Helix Nebula

Here’s another beautiful Helix Nebula image, this one by Julian Goddy ’21.

Helix Nebula, by Julian Goddy ’21

Julian explains, “The Helix nebula (NGC 7293) is a planetary nebula 650 light years away and 4 light years across in the constellation Aquarius. It is the closest example we have of the planetary nebula from a sun-like star. Planetary nebulae got their name because they looked round like planets when they were first imaged with a small telescope. However, planetary nebulae are not actually planets, but rather the remnants of stars after they have run out of fuel. When this happens, the outer gaseous layers end up getting blown into space, leaving behind a dense hot core called a white dwarf. The hot glow from the white dwarf heats up the expelled gas and causes it to shine. This shining gas is what we see as a planetary nebula such as the Helix. In around 10,000 years, the Helix will no longer be visible because the gas will drift away from the white dwarf and contribute to the recycling of atoms in space.

Due to the dimness of distant objects in space, astronomical images are usually taken in a series of filters that are all greyscale to increase their sensitivity. These filters each detect a particular element in the object. Together, they give a more complete image of its structure. Multiple images are taken in each filter and then aligned and stacked on each other to increase the signal to noise ratio. The images from these filters are then each assigned a different color and then aligned and superimposed on each other to create the final image. In this composite three-color RGB image, Ha is red, doubly ionized oxygen [OIII] is green and singly ionized sulfur [SII)] is blue. Eleven images with 120 second exposures were taken for each filter with the Proline PL 16803 CCD on the 16” telescope at Haverford College’s Strawbridge Observatory. These images were then aligned and stacked together using AstroImageJ. The image was taken on September 19, 2020.”

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