The only major difference between the Sun and the stars we see at night is that the Sun is close to us, which is beneficial if you enjoy life.
Astronomers like this too, but they have another reason to rejoice in the proximity of the Sun: it allows us to see it as a disk. The sun is, of course, three-dimensional. But from afar we see it as a filled circle in the sky, which means that we can study its surface in detail, revealing it sunspots, spotlights, granules and other amazing features.
The stars in the night sky are piece further; closest to us Near Centaurusis about 280,000 times farther than the Sun! This makes it appear correspondingly smaller through a telescope—infinitely smaller, in fact, appearing as just a point of light. When an object looks like this, we say it is unresolved; when it gets big enough to have a real shape, then the problem is solved.
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Is it possible to see any other stars the same way we see our Sun, in all (or at least some) of their glory?
Well, technically yes. Although in practice it is difficult.
Telescope visual acuity depends on the size of its light-collecting holewhich is usually a mirror or lens. If you crunch the numbers, you'll find that quite a few stars in the sky appear large enough to be seen with our largest telescopes. But there is another problem: our turbulent atmosphere blurs the details of astronomical objects.
This sets a sort of limit on the minute details that can be seen in objects in the sky. But clever techniques can get around this limitation, including adaptive optics, which quickly changes the shape of a mirror in a telescope to counteract the movement of overlying air. Another technique is speckle imaging, which uses a sequence of extremely fast shutter speeds to freeze the same motion. In the 1970s astronomers have used a variation of this technique to obtain clear images of several nearby large stars.including Antares in Scorpius and everyone's favorite nascent supernova Betelgeuse in Orion. Keep in mind that although these are physically large stars, they are so far away that they appear small, less than 0.00002 degrees wide, about the same size as a US block that would appear 100 kilometers away. By comparison, the Sun is half a degree in size—more than 30,000 times larger.
As clever as these methods are, they still face a more fundamental obstacle related to the size of the aperture, which determines the resolution of the telescope. Building even larger ground-based telescopes would help, but has diminishing returns: beyond a certain size—about what we already have today—the challenge becomes incredibly difficult and expensive.
But there is another method that allows you to bypass even this limitation! This is called interferometry, and it depends on the fact that light is a wave.
Interferometric view of the red giant π.1 Gruis as seen by the PIONEER instrument on ESO's Very Large Telescope. The resolved image reveals the convective cells that make up the surface of this huge star. Each cell covers more than a quarter of the star's diameter and has a diameter of about 120 million kilometers.
Technically light is vibrations of electric and magnetic fieldsbut in most cases it still acts exactly the same as a wave. A beam of light has crests and valleys, and when two beams pass through each other, they can create interference. Peaks and troughs add up together, sometimes creating higher crests and lower troughs, and sometimes canceling each other out.
You're probably already familiar with this phenomenon, which works for other types of waves as well. If you sit in a bathtub full of water and rock back and forth rhythmically, you create waves that move up and down the length of the bathtub. When the crests of two waves pass each other, they can become so high that they splash out the bathtub water. Congratulations! You have completed difficult physics while swimming.
Starlight can also behave in the same way. Typically, interference is not as simple as interacting pairs of ridges or troughs; Starlight has multiple wavelengths, and the resulting picture it produces in any telescope is quite complex. But this structure, called interference or stripe pattern, encodes information about its stellar sourceincluding size, shape, and brightness distribution (that is, which parts are brighter or dimmer than others).
Here Very The clever part: if you have two telescopes separated by some distance, the light from both can be sent to a device that adds them together to create interference patterns that can be analyzed, decoded, and then used to create an image of the object showing its details. Critically, however, The resolution of these telescopes is determined by their distance, not their size. Two modest telescopes placed 100 meters apart could in principle see as much detail as a telescope the width of a football field!
This method is called interferometry. Astronomers have demonstrated this with radio telescopes in the 1940s and 1950sand it is now commonplace in radio observations. However, interferometry becomes more complex as the wavelength of light becomes shorter. For example, the “optical” wavelengths of visible light are much shorter than radio waves, so combining them is much more difficult. However, optical interferometry has developed with great success over the years.
One of the largest telescopes in the world. Very Large Telescope (VLT), consists of four 8.2-meter telescopes (as well as four smaller telescopes) that cover a distance of more than 100 meters, giving them phenomenal resolution. But even that's not the biggest thing: the Center for High Angular Resolution Astronomy (CHARA) array consists of six meter telescopes located a whopping 330 meters away. CHARA has a resolution better than one millionth of a degree, which is more than enough to see the features of a decent sample of stars. Actually, we have most of the allowed star images from CHARY.
Ultra-high-resolution images of stars have revealed many surprising and, frankly, strange structures. VLT looked at the red giant π1 Gruis and discovered that huge bubbles of hot gas were rising inside it. CHARA looked at the bright star Altair and saw that it was distinctly egg-shaped due to its very rapid rotation.. CHARA observations of the massive hypergiant RW Cephei showed its shape to be irregular and changing, indicating that it emitted a huge, starlight-choking cloud of dust in 2022. like Betelgeuse did in 2019.
As for Betelgeuse itself, it has been in the focus of interferometers many times. Its size has changed over the years, and it turns out that the surface is complex, churned by huge bubbles of hot gas, such as π.1 Gruis. Massive red supergiants such as Betelgeuse create most of the dust we see scattered throughout the galaxy, but the mechanism behind this phenomenon is not fully understood. Interferometric observations could help astronomers understand how this happens.
The resolution of optical interferometry is limited only by our technology and the speed at which computers can process the data. It's anyone's guess how big such a virtual telescope could become—essentially the Event Horizon Telescope, which linked radio telescopes around the world. image magnetic fields around the Milky Way's central black holeactually the size of the Earth! As our technology develops and improves, we may yet be able to see the faces of many more stars and learn from them as much as we do from our own Sun.
