Nebulae

 

Nebulae are divided into various types and sub-types: diffuse, planetary, emission, dark, and reflection nebulae.

 

So-called planetary nebulae have nothing to do with planets; they are named like this because a number of these nebulae somewhat resemble planets when observed through a telescope. A planetary nebula is formed when an evolving star gently sheds a shell of gas. Often, the evolving star may be seen at the centre of the nebula (as with the Helix Nebula in Aquarius and the Ring Nebula in Lyra).

Similar nebulae may be formed after massive stars explode as supernovae, ejecting into space heavy elements formed within them. Such nebulae are known as supernova remnants (the Crab Nebula in Taurus and the Veil Nebula in Cygnus being two examples).

Emission nebulae are regions where stars are often formed (created). In an emission nebula ultraviolet light from stars within the nebula is absorbed and re-emitted at visible wavelengths. Long exposure photographs often show the beautiful colours of the glowing hydrogen gas. The Great Orion Nebula is probably one of the best examples of such nebulae. Note that planetary nebulae may also be considered as types of emission nebulae when they consist of an expanding, glowing shell of ionized gas that has been ejected from red giant stars late in their lives.

The large amount of gas and dust that exists within the Galaxy is commonly concentrated into the dense ‘clouds’ we refer to as nebulae. When thick masses of dust block the light from distant stars forming a conspicuous ‘silhouette’ shape against a brighter background, we end up with so-called dark nebulae. The Horsehead Nebulae in Orion is a fine example.

In a reflection nebula, clouds of dust reflect light from hot, young stars lying in front of them. Gas may also be present but it is only in a few cases that the stars within them provide sufficient energy to make the gas glow. Long exposure photographs of the Pleiades, for example, show these reflection nebulae withing them.

 

Following are a selection of images of nebulae taken over a span of several years.

 

The Dumbbell Nebula (M27) in constellation Vulpecula

Exposure: 8 mins (48 frames of 10s each); gain 250 Equipment: Sky-Watcher 150mm f/5 Newtonian, ZWO ASI385MC, prime focus

Date: 11-Jul-2020 21:30 UTC Location: Santa Venera. © Mario Aloisio

The Dumbbell Nebula is an example of a planetary/emission nebula situated at approximately 1360 light-years. Charles Messier is credited to have first discovered it in 1764. With an apparent visual magnitude of about 7.5 and an angular diameter of about 8 arcminutes, it is easily visible in a small telescope.

A wide-field image of the Dumbbell Nebula (M27) in constellation Vulpecula

Exposure: 1m 20s (8 frames of 10s each), ISO 400 Equipment: Sigma 300mm f/4 APO telephoto lens attached to a Canon EOS 5D Mark II

Date: 20-Oct-2020 19:25 UTC Location: Santa Venera. © Mario Aloisio

The Rosette Nebula in constellation Monoceros

Exposure: 27 minutes (stack of 41 frames) Equipment: Vivitar 200mm f/3.5 lens set at f/5.6 and attached to a ZWO ASI585MC camera

Date: 6-Feb-2024 20:14 UTC Location: Santa Venera. © Mario Aloisio

The Rosette Nebulae (NGC 2237) is a massive, star-forming region, a glowing red cloud of hydrogen gas about 100 light-years in diameter. At the centre of this nebula is a star cluster (NGC 2244 or Caldwell 50), easily identifiable through binoculars. The distance of the Rosette Nebula is about 5200 light-years. Angular diameter is about 1.3 degrees, and visual magnitude about 9. The Rosette Nebula is an example of an emission nebula (H II—ionized hydrogen— region).

The Great Orion Nebula (M42)

Exposure: 2m 10s (stack of 7 frames), ISO 800 Equipment: Celestron 203mm f/5 Newtonian, Canon EOS Kiss x7i (700D)

Date: 26-Jan-2022 18:41 UTC Location: Santa Venera. © Mario Aloisio

The Orion Nebula is one of the brightest in the sky, easily visible with the naked eye from dark sites. It is a place where stars and planetary systems are being formed. It is an example of a diffuse/reflection/emission nebula. Distance: ca. 1340 light-years.

The Great Orion Nebula (M42)

Exposure: 14 minutes (stack of 37 frames) Equipment: Tamron AF70-300mm f/4-5.6 with lens set at 135mm and attached to ZWO ASI385MC

Date: 9-Feb-2022 21:32 UTC (Note: The moon was at first quarter.) Location: Santa Venera. © Mario Aloisio

 

This is an image taken with an astro-camera attached to a telephoto lens.

The Flame and Horsehead Nebulae in constellation Orion

Exposure: 18 minutes (stack of 28 frames) Equipment: Vivitar 200mm f/3.5 lens set at f/5.6 and attached to a ZWO ASI585MC camera

Date: 6-Feb-2024 18:01 UTC Location: Santa Venera. © Mario Aloisio

The Horsehead Nebula in constellation Orion

This is a closer view through a telescope.

Exposure: approx. 16 mins (47 frames); gain 250 Equipment: Sky-Watcher 150mm f/5 Newtonian, ZWO ASI385MC, prime focus

Date: 22-Feb-2023 18:40 UTC Location: Santa Venera. © Mario Aloisio