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STS-118: Highlights

The STS-118 crew, including Barbara Morgan, narrates its mission highlights film and answers questions in this post-flight presentation.

 Full presentation
 Mission film

STS-120: Rollout to pad

Space shuttle Discovery rolls out of the Vehicle Assembly Building and travels to launch pad 39A for its STS-120 mission.


Dawn leaves Earth

NASA's Dawn space probe launches aboard a Delta 2-Heavy rocket from Cape Canaveral to explore two worlds in the asteroid belt.

 Full coverage

Dawn: Launch preview

These briefings preview the launch and science objectives of NASA's Dawn asteroid orbiter.

 Launch | Science

ISS crew change preview

The Expedition 15 mission draws to a close aboard the space station and the Expedition 16 launch nears. These two briefings from Sept. 25 cover the upcoming transition between the two missions.

 Exp. 15 recap
 Exp. 16 preview

Discovery moves to VAB

Shuttle Discovery is transported from its hangar to the Vehicle Assembly Building for attachment to the external tank and boosters.


STS-120: The programs

In advance of shuttle Discovery's STS-120 mission to the station, managers from both programs discuss the flight.


STS-120: The mission

Discovery's trip to the station will install the Harmony module and move the P6 solar wing truss. The flight directors present a detailed overview of STS-120.

 Part 1 | Part 2

STS-120: Spacewalks

Five spacewalks are planned during Discovery's STS-120 assembly mission to the station. Lead spacewalk officer Dina Contella previews the EVAs.

 Full briefing
 EVA 1 summary
 EVA 2 summary
 EVA 3 summary
 EVA 4 summary
 EVA 5 summary

The Discovery crew

The Discovery astronauts, led by commander Pam Melroy, meet the press in the traditional pre-flight news conference.


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Hubble shows 'baby' galaxy is not so young after all
Posted: October 18, 2007

The NASA/ESA Hubble Space Telescope has found out the true nature of a dwarf galaxy that astronomers had for a long time identified as one of the youngest galaxies in the Universe. Astronomers using the NASA/ESA Hubble Space Telescope have made observations of the galaxy I Zwicky 18 which seem to indicate that it is in fact much older and much farther away than previously thought.

Credit: NASA, ESA, and A. Aloisi (European Space Agency and Space Telescope Science Institute)
Download larger image version here

Observations of I Zwicky 18 at the Palomar Observatory around 40 years ago seemed to show that it was one of the youngest galaxies in the nearby Universe. The studies suggested that the galaxy had erupted with star formation billions of years after its galactic neighbours, like our galaxy the Milky Way. Back then it was an important finding for astronomers, since this young galaxy was also nearby and could be studied in great detail; something that is not possible with observations made across great distances when the universe was much younger.

But these new Hubble data have quashed that possibility. The telescope found fainter older red stars contained within the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as 10 billion years ago. The galaxy, therefore, may have formed at the same time as most other galaxies.

"Although the galaxy is not as youthful as was once believed, it is certainly developmentally challenged and unique in the nearby Universe," said astronomer Alessandra Aloisi from the European Space Agency/Space Telescope Science Institute, who led the new study.

Spectroscopic observations with ground-based telescopes have shown that I Zwicky 18 is mostly composed of hydrogen and helium, the main ingredients created in the Big Bang. In other words the stars within it have not created the same amounts of heavier elements as seen in other galaxies nearby. Thus the galaxy's primordial makeup suggests that its rate of star formation has been much lower than that of other galaxies of similar age. The galaxy has been studied with most of NASA's telescopes, including the Spitzer Space Telescope, the Chandra X-ray Observatory, and the Far Ultraviolet Spectroscopic Explorer (FUSE). However, it remains an outstanding mystery why I Zwicky 18 formed so few stars in the past, and why it is forming so many new stars right now.

The new Hubble data also suggest that I Zwicky 18 is 59 million light- years from Earth, almost 10 million light-years more distant than previously believed. On extragalactic standards this is still in our own backyard yet the galaxy's larger-than-expected distance may now explain why astronomers have had difficulty detecting older, fainter stars within the galaxy until now. In fact, the faint old stars in I Zwicky 18 are almost at the limit of Hubble's sensitivity and resolution.

Aloisi and her team discerned the new distance by observing blinking stellar distance-markers within I Zwicky 18. Massive stars, called Cepheid variables, pulse with a regular rhythm. The timing of their pulsations is directly related to their brightness. By comparing their actual brightness with their observed brightness, astronomers can precisely measure their distance. The team determined the observed brightness of three Cepheids and compared it to the actual brightness predicted by theoretical models specifically calculated for the low metal content of I Zwicky 18 in order to determine the galaxy's distance. The Cepheid distance was also validated through another distance indicator, specifically the observed brightness of the brightest red stars in a characteristic stellar evolutionary phase (the so-called "giant" phase).

Cepheid variable stars have been studied for decades (especially by Hubble) and have been instrumental in the determination of the scale of our universe. This is the first time, however, that variable stars with so few heavy elements were found. This may provide unique new insights into the properties of variable stars, which is now a topic of ongoing study.