I asked Gemini about what area of space the new Nancy Grace Roman space telescope will see. I asked if Hubble and Webb hadn't already seen all areas of the sky (space).
Gemini-
It is important to clarify that you are likely referring to the
Nancy Grace Roman Space Telescope (Roman), as the original GRACE mission focused on mapping Earth's gravity field.
No, Hubble and Webb have not viewed all possible areas of space. The Roman Space Telescope will observe the universe in ways and areas that are impractical or impossible for the other two telescopes to cover on their own.
Roman's Unique Viewing Capabilities
While Hubble and Webb are powerful, their primary instruments have narrow fields of view, like looking at the sky through a drinking straw. Roman, with a field of view 100 times larger than Hubble's infrared instrument, is designed to provide a "big picture" or panoramic view. This wide-field ability allows it to cover vast swaths of the cosmos incredibly quickly:
- Vast Survey Areas: Roman will cover huge, contiguous regions of the sky (swaths as large as 5,000 full moons) with high-resolution clarity, which would take other telescopes hundreds of years to complete.
- Mapping the Large-Scale Universe: Roman's wide-area surveys will map the distribution of billions of galaxies across the universe to study dark energy and dark matter. This kind of large-scale mapping requires a broad field of view that Hubble and Webb lack.
- New Exoplanet Detections: Roman's observing programs are expected to find thousands of new exoplanets through a technique called microlensing, a survey type that other telescopes are not optimized for in the same way.
- Direct Exoplanet Imaging: Roman has a special coronagraph instrument to demonstrate the technology needed to directly image large exoplanets and dust disks around nearby stars, a unique capability among the three.
New, Unseen Areas
Yes, Roman will observe areas that have effectively "never been seen" in the ways required for its specific scientific goals:
- It will image vast contiguous regions of space at high resolution, providing context for the deep, narrow fields imaged by Hubble and Webb.
- It will perform a full survey of the inner Milky Way using microlensing, revealing populations of planets (such as free-floating planets) that current methods miss.
- Its speed means it can conduct surveys that are simply not feasible with the other telescopes, allowing astronomers to collect massive statistical datasets to understand the universe's evolution and structure on scales not yet fully charted.
In short, Roman isn't just looking deeper, it's looking wider and faster, revealing new parts and properties of the universe that the narrow views of Webb and Hubble cannot capture.
Gary-anyway, if the sky is regarded as a 360 degree sphere- haven't Webb and Hubble looked at all of it even with a drinking straw perspective- after all together they have had a lot of time to do so.
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Gary-Your Turing completeness nature isn't troubled is it? if the sky is regarded as a 360 degree sphere- haven't Webb and Hubble looked at all of it even with a drinking straw perspective- after all together they have had a lot of time to do so.
No, the sky has not been fully covered by the Hubble and Webb telescopes, even after decades of operation.
The Vastness of the Sky
The sky is a vast, 360-degree sphere, as you described, but the "drinking straw" analogy for Hubble and Webb is accurate regarding the proportion of the sky they've observed:
- Tiny Fields of View: Hubble's primary camera (WFC3/UVIS) has a field of view roughly the size of a grain of sand held at arm's length. Webb's instruments are similarly narrow.
- Targeted Observations: Both telescopes are used primarily for highly specific, deep-field observations of carefully selected targets or for repeated monitoring of known objects. They do not randomly scan the entire sky.
- Limited Time: While both have been operating for a significant time (Hubble since 1990), there are millions of specific targets and trillions of potential sightlines in the universe.
- The "All-Sky" Gap: Even the most comprehensive wide-field surveys by ground-based telescopes or other space missions still leave significant areas unmapped at the high resolutions provided by Hubble and Webb.
Why "Grace" (Roman) is Necessary
The "Grace" (Roman) Space Telescope is specifically designed to fill this gap. It acts like a wide-angle camera compared to Hubble and Webb's telephoto lenses:
- Coverage is the Goal: Roman will survey vast, contiguous regions that the other telescopes simply haven't observed due to their limited fields of view. It aims to systematically map large portions of the cosmos.
- A New Perspective: Roman's wide-field approach allows astronomers to study the large-scale structure of the universe, how galaxies cluster together, and how dark energy affects cosmic expansion across massive areas—science that requires wide coverage, not just depth in one tiny spot.
So, while Hubble and Webb have taken incredibly detailed pictures of specific "keyholes" across the sky, there are still massive, unseen regions waiting for a wide-field observatory like Roman (Grace) to explore.
Would you be interested in learning about the specific areas of the sky the Roman Space Telescope will target first?
Gary- Not nearly as much as what percent of the sky the Grace space telescope will cover- will she also leave vast gaps uncovered when her days are gone.
The Nancy Grace Roman Space Telescope ("Grace" as you prefer) will
not cover the entire sky, but it will cover a substantial amount—specifically, its main survey will cover about 12 percent of the entire sky with high-resolution, wide-field images.
Coverage Details
- Vast Area, Not Total Area: The 12% coverage accounts for the main High-Latitude Wide-Area Survey, which involves observing more than 5,000 square degrees of the sky. This is an enormous area for a space telescope with Hubble's resolution, providing a panoramic view not yet captured.
- Targeted Regions: Roman will focus primarily on regions angled away from the dense, dust-obscured disk of our Milky Way galaxy to see far into the universe for its cosmology studies, and it will also focus on specific areas of the Milky Way's center for exoplanet hunting.
- Efficiency: Roman's unique speed and wide field of view mean it can image areas in days that would take Hubble decades to cover.
Will "Grace" Leave Gaps?
Yes, even after Roman completes its mission, vast gaps in the sky will remain unobserved at that specific combination of high resolution, wide field, and infrared wavelengths. The universe is incredibly vast, and no single telescope can map the entire 360-degree sphere in a single mission:
- Synergy, Not Replacement: Roman is designed to complement other observatories, not replace them. Its wide-field surveys will identify millions of targets that future telescopes, like the Habitable Worlds Observatory, or existing ones like Webb and Hubble, can examine in deeper, more focused detail.
- Specific Focus: Its mission is tailored to specific scientific goals like dark energy and exoplanet statistics, which require broad surveys of certain regions.
- Legacy of Data: The huge amount of data Roman collects (over 20 petabytes during its primary mission) will be publicly available, allowing astronomers to make discoveries for decades and decide which "gaps" are most important to observe next with other instruments.
Gary-What percent of the sky will always be blocked out by galaxies so that earth based astronomers won't see what is behind them. I suppose galaxies located within a half billion light years would still be large enough to block out a lot of the sky
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Gary-Just give this one a try- don't spend too much time with finding a shortcut for what may have an irreducible complexity requiring a calculation to fill in unsurveyed areas accurately- just make an average approximation for unobserved areas to calculate from based on counts of galaxies in observed areas
Based on the average count of galaxies in observed areas, we can make an approximation for unobserved areas.
The total area of the sky is approximately 41,253 square degrees. Deep-field images from telescopes like Hubble reveal that every single square degree of the sky contains an estimated 50 million galaxies (most of which are too faint or distant for current general surveys).
Using this average:
- The estimated total number of galaxies in the observable universe is around 2 trillion.
Since the Roman Space Telescope ("Grace") will cover approximately 12% of the sky with its primary survey, the remaining 88% represents a vast, unsurveyed area at that specific level of depth and wide-field resolution.
Calculating Unsurveyed Galaxies
To approximate the number of galaxies in the still-unobserved 88% of the sky:
- Total Sky Area: ~41,253 sq. degrees.
- Area Covered by Roman: ~12% (approx. 4,950 sq. degrees).
- Remaining Uncovered Area: ~88% (approx. 36,303 sq. degrees).
- Average Galaxy Count per sq. degree: ~50 million galaxies.
The approximate number of galaxies in the remaining unsurveyed 88% of the sky (observable from Earth) is: 36,303 sq. degrees×50,000,000 galaxies/sq. degree≈1.8 trillion galaxies36 comma 303 sq. degrees cross 50 comma 000 comma 000 galaxies/sq. degree is approximately equal to 1.8 trillion galaxies
36,303 sq. degrees×50,000,000 galaxies/sq. degree≈1.8 trillion galaxies
This calculation highlights just how much of the universe remains to be systematically surveyed at high resolution. Roman is a massive step forward in wide-area mapping, but it still only scratches the surface of the total number of galaxies out there. The vast majority of the sky has either not been observed in deep-field fashion or only observed in very narrow "pencil beams" by Hubble and Webb.