A Slice of Lemon

Credit: Howard Bond (Space Tele­scope Sci­ence Insti­tute), Robin Cia­r­dullo (Penn­syl­va­nia State Uni­ver­sity) and NASA

IC 3568 glows like a lemony plasma globe in this image from NASA’s Hub­ble Space Tele­scope.

Explore the image of the tiny plan­e­tary neb­ula, also called the Lemon Slice Neb­ula. IC 3568 is also one of the sim­plest plan­e­tary neb­u­lae astronomers have observed. Faint struc­ture, like the inside of a lemon, can be seen in the bright cen­tral bub­ble sur­round­ing the cen­tral star. A faint halo extends beyond the bright cen­ter in this clas­sic “round” plan­e­tary nebula.

IC 3568 is a young plan­e­tary neb­ula hav­ing has a diam­e­ter of only about 0.4 light-years or about 800 times the size of our solar sys­tem. This means it would take a beam of light less than a six months to cross the nebula.

Plan­e­tary neb­ula have noth­ing to do with plan­ets except that to early astronomers these round, bub­bles of gas looked like the plan­ets Uranus and Nep­tune. Plan­e­tary neb­ula are the last stage of life for stars like our Sun. After bil­lions of years, stars reach a point where there is lit­tle hydro­gen gas to burn. To help con­vert their stel­lar fur­naces to burn other ele­ments such as helium, the star bal­loons in size to become a red giant. Even­tu­ally, how­ever, the star col­lapses back on itself. This increases the tem­per­a­ture at its core and most of the star’s mate­r­ial is cat­a­pulted into space, form­ing a bub­ble around the star. This doesn’t hap­pen all at once but in stages.

IC 3568 lies about 9,000 light-years from Earth toward the con­stel­la­tion Camelopardalis, the Giraffe. Camelopardalis is the Latin word for giraffe; a camel-like ani­mal, with a long neck and spots of a leop­ard. When first seen, camels amazed crowds through­out the Roman world. Camelopardalis is a faint con­stel­la­tion prob­a­bly cre­ated by Petrus Plan­cius for his star atlas. The Greeks saw no con­stel­la­tions in the part of the sky near the North Star and con­sid­ered it to be empty.