Heart Nebula

{{short description|Emission nebula in the constellation Cassiopeia}}

{{Infobox nebula

| name = Heart Nebula

| image = Heart Nebula (2020-08-11).jpg

| caption = Heart Nebula, with the Fish Head Nebula on the top right corner, narrowband image captured on a 70 mm scope

| type = H II region

| epoch = J2000.0

| ra = {{RA|02|33|22}}

| dec = {{DEC|+61|26|36}}

| dist_ly = 7500

| appmag_v = 18.3

| size_v = 150' x 150'

| constellation = Cassiopeia

| radius_ly = 165

| absmag_v = 6.5

| notes =

| names = NGC 896, IC1805, Sh 2-190

}}

The Heart Nebula (also known as the Running Dog Nebula, Sharpless 2-190) is an emission nebula, {{convert|7500|ly|pc|lk=on}} away from Earth and located in the Perseus Arm of the Galaxy in the constellation Cassiopeia. It was discovered by William Herschel on 3 November 1787.{{Cite web|url=http://cseligman.com/text/atlas/ngc8a.htm#896|title=New General Catalog Objects: NGC 850 - 899|website=cseligman.com|language=en-US|access-date=2017-12-19}} It displays glowing ionized hydrogen gas and darker dust lanes.{{Cite web|url=http://www.astronomy-mall.com/Adventures.In.Deep.Space/NGC%201-7840%20complete.htm|title=astronomy-mall.com/Adventures.In.Deep.Space/NGC%201-7840%20complete.htm|website=astronomy-mall}}

The brightest part of the nebula (a knot at its western edge) is separately classified as NGC 896, because it was the first part of the nebula to be discovered. The nebula's intense red output and its morphology are driven by the radiation emanating from a small group of hot stars near the nebula's center. This open cluster of stars, known as Collinder 26, Melotte 15, or IC 1805, contains a few bright stars nearly 50 times the mass of the Sun, and many more dim stars that are only a fraction of the Solar mass.

The Heart Nebula is also made up of ionised oxygen and sulfur gasses, which are responsible for the rich blue and orange colours seen in narrowband images. The nebula also spans almost 2 degrees in the sky, covering an area four times that of the diameter of the full moon.{{Cite web|title=The Heart Nebula in Hydrogen, Oxygen, and Sulfur {{!}} Science Mission Directorate|url=https://science.nasa.gov/heart-nebula-hydrogen-oxygen-and-sulfur|access-date=2021-12-30|website=science.nasa.gov|archive-date=2021-12-30|archive-url=https://web.archive.org/web/20211230115916/https://science.nasa.gov/heart-nebula-hydrogen-oxygen-and-sulfur|url-status=dead}}