M103 - Open Cluster in Cassiopeia

Polish version is here

Messier 103 (M103), also designated NGC 581, is an open star cluster located in the constellation Cassiopeia. Situated approximately 8,000 to 9,500 light-years from Earth, it is among the most distant clusters listed in Messier’s catalog. Although it may not be the most visually impressive observation target, M103 stands out due to its relatively early stage of stellar evolution.

The cluster is estimated to be around 25 million years old, placing it among the youngest known examples of its kind. Its stellar population is dominated by hot, blue B-type stars, along with several more evolved objects, including a red supergiant with an apparent magnitude of approximately 10^m, located near the core. These features point to a shared origin, suggesting that the stars formed relatively recently from a single molecular cloud composed of gas and dust.

Observations

September 05, 2024, about 10:30 p.m. - Jaworzno, Poland

urban conditions, high level of light pollution

The star cluster featured here lies about 1° northeast of Ruchbah, also known as Delta Cassiopeiae (δ Cas). Its apparent magnitude of 7.4^m makes it relatively easy to spot, even with a basic pair of binoculars.

Photo 1 – without labels

Photo 1 – with labels

One of the most distinctive aspects of Messier 103 is its triangular appearance. It is composed of roughly 170 stars that are likely gravitationally bound. The system stretches across about 15 light-years and is still partially enveloped in remnants of interstellar dust, which can influence the apparent brightness and color of its individual stars.

Thanks to spectroscopic and photometric observations, combined with data from the Gaia mission, astronomers have determined the proper motions and radial velocities of stars in Messier 103. These findings confirm that the stars originated from the same region of space. Although M103 has not yet begun to break apart, it will eventually disperse over time, as is typical for open clusters, primarily due to the tidal forces exerted by the Milky Way.

While Messier 103 may seem unremarkable compared to more visually stunning clusters, it offers valuable insight into early stellar evolution and the internal dynamics of young stellar systems. For amateur astronomers, it also presents a rewarding target, particularly on clear autumn nights when Cassiopeia climbs high in the northern sky.

September 10, 2025, about 10:00 p.m. - Katowice, Poland

urban conditions, very high level of light pollution

This time I was able to capture a view of the wider surroundings of the M103 cluster, which appear truly striking (Photo 2).

Photo 2 – without labels

Photo 2 – with labels

To the right of M103, slightly below it, the previously mentioned star Ruchbah can be seen. Also clearly visible is the open cluster NGC 659, which is not included in the Messier catalog. The object was most likely discovered by Caroline Herschel (the sister of William Herschel) on September 27, 1783. This star cluster lies at a distance of about 6,300 light-years from the Sun.

A bright, bluish star designated 44 Cas lies near NGC 659. It is a variable star of the Delta Scuti type.

Photo 1 Parameters:

ZWO Seestar s50
Total exposure time: 10 minutes (stack of 60 RAW frames at 10s each)
A filter was used to reduce the effects of artificial light pollution and atmospheric glow

Photo 2 Parameters:

Total exposure time: 30 minutes (stack of 30 RAW frames at 60s each, using an appropriate number of dark, bias, and flat frames)
ISO: 1600
Maksutov-Cassegrain telescope (100/1400), prime focus exposure
A filter was used to reduce the effects of artificial light pollution and atmospheric glow
Mount: equatorial mount with tracking, aligned using the drift method and controlled by a custom-built system.

Weird Science

M103 - Open Cluster in Cassiopeia

Obse­rva­tions

Observations