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NASA Astronomy Picture of the Day:

It's only 50 light-years to 51 Pegasi. That star's position is indicated in this snapshot from August, taken on a hazy night with mostly brighter stars visible above the dome at Observatoire de Haute-Provence in France. Twenty-six years ago, in October of 1995, astronomers Michel Mayor and Didier Queloz announced a profound discovery made at the observatory. Using a precise spectrograph they had detected a planet orbiting 51 Peg, the first known exoplanet orbiting a sun-like star. Mayor and Queloz had used the spectrograph to measure changes in the star's radial velocity, a regular wobble caused by the gravitational tug of the orbiting planet. Designated 51 Pegasi b, the planet was determined to have a mass at least half of Jupiter's mass and an orbital period of 4.2 days, making it much closer to its parent star than Mercury is to the Sun. Their discovery was quickly confirmed and Mayor and Queloz were ultimately awarded the Nobel Prize in physics in 2019. Now recognized as the prototype for the class of exoplanets fondly known as hot Jupiters, 51 Pegasi b was formally named Dimidium, latin for half, in 2015. Since its discovery, over 4,000 exoplanets have been found.

Photo by Josselin Desmars

NASA Astronomy Picture of the Day:

This pretty starfield spans about three full moons (1.5 degrees) across the heroic northern constellation of Perseus. It holds the famous pair of open star clusters, h and Chi Persei. Also cataloged as NGC 869 (top) and NGC 884, both clusters are about 7,000 light-years away and contain stars much younger and hotter than the Sun. Separated by only a few hundred light-years, the clusters are both 13 million years young based on the ages of their individual stars, evidence that they were likely a product of the same star-forming region. Always a rewarding sight in binoculars, the Double Cluster is even visible to the unaided eye from dark locations. But a shroud of guitar strings was used to produce diffraction spikes on the colorful stars imaged in this vibrant telescopic view. Global Moon Party: Including APOD's Best Moon Images: Saturday, October 9

Photo by Jack Groves

NASA Astronomy Picture of the Day:

Slide your telescope just east of the Lagoon Nebula to find this alluring field of view in the rich starfields of the constellation Sagittarius toward the central Milky Way. Of course the Lagoon nebula is also known as M8, the eighth object listed in Charles Messier's famous catalog of bright nebulae and star clusters. Close on the sky but slightly fainter than M8, this complex of nebulae was left out of Messier's list though. It contains obscuring dust, striking red emission and blue reflection nebulae of star-forming region NGC 6559 at right. Like M8, NGC 6559 is located about 5,000 light-years away along the edge of a large molecular cloud. At that distance, this telescopic frame nearly 3 full moons wide would span about 130 light-years. Global Moon Party: NASA's Night Sky Network: Saturday, October 9

Photo by Roberto Sartori

NASA Astronomy Picture of the Day:

Where do the dark streams of dust in the Orion Nebula originate? This part of the Orion Molecular Cloud Complex, M43, is the often imaged but rarely mentioned neighbor of the more famous M42. M42, seen in part to the upper right, includes many bright stars from the Trapezium star cluster. M43 is itself a star forming region that displays intricately-laced streams of dark dust -- although it is really composed mostly of glowing hydrogen gas. The entire Orion field is located about 1600 light years away. Opaque to visible light, the picturesque dark dust is created in the outer atmosphere of massive cool stars and expelled by strong outer winds of protons and electrons.

Photo by Jari Saukkonen

NASA Astronomy Picture of the Day:

Sunrise at the South Pole is different. Usually a welcome sight, it follows months of darkness -- and begins months of sunshine. At Earth's poles, it can take weeks for the Sun to rise, in contrast with just minutes at any mid-latitude location. Sunrise at a pole is caused by the tilt of the Earth as it orbits the Sun, not by the rotation of the Earth. Although at a pole, an airless Earth would first see first Sun at an equinox, the lensing effect of the Earth's atmosphere and the size of the solar disk causes the top of the Sun to appear about two-weeks early. Pictured two weeks ago, the Sun peeks above the horizon of a vast frozen landscape at Earth's South Pole. The true South Pole is just a few meters to the left of the communications tower. This polar sunrise capture was particularly photogenic as the Sun appeared capped by a green flash.

Photo by Martin WolfU. WisconsinIceCube Neutrino Obs.NSFhtAlice Allen

NASA Astronomy Picture of the Day:

These two mighty galaxies are pulling each other apart. Known as the "Mice" because they have such long tails, each spiral galaxy has likely already passed through the other. The long tails are created by the relative difference between gravitational pulls on the near and far parts of each galaxy. Because the distances are so large, the cosmic interaction takes place in slow motion -- over hundreds of millions of years. NGC 4676 lies about 300 million light-years away toward the constellation of Bernice's Hair (Coma Berenices) and are likely members of the Coma Cluster of Galaxies. The featured picture was taken with the Hubble Space Telescope's Advanced Camera for Surveys in 2002. These galactic mice will probably collide again and again over the next billion years so that, instead of continuing to pull each other apart, they coalesce to form a single galaxy. Follow APOD in English on: Facebook, Instagram, or Twitter

NASA Astronomy Picture of the Day:

Sure, you can see the 2D rectangle of colors, but can you see deeper? Counting color patches in the featured image, you might estimate that the most information that this 2D digital image can hold is about 60 (horizontal) x 50(vertical) x 256 (possible colors) = 768,000 bits. However, the yet-unproven Holographic Principle states that, counter-intuitively, the information in a 2D panel can include all of the information in a 3D room that can be enclosed by the panel. The principle derives from the idea that the Planck length, the length scale where quantum mechanics begins to dominate classical gravity, is one side of an area that can hold only about one bit of information. The limit was first postulated by physicist Gerard 't Hooft in 1993. It can arise from generalizations from seemingly distant speculation that the information held by a black hole is determined not by its enclosed volume but by the surface area of its event horizon. The term "holographic" arises from a hologram analogy where three-dimension images are created by projecting light through a flat screen. Beware, some people staring at the featured image may not think it encodes just 768,000 bits -- nor even 2563,000 bit permutations -- rather they might claim it encodes a three-dimensional teapot.

NASA Astronomy Picture of the Day:

Posing as a brilliant evening star, Venus lies near the western horizon in this southern hemisphere, early spring, night skyscape. To create the composite view exposures tracking the sky and fixed for the foreground were taken on September 25 from Cascavel in southern Brazil. In view after sunset, Venus appears immersed in a cone of zodiacal light, sunlight scattered from dust along the Solar System's ecliptic plane. In fact from either hemisphere of planet Earth, zodiacal light is most visible after sunset near a spring equinox, (or before sunrise near an autumn equinox) when its luminous arc lies at steep angles to the horizon. Extending above the sunset on this night, the zodiacal light reaches toward rich starfields and immense interstellar dust clouds in the bulge of the central Milky Way. Follow along the Milky Way from the central bulge back toward the horizon and you'll spot the closest star system to the Sun, Alpha Centauri, a mere 4.37 light-years away.

Photo by Rodrigo Guerra

NASA Astronomy Picture of the Day:

Dark markings and colorful clouds inhabit this stellar landscape. The deep and expansive view spans more than 30 full moons across crowded star fields toward the center of our Milky Way Galaxy. Cataloged in the early 20th century by astronomer E. E. Barnard, the obscuring interstellar dust clouds seen toward the right include B59, B72, B77 and B78, part of the Ophiuchus molecular cloud complex a mere 450 light-years away. To the eye their combined shape suggests a pipe stem and bowl, and so the dark nebula's popular name is the Pipe Nebula. Three bright nebulae gathered on the left are stellar nurseries some 5,000 light-years distant toward the constellation Sagittarius. In the 18th century astronomer Charles Messier included two of them in his catalog of bright clusters and nebulae; M8, the largest of the triplet, and colorful M20 just above. The third prominent emission region includes NGC 6559 at the far left. Itself divided by obscuring dust lanes, M20 is also known as the Trifid. M8's popular moniker is the Lagoon Nebula.

Photo by Gabriel Rodrigues Santos

NASA Astronomy Picture of the Day:

Gorgeous spiral galaxy M33 seems to have more than its fair share of glowing hydrogen gas. A prominent member of the local group of galaxies, M33 is also known as the Triangulum Galaxy and lies a mere 3 million light-years away. Sprawling along loose spiral arms that wind toward the core, M33's giant HII regions are some of the largest known stellar nurseries, sites of the formation of short-lived but very massive stars. Intense ultraviolet radiation from the luminous massive stars ionizes the surrounding hydrogen gas and ultimately produces the characteristic red glow. To highlight the HII regions in this telescopic image, broadband data used to produce a color view of the galaxy were combined with narrowband data recorded through a hydrogen-alpha filter, transmitting the light of the strongest hydrogen emission line. Close-ups of cataloged HII regions appear in the sidebar insets. Use the individual reference number to find their location within the Triangulum Galaxy. For example, giant HII region NGC604 is identified in an inset on the right and appears at position number 15. That's about 4 o'clock from galaxy center in this portrait of M33.

Photo by Luca Fornaciari

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