NGC 2261 (also known as Hubble's Variable Nebula or Caldwell 46) is a

variable nebula Variable nebulae are reflection nebulae that change in brightness because of changes in their star. See also *McNeil's Nebula *NGC 1555 (Hind's Variable Nebula) *NGC 2261 NGC 2261 (also known as Hubble's Variable Nebula or Caldwell 46) is a v ...

located in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Monoceros Monoceros ( Greek: , "unicorn") is a faint constellation on the celestial equator. Its definition is attributed to the 17th-century cartographer Petrus Plancius. It is bordered by Orion to the west, Gemini to the north, Canis Major to the s ...

. The nebula is illuminated by the star R Monocerotis (R Mon), which is not directly visible itself.

Observing history

The first recorded observation of the nebula was by

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

on 26 December 1783, being described as considerably bright and 'fan-shaped'. It had long been designated as H IV 2, after being the second entry of Herschel's class 4 category for nebulae and star clusters, in his catalogues of nebulae. NGC 2261 was imaged as

Palomar Observatory The Palomar Observatory is an astronomical research observatory in the Palomar Mountains of San Diego County, California, United States. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...

Hale Telescope The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in San Diego County, California, US, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation in 1928, he orchestrated the planning, de ...

's first light by

Edwin Hubble Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. He played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology. Hubble proved that many objects previously ...

on January 26, 1949, some 20 years after the Palomar Observatory project began in 1928. Hubble had studied the nebula previously at Yerkes and Mt. Wilson. Hubble had taken photographic plates with the Yerkes 24-inch (60.96 cm) reflecting telescope in 1916. Plates were taken using the same telescope in 1908 by F.C. Jordan, allowing Hubble to use a

blink comparator A blink comparator is a viewing apparatus formerly used by astronomers to find differences between two photographs of the night sky. It permits rapid switching from viewing one photograph to viewing the other, "blinking" back and forth between t ...

to search for any changes over time in the nebula. NGC 2261 was imaged by the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

, and an image of the nebula was released in 1999. A timelapse of NGC 2261 was taken over a period of 6 months by over 20

amateur astronomer Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomers m ...

s at the

Big Amateur Telescope Big or BIG may refer to: * Big, of great size or degree Film and television * ''Big'' (film), a 1988 fantasy-comedy film starring Tom Hanks * ''Big'', a 2023 Taiwanese children's film starring Van Fan and Chie Tanaka * ''Big!'', a Discovery ...

from October 2021 – April 2022. In August 2022, the project was resumed as NGC 2261 came out from behind the Sun. NGC2261 LRGB season 2021-22 18fps

Descriptions

The star R Monocerotis has lit up a nearby cloud of gas and dust, but the shape and brightness slowly changes visibly even in small telescopes over weeks and months, and the nebula looks like a small comet. One explanation proposed for the variability is that dense clouds of dust near R Mon periodically block the illumination from the star. This casts a temporary

shadow A shadow is a dark area on a surface where light from a light source is blocked by an object. In contrast, shade occupies the three-dimensional volume behind an object with light in front of it. The cross-section of a shadow is a two-dimensio ...

on the nearby clouds.

References

External links

European Homepage for the HST
– Hubble photos and information on NGC 2261
wikispaces.com
– Images by amateur astronomers
Astrobiscuit: Seeing The Speed Of Light
fun and educational video about variable nebula and the amateur community observing them * * {{Clear

2261 In contemporary history, the third millennium is the current millennium in the ''Anno Domini'' or Common Era, under the Gregorian calendar. It began on 1 January 2001 ( MMI) and will end on 31 December 3000 ( MMM), spanning the 21st to 30th ...

Monoceros 046b Reflection nebulae Astronomical objects discovered in 1949

• In typography, a bullet or bullet point, , is a typographical symbol or glyph used to introduce items in a list. For example: * Monica * Erica * Rita * Tina * Sandra * Mary * Jessica The bullet symbol may take any of a variety of shapes, s ...