description Hubble's Variable Nebula (NGC 2261) Overview
Hubble's Variable Nebula, designated NGC 2261, is a fan-shaped reflection nebula located in the constellation Monoceros. It was first recognized for its changing appearance by astronomer Edwin Hubble in 1916, based on photographic plates taken over time. The nebula's variability is caused by shadows cast by dense dust clouds moving near its illuminating star, R Monocerotis, altering its visible structure over periods of weeks or months.
help Hubble's Variable Nebula (NGC 2261) FAQ
What makes NGC 2261 variable?
NGC 2261 is a reflection nebula lit by the young variable star R Monocerotis, or R Mon. Dense dust near the star can block its light and cast moving shadows across the nebula, so its brightness and shape change over weeks. [NASA](https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-caldwell-catalog/caldwell-46/)
Who first studied Hubble's Variable Nebula?
Edwin Hubble published an early study of its changing appearance in 1916, which is why the object carries his name. The nebula itself had been observed earlier, including by William Herschel in 1783. [NASA ADS](https://adsabs.harvard.edu/pdf/1916ApJ....44..190H)
Where is Hubble's Variable Nebula, and how far away is it?
It is in Monoceros and is about 2,500 light-years from Earth. Its fan shape points away from R Monocerotis, which sits at the bright end of the reflection nebula. [NASA](https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-caldwell-catalog/caldwell-46/)
Can an amateur astronomer observe NGC 2261?
Yes, but it is a faint deep-sky target with an apparent magnitude around 10, so a telescope and reasonably dark sky help. Its changing appearance is not a live flicker in minutes; the useful variation occurs over weeks and longer photographic comparisons.
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