Other ring nebulae of ring nebulae

Location: 18h51m.7； right ascension; Declination+32 58' (195 equinox); Luminance 9.3, etc.; The apparent diameter is 83× 59; 18 light years away.

The location is about 2/5 near β between β and γ in Lyra, and a star finder of 4 ~ 5 cm 4～5cm 4 times or more is needed for searching, so that a round surface can be roughly presented. Although a binocular of 5 cm and 7 times can be seen, it is only similar to a star image and is not easy to distinguish. 6cm 4 times the mirror can see that there are faint black spots on the circular surface, 8 cm 6 ~ 1 times can be regarded as a circular ring, and 15cm 1～15 times is more clear, and the difference between the two ends of the long axis of the oval ring can be seen. If you use a 2cm mirror, you can still see the central star of magnitude 13 in the ring, and there is also a dark star of magnitude 15.5, which requires a large telescope of more than 6cm.

This nebula is still expanding at a speed of 19km per second. From spectroscopic observation, it is found that this nebula has only a continuous spectrum, and there are neither bright lines nor dark lines (absorption lines), which seems to be a special celestial body lacking hydrogen and helium.

although its apparent diameter is only a little more than 1', it looks very small, and the luminosity is only 9.3, but it has a strong photosensitive effect. With a lens of more than 3mm and Kodak Tri X film, the ring can be photographed after exposure for 3 ~ 5 minutes. Location: Right ascension 19 h 57 m.4; Declination+22 35' (195 equinox); Luminance 7.6, etc.; The apparent diameter is 8 '× 6'; 72 light years away.

It is located in the constellation Fox without bright stars. When looking for it, it can be extended by the connecting line between the γ star in Lyra and the β star in the head of Cygnus at the same distance. There is a 14th star 25' to the north of it, and there are four fifth-class stars 12, 13, 16 and 17 around it in a semicircle around the radius of about 1. 5, or these five stars can be connected into an M-shape, so M27 is located.

Because M27 is the brightest and largest ring nebula of M celestial body (about 1/4 of the diameter of the moon), even a rectangle can be seen with a 5cm 7 times binoculars, the middle of the rectangle is slightly thinner with a 6cm 4 times lens, and it can be distinguished that it is not a rectangle but a circle with an 8cm 4 times lens, and the two sides are arced inward. The 15cm lens can see the uneven shades in the nebula, and the 2cm lens can see the 13 th central star.

It is called "dumb bell nebula" because its shape is like a dumbbell for sports.

The actual diameter of this nebula is about 1-2 light years, and it is still expanding at the rate of .68 per year. According to this rate, it exploded about 3-4, years ago. Although the luminosity of the central star is only 13, its temperature is as high as 85, degrees (absolute temperature). The nebula is approaching us at a speed of 41km per second.

because of its large and bright area, it is also a good object for photography. A standard lens with a diameter of 5mm is exposed with Kodak Tri X for 2 seconds, and a photo with a recognizable position can be taken by fixed photography. A lens with a diameter of 2mm F4 can be exposed with a tracking method for about 1 minutes, and a telescope with a diameter of more than 1cm F5 can be exposed with a direct focus for 1 minutes, and the shape of a dumbbell can be taken. The larger the aperture, the clearer it will be.

There are also M56 globular clusters and M29 and M39 open clusters in the figure, which are not introduced due to the limitation of space, and only marked for reference when searching.