4.4 KiB
| name | created_by | created_date | updated_by | updated_date |
|---|---|---|---|---|
| Ursa Major | skybber | 2021-08-01 07:43:10.609963 | skybber | 2022-02-12 08:56:18.712109 |
The Big Dipper is one of the oldest and perhaps most famous constellations today, featuring a striking pattern of seven bright stars called the Big Dipper. In the older conception, only the part of the constellation consisting of the seven main stars α (1.79mag), β (2.37mag), γ (2.44mag), δ (3.31mag), ε (1.77mag ), ζ (2.09mag), η (1.86mag) Ursa Maioris was considered to be the Big Dipper, and the constellation as a whole is referred to in almost all languages as the Big Dipper, after the Latin name Ursa Maior. Today, we often see the common name of the Big Dipper, but it refers to the entire constellation. In "modern" America, the figure is known as the Great Dipper. The conspicuous grouping of the Great Dipper is not entirely by chance such an arrangement of individual constants. All of the stars except Dubhe and Benatnash are nearly equidistant from us - 74 to 80 light years away - and are part of, indeed the core of, the so-called "Bear Stream," a diffuse cluster of stars moving together in the same direction in space. In addition to a few less bright stars in the same part of the sky - 37, 38, 78, 80 Uma and 21 Leo minor - this stream includes some other stars that are located in completely different places in the celestial vault and have very similar motions through space. These include Sirius of the Big Dog, Gemma of the Northern Crown, δ and ζ Leonis, β Eridani, δ Aquarii, γ Ceti, α Ophiuchi, ι Cephei, β Aurigae. However, since they are separated by several hundred light-years in space, we cannot consider the Bear Stream as an open cluster. Its center is about 75 light-years away, making it our closest physical star cluster, so close that we don't even see it together in the sky. In space, its core occupies an area roughly 32 by 12 light years. But the sun, which is not part of it, lies roughly at its edge. Relative to the Sun, the Bear Stream is moving at about 15 km/s towards a point roughly at the boundary of the constellations Sagittarius and Capricorn.
In the mid-1960s, astronomers analyzing images from the Palomar Sky Survey realized that the sky near the North Celestial Pole was obscured by a little-known dust complex. Some dust clouds were later catalogued by B. T. Lynd and described by Alan Sandage. In the late 1990s, IRAS and DIBHE, two satellites with FIR (far infrared) sensors, collected a wealth of information that finally revealed the full extent of the phenomenon. Detailed maps show that a large amount of dust (covering the constellations of the Big and Little Bear, Cephei, Giraffe and Lynx) stretches from the galactic plane roughly towards the north galactic pole, at a distance of about 300 pc from it. Although the nebulae are very faint in many places, they are not uniform and form dense clouds, bundles, filaments and other recognizable structures that should be given close attention. Like other components of interstellar material, they consist of dust particles, hydrogen, carbon monoxide, and other components.
In addition, these nebulae are unique in that they do not reflect, scatter or shine due to an individual star or star cluster (a feature of most nebulae in the plane of our Galaxy). Properly speaking, we can see these nebulae because they reflect light and are ionized by the total power of all the stars in the Milky Way! They have both reflection (dust scatters blue light) and emission characteristics (ERE - red emission, 600-1000 nanometer band). In short, dark nebulae near the galactic equator are lit up by the Milky Way! It may not be that surprising, but the history of visual observation goes back a long way in this case. In fact, if anyone was seriously interested in this particular field back then, they probably had the opportunity to notice things in the sky that we miss due to light pollution. In 1811, William Herschel compiled a list of 52 areas of the background sky that gave him a hazy impression. Northwest of the galaxy M82, he describes a 1.6-degree area covered in whitish haze. In 2004, an amateur astronomer noticed a faint smudge near galaxies M81-82 in a photo taken with a remotely controlled telescope in the mountains of New Mexico, which is now identified with the Vulcan Nebula, the brightest part of this complex, and probably within the range of an experienced observer.