Deep-sky objects may appear static throughout our lifetime but by carefully “blinking” archival and current images we can discern real changes in their appearance.

Nova Persei expansion
Debris blasted from the 1901 explosion of Nova Persei continues to expand outward to this day and makes an ideal subject for time-lapse photography (see below). This mosaic image contains X-ray data from Chandra (blue), optical data from NASA's Hubble Space Telescope (yellow), and radio data from the Karl G. Jansky Very Large Array (pink).
X-ray: NASA / CXC / RIKEN /D. Takei et al; Optical: NASA / STScI; Radio: NRAO / VLA

Amateur astronomers are constantly aware of the passage of time from the split-second disappearance of a star occulted by the Moon to the trillions of years it takes for the Sun to evolve from black dust to black dwarf. We so often rub shoulders with ancient things we're keenly aware of time's wide spectrum and the tiny slot we occupy called now. Regrettably, we can't be around long enough to witness changes on a vast scale but have a good sense of what has been and will be by blending what science has revealed with happy hours under the star-specked sky.

M3 variable stars
In this time-lapse animation of the globular cluster M3 taken at 3:47 and 6:18 UT on April 10, 2023, you can clearly see changes in the light of 14 different variable stars. Red lines point to stars that are brightening; those marked in blue are dimming. M3 is rich in variable stars the majority of which are RR Lyrae stars with periods as short as a few hours.
Tom Polakis

Variable stars, novae, supernovae, and a small number of double and large-proper-motion stars (e.g., Barnard's Star) show changes within the scope of a human lifetime. The rest of the universe is essentially a series of still-life paintings. The Andromeda Galaxy looks the same to my floater-filled eyes today as it did during my clear-eyed youth. Just about everything is too far away and evolves too slowly for the human eye to grasp. What I wouldn't give to live to be a million years old — and keep my health (and health coverage). That would be enough time to see wholesale changes in the outlines of the constellations, star clouds ripen into stars, and maybe even a stunning Milky Way supernova.

Crab Nebula animation
Amateur astronomer Detlef Hartmann created this amazing back-and-forth animation of the expanding Crab Nebula by photographing it each year from 2008 through 2022 in a 17.4-inch telescope. The supernova remnant is currently expanding outward at around 1,500 kilometers per second (more than 3.3 million miles per hour). Its angular size increases by about 0.21″ per year.
Detlef Hartmann

Wishful thinking aside, we can use time-lapse photography to see how a few cosmic objects have changed in the past 100-plus years and in a few cases in even less time. Changes in the structure of planetary nebulae, emission and reflection nebulae, supernova remnants, and novae debris clouds are all fair game. Several of these then-and-now videos use Hubble Space Telescope imagery. Amateur astronomers have created others, including several superb examples by Tom Polakis, observer and research assistant at Lowell Observatory. Polakis has created a time-lapse gallery of deep-sky objects, variable stars, and supernovae by melding old and new images into animated gifs that reveal real changes in their appearance. It's not an easy process.

Trifid Nebula expansion
This animation switches between an image of the Trifid Nebula (M20) taken in 1921 by John Duncan with the 100-inch Mt. Wilson telescope and one made by Tom Polakis in 2023. Red arrows point to changes in the nebula's structure. Yellow arrows indicate stars with large motions across our line of sight. "Much of the difference between the images is due to how they were acquired (filter, site, etc.), but some real motions are visible," said Tom Polakis who created the time-lapse. North is at left.
Tom Polakis (2023), John Duncan (1921) / Carnegie Institution
NGC 7293 time-lapse
Images made in 1914 by H. D. Curtis with the 36-inch Crossley reflector at Lick Observatory and Tom Polakis in 2015 show the expansion of the planetary nebula NGC 7293, better known as the Helix Nebula. The object lies 655 light-years away. The inner disk is expanding at 40 kilometers per second and the outer ring at about 32 km/s. Notice also that the entire nebula is drifting across our line of sight as evidenced by all of the stars sliding back and forth.
H.D. Curtis (1914), Tom Polakis (2015)

"The alignment can be difficult, even with software that uses multiple stars," said Polakis. "But what is more difficult is balancing brightness levels and sharpness in the image pairs. The worse image of the two is the lowest common denominator that I try to somewhat match by adjusting histogram levels and sometimes even blurring the better image."

First photo Orion Nebula
Physician and amateur astronomer Henry Draper used an 11-inch Alvan Clark refractor and 50-minute exposure to take the first photo of the Orion Nebula on September 30, 1880.
Henry Draper

Planetary nebulae typically expand at the rate of around 40 kilometers per second (94,000 miles/hour) and supernovae remnants at (initially) 10,000 kilometers per second (22.4 million miles/hour). This makes them good targets for detecting expansion and other structural changes over nearly a century and a half. Time-lapses also reveal changes in the brightness levels and positions of small cloudlets in emission nebulae. The cameras started rolling when amateur astronomer Henry Draper took the first deep-sky photo in 1880 of the Orion Nebula, and images have been pouring in ever since.

Hind's Variable Nebula changes
Six years is all it took to reveal dramatic changes in the appearance of the reflection nebula NGC 1555 (Hind's Variable Nebula), which is illuminated by the 10th-magnitude variable star T Tauri. Located about 470 light-years away, changes in the nebula's appearance occur due to variations in the star's light.
Tom Polakis
Orion Nebula time-lapse
Although the exposure and level of detail between these two images of the Orion Nebula differ, this pair of images taken 118 years apart shows subtle changes in the nebula's contours. Several speedy line-of-sight stars also jump out. A prominent one appears in dark nebulosity to the upper left of the bright central region.
George Ritchey (1901), Tom Polakis (2019)

The creators of these stunning animations have done their best to equalize variations in exposure and equipment. I hope you find them as eye-opening as I did. Be sure to visit Tom's gallery to revel in more. Until we've figured out the secret to immortality these compressed views reveal a universe of continual change. Of course, we knew that, but to see it is quite another thing.

In 2002 a previously unremarkable star in Monoceros erupted in a massive blast to briefly became one of the brightest stars in the Milky Way. Dubbed V838 Monocerotis, the flash of light it emitted reflected off nearby dust creating an expanding "light echo." This time-lapse, made with images from the Hubble Space Telescope, beautifully captures the echo's evolution between 2002 and 2006. The cause of the outburst may have been the merger of two stars in a triple-star system.
The Hubble Space Telescope's fine resolution reveals changes in the filaments of the Veil Nebula supernova remnant between 1997 and 2015. The Veil, located in Cygnus, is the expanding remains of a star that exploded as a supernova maybe as long as 20,000 years ago. Today the fragments continue to expand into space at some 415 kilometers per second (929,000 miles per hour). To loop this and other YouTube videos right-click on the image and select the loop option.
Nova Persei 1901 appeared in February 1901 and quickly rose to magnitude 0 to become one of the brightest novae of the 20th century. A nova occurs when a white dwarf star draws material (mostly hydrogen) from a closely orbiting companion. The gas accumulates on the dwarf's surface, where it becomes compressed and heated until it explodes, blasting the outer layers of the star into space to form an expanding cloud of debris. Various telescopes captured Nova Persei's debris cloud in the video from 1953 to 2011. Today the nova is known as GK Persei and still "tosses in its sleep." It undergoes modest eruptions every few years when it brightens from magnitude 13 to around 10. Use this AAVSO chart to pinpoint its location and estimate its brightness.
Liimets et al. (Astrophysical Journal Vol. 761, p. 34, 2012) and AAS
Deep-sky time-lapse maps
There's no better time than the present to take a look at a mid-summer selection of our featured objects. Clockwise from left: M3, M20, the Veil Nebula, NGC 7293, and GK Persei.


Image of Martian-Bachelor


July 15, 2023 at 12:31 am

I first saw one of these several years ago. I can't recall the guy's name but he'd taken a scan of the POSS Sky Survey photo of the Crab Nebula (from the 1950s) and paired it with an image he'd made recently with a small scope. The six decade or so interval was amazing in showing the expansion.

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Image of Yaron Sheffer

Yaron Sheffer

July 20, 2023 at 9:31 am

Way cool! M1 looks like a beating heart. With stunning swirling motions around the pulsar. Can’t wait to see a time lapse of M31 or M51 or M81 or M101 rotating 😉

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