Big Apple Sky Calendar: April 2023

Dramatic highlights from the skies above Earth by intrepid astronomer Joe Patterson.
Annular solar eclipse on May 20, 2012, in Bluit, New Mexico.Photo: Kevin Baird via Flickr.

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 1

Sunrise 6:39 am EDT

Sunset 7:20 pm 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 6

Full moon 12:36 am EDT.

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.”

A colored photo of a canyon on the surface of Mars
Mosaic image of Valles Marineris—colored to resemble the martian surface—from the Thermal Emission Imaging System (THEMIS) on NASA’s Mars Odyssey orbiter. Visible faulting suggests there were once paths for subsurface water to escape.Photo: NASA/JPL.

April 9

Easter Sunday. Easter is a “moveable feast” holiday, because it is pegged to the full moon, rather than a calendar date (“first Sunday after the first full moon on or after the vernal equinox”).

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.

EHT photo of the black hole M87
EHT photo of the M87 black hole.Photo: Event Horizon Telescope Collaboration.

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

In 1961: First human (Yuri Gagarin) to orbit the Earth.

Two astronauts in a bus
Yuri Gagarin on the bus on the way to the launch of Vostok 1. The cosmonaut behind Gagarin is German Titov, the back-up pilot who became pilot of Vostok 2.Photo: NASA.

April 13

Last quarter Moon, rising around midnight.


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.

False-color X-ray image of SN 1006 supernova remnant
The hot remains of a 1,000-year-old supernova, or its remnants, about 7,000 light years from Earth. Captured in false-color by NASA's Chandra X-ray Observatory.Photo: NASA/CXC/Middlebury College/F.Winkler.

April 15-16

On these two days, the Northeast Astronomy Forum (NEAF) will be held at Rockland Community College. Imagine a large gymnasium full of the latest stuff from just about every vendor roughly connected with astronomy (telescopes, toys, clothing, books, etc.). I recommend calling the organizers (the Rockland Astronomy Club) to make sure it'll proceed as scheduled.

April 16

The Moon lies just next to Saturn in today's early morning sky.

April 20

At 11:15 pm EDT on this night the new Moon stages an annular-total eclipse of the Sun. This is a strange blend of eclipse types: wherever it's total, it's just BARELY total—because the angular size of Sun and Moon are almost exactly the same. Also called a “hybrid” eclipse. But as you might guess from the timing of this rare event (near midnight EDT), it occurs on the wrong side of the Earth for us. Basically an Asia-Australia event.

April 22-3

On these nights, watch the thin-crescent Moon pass Venus in the early evening sky. Good nights for viewing/photographing “the old Moon in the new Moon's arms.”

Earthshine on May 14, 2007.Photo: jpstanley via Flickr.

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.

Two images of galaxies, one blurry and one clear
Comparison image of the core of the galaxy M100 showing the dramatic improvement in HST's view of the universe after the first Hubble Servicing Mission in December 1993. The first image was taken on November 27, 1993, and the second on December 31, 1993.Photo: NASA/HST.

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 27

First quarter Moon.

April 30

Sunrise 5:55 am EDT

Sunset 7:50 pm EDT ♦

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