The top image appears to be an image made by Rob Gendler with a small telescope from the ground. It is used on many of the Hubble pages about M31, since the HST can only capture a fraction of the entire galaxy. I also think Gendler produced a very large mosaic of M31 out of HST imagery.ErnieM wrote:Here are two pictures, first one from outerspace, the Hubble telescope, the other from the land based Subaru's HPC telescope.
You made a very good point. I may have been fooled by the writing on the picture.I am really and truly surprised that the top picture is supposed to be a Hubble picture.
Wide-field View of the Andromeda Galaxy
Image Type: Observation Object Name: Andromeda Galaxy, Messier 31 Credit: ESA/Hubble & Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble) Tags: Galaxy
Subaru's HPC telescope
Still a mosaic, however, which means we aren't necessarily seeing the true resolution of the system (or we may, depending on whether the original uses the full resolution images).ErnieM wrote:How about this one?
Hah, yeah, when Hubble looks at Andromeda it's like if someone were to try to make a portrait of your face a few skin pores at a time. I am a bit of a Hubble fangirl but I don't think I've ever seen a ground based image that trumps Hubble in terms of clarity. Hubble has that annoying tendency to leave black lines everywhere, though. I am going to sob quietly into my pillow if the JWST somehow gets canceled or crashes. More space telescopes!stephen63 wrote:I did a screen capture of the Hubble images footprint for WFC3 and ACS cameras.
Yay!geckzilla wrote: I am going to sob quietly into my pillow if the JWST somehow gets canceled or crashes. More space telescopes!
Then why are the best telescopic views of Pluto from Hubble?Chris Peterson wrote:
Ground-based telescopes have long outperformed HST in terms of resolution. Where HST has shone is in its ability to achieve relatively high resolution (limited by its rather small mirror) over a much wider field of view than ground-based telescopes.
I'm not sure that the best views are from Hubble. But if they are, there may be good reasons- the near-IR band generally required for adaptive optics may be poorly suited to looking at planets, Pluto might be too bright to effectively use an artificial guide star, and too large to use as a reference itself, observing time for such an object may be more available with the HST than with one of the world's huge ground-based scopes. Suffice to say, those giant scopes operate at much higher resolutions than Hubble is capable of, given the right target.neufer wrote:Then why are the best telescopic views of Pluto from Hubble?Chris Peterson wrote: Ground-based telescopes have long outperformed HST in terms of resolution. Where HST has shone is in its ability to achieve relatively high resolution (limited by its rather small mirror) over a much wider field of view than ground-based telescopes.
Chris Peterson wrote:I'm not sure that the best views are from Hubble. But if they are, there may be good reasons- the near-IR band generally required for adaptive optics may be poorly suited to looking at planets, Pluto might be too bright to effectively use an artificial guide star, and too large to use as a reference itself, observing time for such an object may be more available with the HST than with one of the world's huge ground-based scopes. Suffice to say, those giant scopes operate at much higher resolutions than Hubble is capable of, given the right target.neufer wrote:Then why are the best telescopic views of Pluto from Hubble?Chris Peterson wrote: Ground-based telescopes have long outperformed HST in terms of resolution. Where HST has shone is in its ability to achieve relatively high resolution (limited by its rather small mirror) over a much wider field of view than ground-based telescopes.
http://www.lesia.obspm.fr/perso/bruno-sicardy/predic_occn_12/Pluto_18jul12/index.html wrote: <<On 18 July 2012 around 04:13 UT, a star in the Sagittarius constellation was occulted by the dwarf planet Pluto. The event was attempted from various sites in South America:
It was successfully monitored from various sites in Chile, Argentina and Peru. It was in particular observed at the Cerro Paranal facility of the European Southern Observatory in Chile, with the 8.2-m Very Large Telescope Yepun, using the infrared NACO camera in H band (1.65 μm), in which star was about five times brighter than Pluto.
The event was observed by Julien Girard during a ToO (Target of Opportunity) triggered as part of run ESO 089.C-0314(C)
The proximity of the dwarf planet to zenith at Paranal, photometric conditions and excellent seeing (about 0.5 arcscec in H band) allowed us to record a high signal to noise Pluto occultation event.
http://en.wikipedia.org/wiki/Hubble_Space_Telescope#Impact_on_astronomy wrote: <<The Hubble Space Telescope (HST)'s angular resolution is limited only by diffraction, rather than by the turbulence in the atmosphere. At that time ground-based telescopes were limited to resolutions of 0.5–1.0 arcseconds, compared to a theoretical diffraction-limited resolution of about 0.05 arcsec for a telescope with a mirror 2.5 m in diameter. Even before Hubble was launched, specialized ground-based techniques such as aperture masking interferometry had obtained higher-resolution optical and infrared images than Hubble would achieve, though restricted to targets about 108 times brighter than the faintest targets observed by Hubble. Since then, advances in adaptive optics have extended the high-resolution imaging capabilities of ground-based telescopes to the infrared imaging of faint objects. The usefulness of adaptive optics versus HST observations depends strongly on the particular details of the research questions being asked. In the visible bands, adaptive optics can only correct a relatively small field of view, whereas HST can conduct high-resolution optical imaging over a wide field. Only a small fraction of astronomical objects are accessible to high-resolution ground-based imaging; in contrast Hubble can perform high-resolution observations of any part of the night sky, and on objects that are extremely faint.>>
Like I said, I would be most surprised if Hubble was used to photograph large angular size nearby galaxies like M31 and M33. But I really think that Hubble can take great pictures of galaxies in the Virgo galaxies and a little further away, too. One of my own Hubble favorites is this picture of blue (yes, truly blue!) galaxy NGC 1309, which is about 100 million light-years away.Chris wrote:
Ground-based telescopes have long outperformed HST in terms of resolution. Where HST has shone is in its ability to achieve relatively high resolution (limited by its rather small mirror) over a much wider field of view than ground-based telescopes. In order to compensate for atmospheric distortion, scopes on the ground (which can have very large mirrors, and therefore very high resolution) utilize adaptive optics. This can only work for a tiny area around a reference star or artificial star (created with a laser), and also works best at longer wavelengths (typically near-infrared). But adaptive optics techniques are improving, with more complex wavefront modifiers and the ability to use more reference stars, which has resulted in the correctable fields getting steadily larger.
Mybe Not yet. But very soon.Could a large ground-based telescope take a better picture of NGC 1309? If so, how many individual "pointings" would it require?
If by "better" you mean more aesthetic, almost certainly not. Adaptive optics methods tend to work quite poorly for any sort of color images, since they typically take advantage of the larger correctable patch size you get with longer wavelength imaging. And, as you note, if AO is required to stabilize the seeing, you'd need quite a few images to combine in a mosaic.Ann wrote:Could a large ground-based telescope take a better picture of NGC 1309? If so, how many individual "pointings" would it require?
http://universe.utoronto.ca/press-releases/brite wrote:
tmtWorld’s Smallest Space Telescope<<The smallest astronomical satellite ever built [was launched] on Monday, 25 February 2013 from the Satish Dhawan Space Centre in Sriharikota, India, along with its twin, also designed in Canada, but assembled in Austria.as part of a mission to prove that even a very small telescope can push the boundaries of astronomy. The satellite was designed and assembled at the Space Flight Laboratory (SFL) of the University of Toronto Institute for Aerospace Studies (UTIAS).
Each nano-satellite in the BRIght Target Explorer (BRITE) mission is a cube 20 centimetres per side, and weighing less than 7 kilograms. The BRITE satellites are part of the new wave of nano-satellites that can be designed, assembled and deployed fast and relatively cheaply.
Up to now, such nano-satellites had been used only to monitor the earth and experiment with new technologies. “Researchers, scientists and companies worldwide, who have great ideas for space-borne experiments, but do not have the means to fund a large spacecraft, can now see their ideas realized,” says Grant. “BRITE has the potential to open an entirely new market for low-cost high-performance satellites.”
BRITE is the first nano-satellite mission intended for astronomy, and the first-ever astronomy constellation —more than one satellite working toward a common objective— of any size. The previous world-record holder for small astronomy satellites was the MOST satellite, designed and assembled in part by SFL at UTIAS. Launched in 2003 and still operating, MOST was the first entirely Canadian satellite for astronomy, weighing in at 53 kilograms. Compared to the 11 metric tons of the Hubble Space Telescope, MOST was aptly called a micro-satellite.
“BRITE is expected to demonstrate that nano-satellites are now capable of performance that was once thought impossible for such small spacecraft,” says Grant. But only small telescopes can fit within a 20 centimetre cube. Therefore, BRITE is not intended to take pretty pictures, but will simply observe stars and record changes in their brightness over time. Such changes could be caused by spots on the star, a planet or other star orbiting the star, or by oscillations and reverberations within the star itself —the analogue of earthquakes on stars. The study of these so-called “starquakes” is called asteroseismology.
To perform precise measurements of the brightness of stars, the telescopes need to be above the atmosphere. Otherwise, scintillation —the atmospheric effect that causes stars to twinkle— overwhelms the relatively small brightness variations of the stars themselves. By avoiding this, a very small telescope in space can produce more accurate data than a much larger telescope on the ground. Also, unlike telescopes on Earth which are useless during the day, in bad weather or when the stars set below the horizon, telescopes in space can potentially observe stars all the time.
As their name suggests, the BRITE satellites will focus on the brightest stars in the sky including those that make up prominent constellations like Orion the Hunter. These stars are the same ones visible to the naked eye, even from city centres. Because very large telescopes mostly observe very faint objects, the brightest stars are also some of the most poorly studied stars. It turns out that the brightest stars are also the largest. Big bright stars lead short and violent lives and deaths (supernovas) and in the process seed the universe with heavy elements without which life on Earth would be impossible. To better understand these stars is to better understand how life arose on our planet.
Because big objects oscillate and quake slower than smaller ones, the BRITE satellites do not have to keep their eyes constantly on any given star, but can observe from time to time to see if anything has changed —as children do in the game Mr. Wolf, where they only take a peek at their playmates once in a while, but are still able to tell if any of them has changed position. Hence, the BRITE satellites can monitor their target stars whatever orbit they are placed on, and do not require a dedicated rocket to place them in a specific orbit. By piggy-backing on any available rocket, the BRITE satellites can thus be launched for relatively little money: the first two BRITE satellites will be sent to space on the Polar Satellite Launch Vehicle (PSLV) C20.
To gather more observations and to increase the lifetime of the mission, scientists will be launching three such pairs of satellites —one Austrian pair, one Polish pair and one Canadian pair supported by the Canadian Space Agency— so that within a few years BRITE will become a constellation of six satellites. Each twin in a pair watches the sky in a different colour (red or blue), providing another exciting layer of data to the scientists.>>
"BRITE is not intended to take pretty pictures, but will simply observe stars and record changes in their brightness over time."Beyond wrote:
Well, that certainly is a BRITE idea! When do we get to see pictures?
Well, when do we get to see some ugly ones, then?neufer wrote:BRITE is not intended to take pretty pictures,
Beyond wrote:Well, when do we get to see some ugly ones, then?neufer wrote:
BRITE is not intended to take pretty pictures,
