky one to two hours before sunrise—through most of May to June. You’ll find it in the east, but it’s a western elongation since it’s west of the Sun. Few people will notice it, though, since you need to be awake one to two hours before sunrise, which is mighty early in June.
The Moon is pretty close to Mars in tonight’s sky.
June 2
First quarter moon.
June 9–10
In the early morning sky on these dates, the nearly-full Moon lies just southeast of the red supergiant star Antares (Ant-ares means “rival of Mars”).
June 10
On this day in 1854, a young German mathematician gave a “job talk,” hoping to secure a faculty appointment at the university in Gottingen. His name was Georg Riemann, and he discussed what we now call “Riemannian geometry,” a system in which the normal laws of plane geometry fail. Fortunately for the future of mathematics, he got the job. Unfortunately, his life was short (he died at 39)… but his work inspired generations of mathematicians, including probably Lewis Carroll (aka the Oxford mathematician Georg Dodgson) whose famous works suggest settings in which all the familiar assumptions fail (“six impossible things before breakfast”). Albert Einstein always marveled at Riemann’s genius, and credited his discovery of Riemannian geometry as leading to his work on gravity and general relativity.
June 11
Full moon. Of course, the full moon is always opposite the Sun. And since the June Sun rises very high in the noontime sky, it follows that the full moon is now as far south (and therefore low in the sky for northerners) as it ever gets. Watch it as it just grazes those trees or buildings in your southern sky around midnight.
June 12
On this day in 1962, a rocket was launched with a detector sensitive to X-rays. Its team of scientists had previously detected X-rays from the Sun, so they figured, “why not see about the next brightest thing in the sky—the Moon?” During the five minute flight above the Earth’s atmosphere, they found X-rays, but not from the Moon. The X-rays came from a little patch of sky with nothing distinctive in it—not a planet, a galaxy, a bright star, or anything familiar. Later flights identified the source as a faint blue star with an odd spectrum. It was named Scorpius X-1, and was the subject of hundreds of papers which speculated about its nature. It turned out to be a neutron star—a tiny, solid star made entirely of neutrons. If another normal star is orbiting very close to a neutron star, gas from the companion star will get pulled by the immense gravity, and come crashing down onto the neutron star surface, producing copious X-rays. Sco X-1 was the first of many thousand such stars now known in the Galaxy.
A few years later, a similar object was discovered, called “Cygnus X-1.” It contained not a neutron star but a black hole—the first one discovered. In those days, X-ray binary stars like Cygnus X-1 received swashbuckling names. (I'm sure my black cat wasn't the only one named Cygnus.) Nowadays, these stars get names like 3XMM J004232.1+411314. Not likely to inspire any naming of beloved pets.
June 13
Birthday of Thomas Young in 1773. Young is most famous for his wave theory of light—the first to explain interference phenomena. He made many discoveries in diverse fields: vision, mathematics, Egyptology, history, music, energy, and the theory of matter. And these were just his hobbies! His main job was as a physician—a doctor—and he went to some lengths to prevent his amazing scientific work from interfering with his medical practice. With good reason, he is frequently described as “the last man who knew everything.”
June 15
Sunrise 5:24 am EDT
Sunset 8:29 pm EDT
June 18
Last quarter Moon, rising around midnight. Excellent time to scan the Moon's craters with a telescope or binoculars. The Sun is just setting over the most heavily cratered region on the Moon, creating more contrast and therefore great viewing.
June 20
Summer solstice begins at 10:40 pm EDT. Or, for “hemispheric correctness,” we can call it the June solstice—since it’s the beginning of winter in the Southern Hemisphere. The noontime Sun is high in our sky, and at the North Pole will stay in the sky continuously for three more months. At Fairbanks, Alaska, which is almost exactly on the Arctic Circle, the Sun “sets” at midnight, and “rises” a few minutes later—having just barely touched the northern horizon. So the day is essentially a 24-hour affair. Fairbanks has a golf tournament and a six mile road race (“Midnight Sun Run”) starting at midnight. At the South Pole, where the Sun disappeared on March 21st, it’s now fully dark, and that darkness will only be relieved by a little tinge of twilight starting in mid-August. (The Sun won’t actually rise there until September 23rd.)
June 22
Bertolt Brecht said it best on a large curtain which opened the Inquisition Trial scene, near the end of his play Galileo:
June 22, 1633.
A momentous date for you and me.
Of all the days, that was the one,
An age of reason could have begun.
On this day Galileo was convicted of heresy by the Roman Inquisition, and sentenced to lifetime house arrest. Brecht’s play beautifully captures the subtleties and conflicts leading up to this moment, which virtually extinguished science in Italy and much of the Catholic world for centuries (the offending book, Dialogue Concerning Two Great World-Systems, remained on the official Index of Prohibited Books until 1835). Even at the time and within the Catholic hierarchy, the controversy of the verdict was recognized. Three of the ten Inquisitors did not sign the Oath—possibly members of the Jesuit order, which supported Galileo and has always been known for scholarship (plus, more recently, basketball).
There is a story that Galileo, after guilt was pronounced and the proceedings finished, said quietly but audibly, “Eppur si muove” (“and yet it moves”), presumably referring to the Earth. In his book The Crime of Galileo, the historian Giorgio di Santillana discusses the question, and ponders if he really said it. For a man just convicted by the Inquisition, it would have been a pretty snarky comment. Di Santillana eventually concludes: maybe… but if he did, the Inquisitors “would have done their best not to hear.”
June 25
New moon 5:32 am EDT. With the Moon now effectively out of the sky, it’s a perfect time to do some summer star-gazing. The brightest parts of the Milky Way Galaxy appear in our sky any dark night from 11 pm to 3 am. Look south to see the central regions of the Milky Way, or overhead to see the Northern Milky Way (including Cygnus the Swan, and its neighbor constellations). But moonlight and city lights (especially!) are your sworn enemies in this enterprise. If you don’t manage this in late June, the new moon in late July will be just as good.
June 26
Birthday of William Thomson (aka Lord Kelvin) in 1826. Kelvin, as he is known today, became known for his temperature scale (similar to centigrade, but where 0 K = -273 deg centigrade). In his era, he was perhaps more famous for his estimate of the age of the Earth (100 million years). He reached that estimate by assuming that the Earth’s molten iron core has been cooling steadily ever since. In 1903, a young Ernest Rutherford, who discovered the enormous amount of energy locked up inside the atom’s nucleus, reported his results to the Royal Society—which showed that the Earth has been cooling off for at least one billion years. Spotting Kelvin in the front row, he was plenty nervous. But after the talk, he later recounted, “the old boy beamed at me”.
June 29
The Moon stands next to Mars in this evening’s sky.
June 30
Tunguska! On this day in 1908, a gigantic explosion occurred in a remote region of Siberia. Years later, a Russian astronomer found a newspaper clipping from 1908 which described the event while leafing through a book in a library (apparently someone had used it as a bookmark). It intrigued him, and he launched an expedition to the area, near the Tunguska River. He found a region of complete devastation. Over a radius of 20 miles, millions of trees had been knocked down in a radial pattern, and there were many skeletons of dead reindeer. These were obviously the remnants of the 1908 explosion. Interviews with local residents reported it looked like “a piece had broken off the Sun.” We still don’t know exactly what caused this event, which struck with an energy many times greater than the Hiroshima bomb. Most astronomers think it was the impact of a small comet or asteroid, which broke up as it encountered the Earth’s atmosphere (thus explaining the lack of a crater).
June 30
Sunrise 5:28 am EDT
Sunset 8:31 pm EDT ♦
Subscribe to Broadcast