Objects of the Cosmos

The universe is a vast and immense place which is full of unusual and exotic objects.

My hobby is to observe, record and photograph these objects; but what exactly are they?

A galaxy is a massive gravitationally bound system of stars, planets, nebulous gas, dust and dark matter. Galaxies can vary drastically in size from small dwarfs with 10,000,000 (ten million) stars to absolute giants consisting of 1,000,000,000,000 (one trillion) stars. The entire mass of a galaxy orbits a common centre of mass now known to be a black hole.

A Planetary Nebula is formed by a star that weighs a few times more than our own sun expending its remaining gases and material (mainly Helium) at the end of its life. These objects are very dim and none are visible without the aid of a telescope. Planetary Nebula are only a short-lived phenomenon lasting only a few tens of thousands of years. There are about 1,500 known to exist in our own Milky Way.

A Supernova Remnant is the left over structure from the enormous explosion of a star. This remnant is bound by an expanding shockwave which consists of ejected debris and material from the explosion as well as material collected and swept up by the resulting shockwave turbulent winds.

Diffuse Nebula are areas of interstellar gas clouds that emit visible light. There are two types Emission Nebula which are self luminous and Reflection Nebula which are illuminated by radiation from nearby stars.

B33 - Horsehead Nebula M42 - Orion Nebula NGC 1973 - Running Man Nebula NGC 6888 - Crescent Nebula

A Globular Cluster is a spherical, tightly bound mass of stars that orbit a galactic core. These tend to be located in the halo of a galaxy and are reasonably common, our own Milky Way contains around 150 of them. Globular Clusters can differ in size with a small one containing around 20,000 solar masses while a giant will consist of around several million solar masses. Globular Clusters are reasonably bright and some can just about be seen by the naked eye on a clear night.

An Open Cluster is a group of up to a few thousand stars that are loosely gravitationally bound together. Open Clusters are only found in Spiral and Irregular Galaxies within the disk where active star formations are forming. Open Clusters tend to be quite young stellar objects, only a few hundred million years old. Some Open Clusters are reasonably bright and can be seen by the naked eye on clear nights.

A Star is a massive luminous ball(s) (singular, binary or more) of plasma that group together under the force of gravity to form galaxies which dominate our visible universe. A star is very bright and shines because of nuclear fusion taking place within its core releasing energy that radiates into outer space.

Class	Temperature	Stellar color	Apparent color	Mass	Radius	Luminosity	Hydrogen lines	% of all MSSs
O	30,000–60,000 K	blue	bluish	60	15	1,400,000	Weak	~0.00003125%
B	10,000–30,000 K	blue	bluish	18	7	20,000	Medium	0.13%
A	7,500–10,000 K	blue-white	bluish	3.1	2.1	80	Strong	0.63%
F	6,000–7,500 K	white	bluish	1.7	1.3	6	Medium	3.1%
G	5,000–6,000 K	yellow-white	white	1.1	1.1	1.2	Weak	8%
K	3,500–5,000 K	orange	reddish	0.8	0.9	0.4	Very weak	13%
M	2,000–3,500 K	red	reddish	0.3	0.4	0.04	Very weak	>78%

A Planet is a celestial body orbiting a star that is massive enough to be rounded by its own gravity but not massive enough to cause thermonuclear fusion at its core. Planets can be categorised into four types :-

Planets largely made up of gaseous material that are significantly more massive than terrestrials (Jupiter, Saturn).

Planets distinguished from gas giants by their depletion of hydrogen & helium and a significant composition of rock and ice (Uranus, Neptune).

Planets that are mainly composed of ice and do not have planetary mass (Pluto & Eris).

A Comet is a large chunk of rock, dust and ice that orbits the Sun in our Solar System. A Comet will exhibit visible coma and/or tail that is the effect of solar radiation upon the comets nucleus. Comets originate from the outer Solar System and are thrown inwards by the gravitational effect from planets or by colliding with other cosmic objects.