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Hubble completes majestic galaxy portrait

spiral galaxy
Spiral galaxy NGC 4414

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June 17, 1999
Web posted at: 4:37 p.m. EDT (2037 GMT)

By Robin Lloyd
CNN Interactive Senior Writer

(CNN) -- NASA this week released a portrait of a majestic spiral galaxy begun by the Hubble Space Telescope four years ago but left incomplete until earlier this year.

Astronomers with the Baltimore-based Space Telescope Science Institute, which analyzes data from the Hubble, revisited the galaxy, called NGC 4414, and completed the image by looking at its other half with the same filters used to "paint" its first half in 1995.

"Originally, the Wide Field Planetary Camera would give you an image which has a cutout in it," said Hubble spokeswoman Cheryl Gundy. "So you have to go back and use the telescope and position it so the camera is in a different orientation so we can get additional data to complete the image."

The new Hubble picture shows that central regions of the galaxy contain primarily older, yellow and red stars, as is typical of most spiral galaxies, Gundy said.

The outer spiral arms show considerably more blue because of the ongoing formation of young, blue stars, the brightest of which can be seen individually at the high resolution provided by the Hubble camera.

The arms also are very rich in clouds of interstellar dust, seen as dark patches and streaks silhouetted against the starlight.

The Hubble Space Telescope originally collected data on NGC 4414 as part of the HST Key Project on the Extragalactic Distance Scale. An international team of astronomers, led by Wendy Freedman of the Observatories of the Carnegie Institution of Washington, observed the galaxy on 13 different occasions over the course of two months.

Images were obtained with Hubble's Wide Field Planetary Camera through three different color filters. Based on their discovery and brightness measurements of variable stars in NGC 4414, the Key Project astronomers were able to make an accurate determination of the distance to the galaxy.

The resulting distance to NGC 4414, 19.1 megaparsecs, or about 60 million light-years, along with similarly determined distances to other nearby galaxies, contributes to astronomers' overall knowledge of the rate of expansion of the universe.

The Hubble constant is the ratio of how fast galaxies are moving away from us to their distance from us. This astronomical value is used to determine distances, sizes, and the intrinsic luminosities, or the brightness, for many objects in our universe, and the age of the universe itself.

Astronomers with the Hubble Heritage Team collected the data to complete the portrait of NGC 4414.

The Heritage Team works to pull information from the Hubble data archives which has not yet been made public, and expand it to make aesthetically pleasing images, Gundy said.

The goal is to create "almost a piece of art, if you will," Gundy said.

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June 1, 1999
Astronomers calculate age of the universe
May 25, 1999
Anxiety high as NASA prepares for Hubble repair job
May 20, 1999
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Hubble Heritage Project- NGC 4414
Space Telescope Science Institute
The Next Generation Space Telescope
Wide Field Planetary Camera
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