The Lycurgus Cup is a Roman-era glass goblet that changes color from jade green to ruby red depending on if a light is shining on its front or back. But experts are unsure where the cup was found, where it was made, or whether the glassblower who made it created the color-changing effect on purpose.

In 1958, the British Museum acquired the cup from the Rothschild banking family, which had owned the artifact since the mid-19th century. Known colloquially as the Lycurgus Cup for its depiction of the mythical king who angered the god Dionysus, the glass is about 6.3 inches (15.9 centimeters) tall and weighs around 1.6 pounds (700 grams).

The glass is a remarkably well-preserved example of a Roman "cage-cup," according to a 1959 study of the artifact by archaeologists D. B. Harden and Jocelyn Toynbee. Only a handful of cage-cups still exist, and experts believe the goblets were made by cutting and grinding decoration into thick glass. Because small bridges were left to ensure the decoration remained on the glass, the overall effect is like a cage. Harden and Toynbee estimated that the Lycurgus Cup was manufactured in the fourth century, likely in Italy, but they noted that the bronze frame that forms the stem and rim of the goblet is probably a 19th-century addition.

Depicted on the cup is the myth of the punishment of Lycurgus, king of the Thracian tribe called the Edoni (also called the Edonians). Lycurgus did not approve of the worship of Dionysus and banished the god into the sea with an ax. But one of Dionysus' priestesses, Ambrosia, decided to fight Lycurgus. Ambrosia changed herself into a vine and wound herself around Lycurgus, who was unable to escape. The other priestesses thronged around them and tormented Lycurgus. Given that Dionysus was a god of wine and merriment, the depiction of Lycurgus' punishment may have been particularly appropriate for this goblet. Additionally, the change in color from green to red may have been meant to mimic the ripening of grapes on the vine.

Color-changing cups, also called dichroic cups, were mentioned in ancient Roman historical records. For example, a second-century letter possibly penned by Emperor Hadrian to his brother-in-law mentions a gift of two dichroic cups to use during banquets. But very few fragments of this mysterious type of glass survive today, a 2007 study noted.

For decades, experts have been working out how ancient Romans produced dichroic cups, and some have even replicated the Lycurgus Cup's color-changing effect. A 1963 study confirmed that the key seems to be the addition of microscopic nanoparticles of gold and silver during glassblowing that produce the appearance of milky-green glass when lit from the front and nearly translucent red glass when lit from behind. The metal nanoparticles are smaller than grains of sand and interact with light, creating the perception of a color change.

A replica of dichroic glass made by Corning Glassworks in the 1960s went from green to amethyst in the light, the 2007 study reported, and in 2020, researchers included silver and gold nanoparticles in 3D printing to replicate the color-changing properties of the glass.

More recently, experts at the University of Sheffield in the U.K. reproduced the dichroic glass by reverse-engineering the "recipe" from the original Lycurgus Cup. The team then commissioned a glass artist to create a Lycurgus-inspired design from the replica.

But because so few examples of dichroic glass exist, experts are still unsure whether Roman artisans created the color-changing effect on purpose or whether traces of gold, which would have been available in an ancient craft studio, slipped into the molten glass and made a rare and unusual material that mystified even the most skilled glassblowers.

For more stunning archaeological discoveries, check out our Astonishing Artifacts archives.

Birdman Copper Plate

Inuit Carving of a Norseman

Maya Death Urn

Can you put together last week's Astonishing Artifact?

'> Lycurgus Cup: A Roman glass goblet made with ancient color-changing nanotechnology stunning new images from the Hubble and James Webb space telescopes.

Rising from the cloudy Carina Nebula some 7,500 light-years from Earth, the Cat's Head Nebula is a column of star-sculpted gas and dust that vaguely resembles a feline sitting with its back to us, coyly turning its head to show off a single red eye. That eye is a young star that's embedded deep within the dust and possibly transforming it before our eyes.

Nebulas like these occur when the radiation from active young stars lights up and erodes the material around them. They are beautiful and easy to find; if this cosmic cat gets bored staring at us, it can just waltz over to the other side of the Carina Nebula and crawl into a similar globule of gas that looks exactly like a box with an open lid. (Cats will be cats, after all.)

In honor of Halloween, the European Space Agency (ESA) shared three competing views of the Cat's Head Nebula — one from the Hubble Space Telescope, which captures optical light, and two from the infrared instruments aboard the James Webb Space Telescope (JWST). The three views, shown below, reveal different features of the nebula in different wavelengths of light, getting progressively spookier as more color drains out of the scene.Take a look at all three images — and cast your vote for the spookiest in the poll at the end.

Hubble's view

Observing the nebula in the same visible wavelength range that you could see through a strong backyard telescope, Hubble highlights the dark pillar of dust that has survived the ultraviolet assault of nearby stars. The wispy edges at the right of the column show where starlight is evaporating the gas around it, slowly whittling it away to nothing.

The glow of blue, yellow, orange and red light around the dust pillar mark where starlight is interacting with different gas molecules, including oxygen, hydrogen and sulfur, according to ESA. The process is similar to how different molecules in Earth's atmosphere produce different-colored auroras when excited by solar radiation — just on a much grander scale.

JWST's near-infrared view

Switching to light human eyes cannot see, JWST's Near-Infrared Camera cuts through the wispier outer layers of dust to show the densest material at the column's center. Countless additional stars and galaxies appear in the field of view as their infrared glow penetrates the surrounding material.

Here we see a more complex, turbulent column, showing how stellar radiation is carving up the inside of the cat's head as well as its edges. JWST's view also illuminates a disembodied, hand-like structure to the left of the cat, reaching out as if to pet its cosmic companion.

JWST's mid-infrared view

The final view, taken with JWST's Mid-Infrared Instrument, cuts to the ghostly core of the nebula, showing little more than smoky, bluish light. According to ESA, these are the emissions of molecules called polycyclic aromatic hydrocarbons — typically colorless molecules of carbon and hydrogen related to combustion.

While most starlight disappears in this view, a strange new bright spot emerges to the right of the cat's head. This orange speck is a true mystery, according to ESA, and its relationship to the rest of the nebula is unknown.

'> Hubble and Webb spot something ghostly happening in the Cat's Head Nebula

Given that the hemispheres are symmetric about the equator, you may think that, on both sides of the world, summers should be similar – both in terms of their climate and factors like their length. But are Northern and Southern hemisphere summers really the same?

Climate experts tell Live Science that they differ quite a bit — and that comes with a clear recommendation for sun enthusiasts.

The most obvious difference is that Northern and Southern summers happen at different times. According to NASA, this arises because Earth's axis is tilted 23.4 degrees relative to the plane of our planet's orbit around the sun.

This tilt causes the Northern and Southern hemispheres to be oriented toward the sun at different times throughout the year. Between the Northern Hemisphere's summer solstice and autumnal equinox, the Northern Hemisphere is oriented toward the sun, resulting in summer, and vice versa in the Southern Hemisphere.

This means that summers between the Northern and Southern hemispheres sit six months out of sync with each other — with Northern summers spanning late June to late September and Southern ones going from late December to late March. (Summers are also defined meteorologically, or relative to changes in weather phenomena, as being the hottest months of the year. Under this definition, Northern summers run from June to August, and Southern ones go from December to February.)

Northern summers are longer

Another difference between Northern and Southern summers is their duration. According to NASA, Northern Hemisphere summers are, on average, 4.5 days longer than Southern Hemisphere summers. (This is with respect to the astronomical definition; meteorologically, Northern summers are longer than Southern ones by two days in non-leap years, but this is due to February being the calendar's shortest month.)

The 4.5-day difference occurs because Earth's orbit around the sun is slightly elliptical instead of perfectly circular, according to NASA. Consequently, Earth's orbital velocity (the speed at which our planet hurtles around the sun) isn't constant.

During the Northern Hemisphere's summer, Earth is farther away from the sun and thus moving more slowly, said Georg Feulner, a senior researcher at the Potsdam Institute for Climate Impact Research in Germany. This is due to Kepler's second law of planetary motion, he added.

This means that at aphelion ‪(the point at which our planet is farthest from the sun)‬ Earth is traveling at 18.2 miles per second (29.3 kilometers per second). This jumps to 18.82 miles per second (30.29 km/s) at perihelion ‪(the point when Earth is closest to the sun ) which occurs during Southern summers.

While this may seem like a tiny difference in speed, it causes our planet's path around the sun to be 53,686 miles (86,400 kilometers) shorter in a 24-hour-interval at aphelion compared with at perihelion. In other words, Earth covers more "ground" at aphelion than at perihelion over a 24-hour-interval. "Therefore, the time between the Northern Hemisphere spring and autumn equinoxes is longer than the time between the Southern Hemisphere spring and autumn equinoxes, Feulner told Live Science in an email.

Northern summers are hotter

A third point of difference is that Northern summers are typically hotter than Southern ones. A 2015 study in the journal Climate Dynamics showed the precise value of this depends on whether temperatures are measured on the surface air, land or ocean, and the latitude at which they're taken. Nonetheless, when averaged over all domains and latitudes, Northern summers are 7.83 degrees Fahrenheit (4.35 degrees Celsius) hotter than Southern ones.

So what's behind this? Earth's changing distance from the sun isn't important. If it were, Earth's aphelion crossing during Northern summers should make them cooler than Southern summers during the perihelion crossing. Instead, several other factors are responsible.

One is the Northern Hemisphere's bigger fraction of land compared to its large water bodies like oceans. "Land has a lower heat capacity than water and so increases temperature more for a given heating than water does," Richard Seager, a professor at Columbia University's Lamont-Doherty Earth Observatory, told Live Science in an email. As a result, the many inland sites in the Northern Hemisphere heat up rapidly and have higher summer temperatures, according to the UCAR Center for Science Education.

Additionally, Seager said, another difference lies in the way heat is distributed through air and water. The solar heat that land receives warms only the first few feet of the atmosphere, while the heat water absorbs gets mixed throughout its depths. This makes the Southern Hemisphere — with its larger fraction of water — cooler over summer.

The second factor for the North Hemisphere's higher summer temperatures are cross-equatorial ocean currents. Such currents cross the equator, transferring water and heat between the hemispheres. The primary current is the Atlantic Meridional Overturning Current (AMOC). "The AMOC transports heat from the SH [Southern Hemisphere] to the NH in the Atlantic," Feulner said. This warms Northern oceans and seas, which, in turn, heats up adjacent land-masses.

So, Northern Hemisphere summers are longer and hotter than Southern ones. If you want to stretch out your summer, you now know where to go.

How much do you know about our blue planet? Test your terran knowledge with our Earth quiz!

'> How do summers differ between Earth's hemispheres?