63

It's a problem because there are still lots and lots and lots of ground-based telescopes. Ground-based telescopes are still (by far) the biggest optical telescopes, and the cost of space telescopes is prohibitive for many research projects. It will be a long time before a telescope anywhere close in size to the VLT can be launched. Most space telescopes are ...


35

Satellites are moving. They are in orbit around the Earth. Satellites in low Earth orbit are moving at about 7000 m/s relative to the ground. You can work out the orbital speed by $$v=\sqrt{\frac{GM}{r}}$$ where $G = 6.673 × 10^{-11}$ and $M=5.97×10^{24}$ and $r$ is the distance from the Earth's centre = altitude + 6370000 metres. (These values are in SI ...


29

Can you explain me in simple words why the satellite in this telescope image appears as a streak? The exposure time is 1 second. This drawing should explain it: (Note: It could be the other way around, too. There's no way to tell from the image which way the satellite was moving.)


21

Large masses can bend light, but space is largely empty. The light from distant stars and galaxies rarely passes close enough to another star or galaxy to have deviated. On the few occasions when it does, it is special and notable. For example, the Einstein cross looks like four quasars in a (very small) square, with a galaxy in front of it. In fact it is ...


15

To expand on the "space telescopes are expensive" aspect: Space telescopes cannot be maintained or repaired. This applies not just to things like optics and instruments, but also to space-specific equipment like gyroscopes and thrusters (the James Webb Space Telescope has an estimated lifetime of $\sim 10$ years, set by the supply of fuel for the ...


14

All "big" instruments have observation logs, so does Spitzer. The complete logs are here but there's also a filtered log for solar system observations which shows basically all planets and especially many minor planets. That said, it's not a general sky survey telescope due to its FOV of 5' x 5', so it's not meant to discover objects in ...


10

There are approved proposals for Cycle 1 to point the JWST at The Jovian system Jupiter's great red spot Mars Saturn and its moons and rings In those PDFs, they describe exactly what instruments they want to point where, but to summarize as far as I can tell they're planning to try to use pretty much all of the available instruments to image Jupiter and ...


8

In addition to the target list linked to by @planetmaker in their answer, there are two recently published review articles (from Nature Astronomy) summarizing the many different aspects of Solar System science that were done with Spitzer: Lisse et al. (2020), "Spitzer's Solar System studies of comets, centaurs and Kuiper belt objects" Trilling et ...


7

More than 20 if the Wikipedia's List of Space Telescopes is accurate. I extracted the active ones, and removed duplicates (to the best of my knowledge): Swift Gamma Ray Burst Explorer AGILE FGST IKAROS NuSTAR Astrosat Insight (Chinese: 慧眼) Спектр-РГ (Spektr-RG) The famous Hubble Space Telescope, HST, see hst STSat-1 IRIS Hisaki Lunar-based ultraviolet ...


7

One thing I always like to add is that ground based telescopes benefit from being able to take huge amounts of data. The Vera Rubin Observatory will have a 3.5 Gigapixel camera. There are proposals to sometimes run it in a mode with 1 second exposures. So we're talking data rates of gigabytes per second. If you have dedicated fiber lines you can deal with ...


7

No For a telescope to be useful, the particles/waves that the telescope detects must reach the telescope. This is why space is a great place to put a telescope: there is nothing, not even air, to block the particles/waves. Light does not penetrate beyond a few mm into the ground, so a telescope in a mine will not get any light from the stars. Bluntly, it ...


7

A relatively simply way to remove the streak is to take two-or-more photos, with a short pause between them. The stars won't move much in that time, but the satellite will have drawn a short dash on each frame. Example, 1s shutter open, 1s pause, 1s shutter open for second frame, etc. Then use image processing to remove pixels that aren't in both/all images....


7

All modes can be used. But for bright targets, observations are limited to specific filters, subarrays, regions of the target planet, or spectral intervals. James Norwood and colleagues wrote a paper on this topic, although the full answer is complicated because of the "subset of the instrument modes" part. The simplest answer to understand is for ...


6

Straight line, though it wont make much difference, The point about the size is that it tells you about how much light the telescope can gather. This is the "projected-flat" area, not the curved surface area. However, the difference is not much, as telescope mirrors are not highly curved. I suppose it makes more of a difference when considering ...


6

Space telescope Astronomy research published in Science and Nature: Ground-based telescopes (31.1%), spacecrafts (27.0%), space telescopes (22.8%). (ref) Number of professional telescopes affected: >1050. (ref) representing tens of thousands of academic physicists, cosmologists, astronomers and other scientists. Number of amateur astronomers affected: 200,...


6

Each of James Webb's mirror segments are adjustable through seven small motors, called actuators. Due to thermal variations, the segments do indeed need to be re-adjusted occasionally. Exactly how often is a compromise between desired image quality and valuable science observation time, as argued by Park et al. (2017) who develop a thermal model, but don't ...


5

Hubble is a telescope. This means it has a big mirror to gather light and focus it onto a small area, and a system of lenses and mirrors to magnify the image formed by the big mirror. Now, how far can you see? 100 miles? 1000? You'd be way out! The stars are already trillions of miles away. Without a telescope you can see the Andromeda galaxy, which is ...


5

I can't detect you simultaneously! I have no way of knowing if you are alive or dead, as you are not in the same room as me I can assume you must be at least 10 meters from me. That means you are more than 30 light-nanoseconds If you have died in the past 30 nanoseconds, I could not know about it! However 30 nanoseconds is a very short period of time, ...


4

Sky-glow is a generic term for the diffuse light not due to the sun, moon or stars (or aurorae, I suppose). Much of it is light pollution from the ground, some is the zodiacal light from dust in space, and the coolest part may arguably be the air-glow from chemical reactions in the upper atmosphere. So, depending on height the different components would ...


4

The high density of energetic charged particles causes problems for any instrument system transiting through the South Atlantic Anomaly. Here, for example, is a description from the Hubble Space Telescope WFC3 Instrument Science Report 2009-40 (Barker et al. 2010, "WFC3 IR SAA Passage Behavior") of its effects on HST: The South Atlantic Anomaly (...


4

Hubble was designed in the late 1980s, when electronic detectors were small (the original Wide Field/Planetary Camera had two different 2x2 arrays of 800x800-pixel CCDs); it also had to carry multiple different instruments, each taking up nominal space in the focal plane. So it was optimized to use small fields of view to go with the small detectors. WFIRST/...


4

The JWST images will have various artifacts. I found a web page that summarises the situation for the Near Infrared Imager and Slitless Spectrograph (NIRISS). The image below (taken from that webpage) shows simulated point sources as they would appear on the detector (including the sampling by the 0.0656 arcsec pixels). The greyscale is on a logarithmic ...


4

Short answer, yes, the x-ray grazing incidence mirrors set up like this still function like a Cassegrain to minimize off-axis aberration. However, it is still different in that a classical Cassegrain uses a fast positive paraboloid and a slow negative hyperboloid. The Cassegrain design combines the paraboloid and hyperboloid to minimize off-axis aberrations ...


4

Space telescopes are expensive. However they have advantages "Permanent" night time, often they use a solar shade to stay dark to observe ambient light Also the biggest advantage is no atmosphere means no atmospheric distortion But the benefits come at a price. A amateur astronomer can build a telescope for money, homemade setups in the 10-100 ...


4

Sources above: https://www.facebook.com/NASAWebb/photos/10158883840795049/ below: https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-telescope Do telescope measurements (in meters, usually) measure in a straight line, from edge to edge, or follow the curve of the mirror? The short answer is @JamesK's; it's the straight-line diameter of whatever ...


4

As the Wikipedia page on VLBI interferometry points out, there have been a few spacecraft with radio antennae which have formed (along with ground based stations) part of radio interferometer networks. The examples given are the KRT 10-m dish on the Salyut space station, and the HALCA and Spektr-R satellites. The latter was in an orbit with an apogee almost ...


3

I will have to look for a source for this, but basically the best way to search for small NEOs is to use image at thermal infrared wavelengths. At circa 1 AU the Sun illuminates them with about 1600 watts per square meter. They are generally quite dark, which makes them hard to spot looking at reflected sunlight, and since they are against a background of ...


3

How much are the benefits of installing a telescope in orbit? In the past the benefits have been astronomical! Sorry, I couldn't help it. ...our atmosphere acts like a protective blanket letting only some light through while blocking others... For visible light astronomy, much of the light above the Earth reaches the ground, but astronomical seeing has ...


3

and I've read that Hubble uses a digital camera to take pictures like a cell phone. I can't find a place in nasa.gov that says that the Hubble works like a cell phone, but of course the principle is the same. An optical system takes parallel light coming from various directions and focuses each parallel bundle to a small point. We used to say this is how a ...


Only top voted, non community-wiki answers of a minimum length are eligible