Greetings, stargazers.
Light from distant stars travels for years in a perfectly straight line to get to Earth, only to be jiggled around and dispersed by the atmosphere in the last few kilometers of its path. Throughout most of history, astronomers were limited in their view of the sky by that fuzziness produced by atmospheric turbulence.
That all changed when the Hubble Space Telescope was launched in 1990. Before that time, giant Earth-based telescopes could gather huge amounts of light, yet not resolve significantly more detail than many amateur scopes. The high-resolution images that Hubble produced were astounding, and the scientific output certainly followed suit.
In the years since 1990, computer technology has significantly closed the gap in resolution for ground-based telescopes, so many of them are now limited more by their optics rather than by the atmosphere. But a second reason for launching space-based telescopes is to view wavelengths that are blocked by the atmosphere. No amount of technical improvements will change that limitation.
The James Webb Space Telescope is scheduled to launch later this year to be a successor (not a replacement) of the Hubble Space Telescope. The potential for another giant leap in imaging and science is highly anticipated. The light-gathering area of the Webb is more than six times that of Hubble, which means it should be able to view dimmer objects at a higher resolution than the Hubble.
The instruments on Webb will be looking at mostly infrared light, which has a much harder time passing through the atmosphere than visible light. Because of cosmological expansion, objects that are the most distant from the solar system emit light that has been red-shifted out of the visible and into the infrared.
This means that Webb is even better suited than Hubble to look at the most distant objects in the universe. To enable the infrared instruments to work better, the Webb telescope will deploy a giant sun shield so the telescope can always be in its shadow and stay cooler.
The mirror and sun shield on the Webb are so big that they must be folded to fit into any launch vehicle. Rather than being in low Earth orbit like Hubble, Webb will be positioned much farther from the Earth than the moon in a stable point along the Earth-sun line. Unfortunately, this extreme distance means it cannot be serviced once it is launched.
Venus, the evening star, is prominent in the southwestern sky at dusk, but it will set soon after it gets fully dark. That leaves Jupiter in the southeastern sky as the brightest object. A couple of fist widths to the right of Jupiter is Saturn. Neptune is at opposition on Sept. 14, but you would need a telescope and a detailed star chart to find that tiny point of light.
The summer Milky Way is a glorious sight this month. It passes almost directly overhead in the early evening with bright stars, constellations and clusters along the entire path.
Starting from the southern horizon and looking up, you will find the brightest part of the Milky Way in the direction of the galaxy’s central black hole. Here the teapot asterism of Sagittarius appears to be pouring something on the tail of Scorpius, and the steam coming up from the spout is made of the countless stars of the Milky Way.
Above Sagittarius is Aquilla the eagle, with its short neck and long tail flying north to meet Cygnus the swan, with its long neck and short tail flying south from the zenith. Farther to the north is Cassiopeia and beyond that is Perseus, near the northeast horizon.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. Reach him at hakes_c@fortlewis.edu.
Useful links
JAMES WEBB SPACE TELESCOPE: https://go.nasa.gov/3kZFcIk.
WEBB vs. HUBBLE: https://go.nasa.gov/3DTAcOl.
TRANSPARENCY AND ATMOSPHERIC EXTINCTION: https://bit.ly/3heUBU8.
ASTRONOMY PICTURE OF THE DAY: http://apod.nasa.gov/apod.
OLD FORT LEWIS OBSERVATORY: www.fortlewis.edu/observatory.
AN ASTRONOMER’S FORECAST FOR DURANGO: https://bit.ly/2eXWa64.
FOUR CORNERS STARGAZERS: https://bit.ly/2pKeKKa.
