When looking at an object closer than 20 feet away from you (near vision), your eyes must accommodate by becoming more curved to focus on near objects properly. When looking at an object farther than 20 feet away from you (distant vision), your eyes must become less curved to focus on distant objects properly.

All elements absorb and emit specific wavelengths of light that correspond to those energy levels. An absorption spectrum is a spectrum of light transmitted through a substance, showing dark lines or bands where light has been absorbed by atoms, causing a dip in the spectrum. An emission spectrum is made by electrons falling down the energy ladder. It’s what you get when you look at hot gas, which is heated by something out of the line of sight. This heating moves the electrons up the ladder, then when they fall down the ladder some of the light they emit comes to you. This results in bright, colored spikes due to atoms releasing light at those wavelengths.

Spectroscopy is the study of the spectra produced when material interacts with or emits light. It is the key to revealing details that cannot be uncovered through a picture. A spectrograph — sometimes called a spectroscope or spectrometer — breaks the light from a single material into its component colors the way a prism splits white light into a rainbow. It records this spectrum, which allows scientists to analyze the light and discover properties of the material interacting with it. Spectroscopy is as crucial as imaging to understanding the universe.

Hubble is famous for the images captured by its cameras, but it often also relies on its spectrographs. Spectrographs collect data that tell scientists how much light comes out at each wavelength. These data reveal important details about the makeup of atmospheres on exoplanets, the compositions of stars and nebulas, the motion of galaxies and more.

Light carries information about the material with which it interacts. Different materials interact differently with light, and we can use light to understand what something is made of. All matter is made of atoms. Electrons go around the nucleus of an atom at different allowed energies, like rungs on a ladder. Light with the exact energy needed to go between rungs can be absorbed, but not others. Electrons fall down to lower rungs, emitting light at the specific energy of the difference between the rungs. This allows different atoms and molecules to emit different colors of light. Sodium’s spectrum does not look like nitrogen’s spectrum — nor like the spectrum of any other element.

The NASA Hubble Space Telescope is a project of international cooperation between NASA and ESA. AURA’s Space Telescope Science Institute in Baltimore, Maryland, conducts Hubble science operations.

The refractive power of the human eye is its ability to bend light rays as they enter the eye to focus them onto the retina at the back of the eye. This is necessary because light entering the eye is initially divergent, but the images we perceive must be clear and focused. The refractive power of the human eye is measured in diopters (D).

Hubble’s spectrographs reveal important details of many aspects of our universe. Below are examples of the many spectroscopic findings from Hubble.

The cornea is the primary refractive surface of the eye, providing approximately two-thirds of the eye's refractive power. The lens of the eye, located behind the iris, provides the remaining one-third of the eye's refractive power.

A spectrum is a rainbow! This rainbow is created when a beam of white light is broken into its component colors, such as with a prism. The colors formed are ordered according to their wavelength. When scientists look at this rainbow, they examine how intense the light is in each color. Is blue brighter than yellow, or is this specific red brighter than this other red?

A spectrograph passes light coming into the telescope through a tiny hole or slit in a metal plate to isolate light from a single area or object. This light is bounced off a special grating, which splits the light into its different wavelengths (just like a prism makes rainbows). The split light lands on a detector, which records the spectrum that is formed.

Hubble’s ultraviolet spectroscopy is one of its most powerful contributions to the astronomical community, and this capability will not be replaced or superseded by any mission in the near future. Ultraviolet spectroscopy tells us certain things about the universe, while visible and infrared spectroscopy tells us others. By combining Hubble’s ultraviolet spectroscopy with the infrared spectroscopic capabilities of the James Webb Space Telescope, the two telescopes can achieve scientific results together that neither could achieve alone.

The lens can change shape, known as accommodation, allowing the eye to focus on objects at different distances. The eye's crystalline lens is located directly behind the iris and pupil and further focuses light onto the retina. Unlike a rigid camera lens, our crystalline lenses are elastic and can change shape depending on one's vision needs for near or far objects.

When material interacts with light, properties of that material are stamped on the light. This stamp is like a specific fingerprint for each element and molecule. By examining the intensity of light in each color, scientist can work backward to infer the properties of the material, such as an object’s size, temperature, motion, and composition, that touched the light along the way.

Light rays enter the eye through the cornea, a transparent dome-shaped tissue that is the eye's outermost layer. The cornea bends or refracts, light rays traveling to the pupil. The shape of the cornea determines how much of the light is bent and whether the image will be focused correctly on the retina at the back of the eye. Once the light has passed through both refraction layers, it converges into a single focal point onto a small area. This is where photoreceptors start transforming visible photons into electrical signals sent along nerve fibers up to your brain for interpretation – ultimately resulting in what is known as sight.

The amount of bend or curve placed upon incoming light rays depends on one's refractive power index: The higher power index means more curvature required of incoming light, and vice versa. People with myopia (nearsightedness) have too much anatomical curvature in their eyes. This causes incoming light to focus too soon before reaching the retina, causing blurry vision when looking at distant objects. Inversely, people with hyperopia (farsightedness) have anatomical curvature that is too slight in their eyes. This causes incoming light rays to not bend enough before reaching their retinas and, as a result, causes blurry vision when looking at nearby objects.