This month, I have only my own observations to report! On 21st July I imaged globular clusters M22 in Sagittarius and NGC6712 in Scutum.
M22 is one of the closest globular clusters to Earth at a distance of about 10,000 light years and is about 70 light years across. NGC 6712 is over twice as far away at 22,500 light years. These images were taken with a Meade LX200 305mm ACF telescope working at f6.3, and a DSI II pro mono camera plus an IR filter.
On the same evening, I imaged NGC 6818, the “little gem” planetary nebula in Sagittarius, same telescope and camera as above but at f10, combining images taken through red green and blue filters with an IR filtered image to make a final LRGB image.
NGC 6818 is magnitude 9.9 with a high surface brightness, and is 48 arcseconds in diameter.
On 25th July I imaged the two bright globular clusters in Hercules, M13 and M92.
Well – known M13 is 140 light years across and 21,000 light years from Earth, whereas M92 is both smaller and more distant, at 80 light years and 25,000 light years. M92 is considered to be one of our Galaxy’s oldest globulars – it’s stars have a very low metallicity.
Also on 25th July I took a further two images; both in the constellation of Lyra. The ring nebula, M57, is a planetary nebula often imaged by amateur astronomers, and this was taken at f10 with same procedure employed on NGC 6818 above. M56, a globular cluster, was also taken at f10. but luminance frames only.
M57 is 1.5 x 1.0 arcminutes across, and the central white dwarf star is magnitude 15.3. This planetary nebula is 2,300 light years away, and is thought to be about 6,000 years old. Its measured expansion rate is 1 arcsecond per 100 years. The blue green tinge caused by doubly ionised oxygen responds well to an OIII filter.
At about 33,000 light years from earth, 84 light years across and magnitude 8.3, M56 is visually less impressive than either M13 or M92.