DEEP-SKY TOUR
We explore the celestial highlights found in eastern Cassiopeia
1 M103
This month’s ‘Deep-Sky Tour’ takes us through some of the wonders found in eastern Cassiopeia, a rich part of the sky thanks to the background presence of the
Milky Way. M103 is an open cluster located a degree east-northeast of Ruchbah (Delta (d) Cassiopeiae). At mag. +7.4 this is an easy find with any size instrument, but may look a bit underwhelming. The reason for this is that M103 is a sparse open cluster, 6 arcminutes in size, arranged with a triangular shape among a rich star background. Three brighter stars dominate the scene, the one in the middle looking orange compared to the two blue stars either side. The northern most star is a double named Struve 131. SEEN IT.
2 Trumpler 1
Open cluster Trumpler 1 is located 41 arcminutes north-northeast of M103. It’s approximately 4 arcminutes in size and, at mag. +8.1, is bright enough for viewing with any instrument. Visually it appears to contain around 30 members. Four of these, around the 12th magnitude mark, are arranged in a 1.5 arcminute line, which gives Trumpler 1 a distinctive appearance. SEEN IT.
3 NGC 659
Centre up on M103 and drift 1.3˚ to the east to locate mag. +7.9 open cluster NGC 659. Alternatively, locate the mag. +5.8 star 44 Cassiopeiae and NGC 659 is located 11 arcminutes to its northeast. Despite its magnitude rating, NGC 659 is faint through most instruments. A 100mm scope at low power shows a 3 arcminute glow near to 44 Cassiopeiae, while a 250mm scope using a low power eyepiece shows it as a concentration around 3 arcminutes across, containing stars mostly around 11th to 12th magnitude. Higher power eyepieces will make the central region easier to see with larger instruments. SEEN IT.
4 NGC 663
NGC 663 is a star-rich open cluster with a rated magnitude of +7.1. It’s a young cluster, estimated to be younger than 25 million years old, and contains an estimated 400 members. It sits 0.6˚ north-northeast of NGC 659 and appears a quarter of a degree across through a 150mm scope, an aperture size which reveals around 30 of the cluster’s 400 members. A 250mm instrument will show twice that number, the cluster’s outer boundary also appearing larger at 20 arcminutes. One odd characteristic of its appearance is the presence of a number of similar brightness star pairs. NGC 663 contains at least five stars known as ‘blue stragglers’; formed when two stars merge together. SEEN IT.
5 NGC 654
Located 40 arcminutes to the northnorthwest of NGC 663 lies our next target, another open cluster called NGC 654. Marginally brighter and larger than NGC 659, at mag. +6.5, it has a full apparent size of 8 arcminutes. Small instruments will see the cluster as a smaller object around the 3-4 arcminute range. The age range of NGC 654 is between 15-40 million years. A 250mm instrument will show NGC 654 to be approximately circular with around 20 stars visible in a 3 arcminute region. A 300mm scope improves on these statistics, expanding the member count by 50 per cent to around 30 stars in an area a bit under 5 arcminutes across. The brightest member is a yellow supergiant star shining at mag. +7.3. SEEN IT.
6 IC 1747
Our final target for this month’s tour isn’t an open cluster: IC 1747 is a 12th magnitude planetary nebula which requires larger apertures to see well. It’s pretty easy to find, being located half-a-degree to the southeast of Segin (Epsilon (e) Cassiopeiae), the star that marks the eastern end of the W-shaped constellation of Cassiopeia. The nebula is characteristic for a planetary in that it appears small at 13 arcseconds across. In its favour, it does appear quite concentrated and should be fairly evident as a planetary nebula for apertures over 250mm at magnifications of 200x or higher. An interesting line of 11th and 12th magnitude stars appears to point towards IC 1747, starting north-northeast of the object. SEEN IT.