NGC 752, also known as Caldwell 28, is an open star cluster located in the northern constellation of Andromeda. Open clusters consist of stars that formed together from a common molecular cloud, remaining loosely bound by gravity over time. Typically, open clusters contain a few dozen to several thousand stars, offering a unique look at stellar evolution within a relatively small area of space. The distance to NGC 752 from Earth is estimated to be around 1,300 light-years.
Key Features
When observed from Earth, NGC 752 presents a visually rich group of stars that varies in size and brightness. The cluster, with an apparent magnitude of about 5.7, is visible to the naked eye under dark skies. Its angular size of around 50 arcminutes makes it appear relatively large and prominent through binoculars or telescopes. NGC 752 contains stars primarily in later stages of evolution, with ages estimated at around 1.6 to 2 billion years, making it relatively old for an open cluster. Many of its stars are evolving away from the main sequence and transitioning to the giant phase, giving the cluster a distinctive population of red and orange giants.
The cluster’s stars exhibit a range of compositions typical for open clusters of its age, with metallicities similar to those found in our galaxy’s thin disk. This makes NGC 752 useful for studying the chemical composition of stars formed in a similar galactic environment. The mix of red giants and main-sequence stars provides valuable insights into stellar aging and evolutionary processes, particularly as the stars age and begin to expand and cool.
Observation
For observers in the Northern Hemisphere, NGC 752 is ideally viewed from September through February. During this period, the constellation Andromeda rises earlier in the evening and remains visible for extended periods, particularly during autumn. Around November, Andromeda reaches its highest point in the sky in the late evening, offering an optimal viewing window.
With binoculars or a small telescope, NGC 752 reveals individual stars, which enhances its visual appeal as a dense and sparkling patch against the night sky. Higher magnifications allow observers to resolve its brightest stars, enhancing its impression as a spacious yet cohesive cluster.
