Do professional observatories Schedule serious observations in the twilight hours of each night? Furthermore, how many of those observations at twilight are at 30° above the horizon or lower?
Quote from: Stan-1967 on 10/20/2019 08:46 pmDo professional observatories Schedule serious observations in the twilight hours of each night? Furthermore, how many of those observations at twilight are at 30° above the horizon or lower?The twilight is usually used for calibration. Since the sky has a very uniform brightness during twilight (at least on the scales a telescope operates), it is used to make twilight flats. I am not aware that science data is taken in these hours.The ESO telescopes in Chile open their dome about one hour before sunset. This is done with a person in the dome for trouble shooting. Its done one hour before sunset to have enough time to fix something in case its necessary. For example if the slit gets stuck, they can fix it before any valuable time is used. Once open, the telescope sits until sunset. The position of the telescope is actually locked to prevent sunlight hitting the primary mirror (which has the danger of destroying anything it illuminates). Twilight lasts a bit more than an hour after sunset and begins a bit more than an hour before sunrise.Observations below 30 degrees are usually not done since the atmosphere is too annoying. Its possible but people tend to avoid this.
Most telescopes can deal with that, says Olivier Hainaut, an astronomer at the European Southern Observatory (ESO) in Garching, Germany. Even if more companies launch megaconstellations, many astronomers might still be okay, he says. Hainaut has calculated that if 27,000 new satellites are launched, then ESO’s telescopes in Chile would lose about 0.8% of their long-exposure observing time near dusk and dawn. “Normally, we don’t do long exposures during twilight,” he says. “We are pretty sure it won’t be a problem for us.”But an upcoming, cutting-edge telescope could be in bigger trouble. The US Large Synoptic Survey Telescope (LSST) will use an enormous camera to study dark matter and dark energy, asteroids and other astronomical phenomena. It will survey the entire visible sky at least once every three nights, starting in 2022. Because the telescope has such a wide field of view, satellites trailing across the sky could affect it substantially, says Tony Tyson, an astronomer at the University of California, Davis, and the LSST’s chief scientist.He and his colleagues have been studying how up to 50,000 new satellites — an estimate from companies’ filings with the US government — could affect LSST observations. Full results are expected in a few weeks, but early findings suggest that the telescope could lose significant amounts of observing time to satellite trails near dusk and dawn.
An example of the impact. Obviously, this will get better as the satellites orient themselves correctly and disperse to their final orbits.https://twitter.com/lcjohnso/status/1196370554414125056--- Tony
Quote from: jebbo on 11/18/2019 11:28 amAn example of the impact. Obviously, this will get better as the satellites orient themselves correctly and disperse to their final orbits.https://twitter.com/lcjohnso/status/1196370554414125056--- Tony"example" is misleading. To get this shot, you have to aim, time, and choose your location very carefully...The satellites are lit against a dark sky only near sunset/sunrise, or for longer times when low on the horizon in the direction of the sun. Neither of these scenarios make for acceptable observing conditions.Also, when grouped together, they are only affecting one region at any given time... So you really have to get them intentionally for a picture like this.So this is "a shot of the satellite train", not "an example of impact on astronomy".
Quote from: meekGee on 11/18/2019 02:29 pmQuote from: jebbo on 11/18/2019 11:28 amAn example of the impact. Obviously, this will get better as the satellites orient themselves correctly and disperse to their final orbits.https://twitter.com/lcjohnso/status/1196370554414125056--- Tony"example" is misleading. To get this shot, you have to aim, time, and choose your location very carefully...The satellites are lit against a dark sky only near sunset/sunrise, or for longer times when low on the horizon in the direction of the sun. Neither of these scenarios make for acceptable observing conditions.Also, when grouped together, they are only affecting one region at any given time... So you really have to get them intentionally for a picture like this.So this is "a shot of the satellite train", not "an example of impact on astronomy".It's close to the summer solstice in Chile, so Starlinks will be visible for a good part of the night. At 550 km they would be visible nearly all night, but the ~300 km deployment altitude will greatly reduce the times then the "train" is visible. But as long as SpaceX is releasing the latest orbital data, which they are doing now, it's pretty trivial to predict a pass like this several days in advance and plan around it.
example" is misleading. To get this shot, you have to aim, time, and choose your location very carefully...The satellites are lit against a dark sky only near sunset/sunrise, or for longer times when low on the horizon in the direction of the sun. Neither of these scenarios make for acceptable observing conditions.Also, when grouped together, they are only affecting one region at any given time... So you really have to get them intentionally for a picture like this.So this is "a shot of the satellite train", not "an example of impact on astronomy".
And otherwise some proper software-guided masking technology can blot them out.
Astronomers do not own the heavens. They will have to learn to deal with a new reality.
Even 40,000 sats, say 200 planes of 200, represent a mesh of satellites 200 km apart. At an altitude of 300 km, that's 40 degrees apart to an observer on the ground. (LSST is under 4 degrees)So except for near the horizon (where you view the shell edge on) you'll have a hard time catching even one satellite, even if it happens to be lit, which is rarely to begin with.
It will not be that "there are satellites everywhere you look". There are about as many satellites planned as there are airplanes aloft, and the airplanes have nav lights and are concentrated over land.
It's close to the summer solstice in Chile, so Starlinks will be visible for a good part of the night. At 550 km they would be visible nearly all night, ...
Quote from: meekGee on 11/18/2019 03:55 pmIt will not be that "there are satellites everywhere you look". There are about as many satellites planned as there are airplanes aloft, and the airplanes have nav lights and are concentrated over land. Observatories have agreed no fly zones with the airlines for exactly this reason, and also have protocols to ensure safety if an aircraft strays too close (e.g. shutting down those AO lasers).--- Tony
Radio astronomers observe celestial objects in a wide range of frequencies for VLASS, and the strongest sources of interference just happen to be the geostationary Sirius/XM satellites. I appreciate having satellite radio available when driving through the southwest desert, but, on the other hand, it makes my role as VLASS scheduler extremely complicated!There are two different locations of Sirius/XM satellites in the sky. Their radio signal is so strong that we must take care not to point anywhere within a radius of about 15 degrees from either satellite location. This means that there is a 30-degree-wide strip of sky (nearly one-third of the sky visible from the VLA) that passes close to the satellites every day. Those regions of the sky must be scheduled for observations when they are low to the horizon: shortly after they rise in the east before that patch of sky rotates close to the satellites, or shortly before they set in the west. In reality, the map of positions where the VLA can point to avoid the satellite RFI is fairly complex. We have performed “sweeps” of the sky in order to measure the level of interference for different observation directions with the VLA.By planning and plotting, we can circumvent where we know these satellites are in the sky— they are always in the same sky direction with respect to the VLA, by definition, because they are in geosynchronous orbits (which means the satellites have a period of rotation synchronous with that of the Earth’s rotation).
Everybody forgot radio astronomy.This constellations will be devastating, at least in their current emitting bands.https://public.nrao.edu/blogs/interference-from-a-busy-planet/
Beasley said that SpaceX, while a concern to optical astronomers, has not been a source of worry for radio astronomers.“SpaceX set an excellent example on being responsible and trying to listen and deal with the issues that have come up,” said Beasley. “Full marks to them.”
Quote from: daveklingler on 06/13/2019 06:29 pmNo one at SpaceX or any of the other would-be constellation providers asked me how I felt about losing the natural skyActually, they did. The submitted an application for permission to put up the constellation to the United States government. The government, in turn, then invited input from all its citizens about their plan. You had a chance to make this point before the constellation was approved.There was even a fair amount of talk on this very site about the application when it was open for public comment.
No one at SpaceX or any of the other would-be constellation providers asked me how I felt about losing the natural sky
Quote from: envy887 on 11/18/2019 02:37 pmQuote from: meekGee on 11/18/2019 02:29 pmQuote from: jebbo on 11/18/2019 11:28 amAn example of the impact. Obviously, this will get better as the satellites orient themselves correctly and disperse to their final orbits.https://twitter.com/lcjohnso/status/1196370554414125056--- Tony"example" is misleading. To get this shot, you have to aim, time, and choose your location very carefully...The satellites are lit against a dark sky only near sunset/sunrise, or for longer times when low on the horizon in the direction of the sun. Neither of these scenarios make for acceptable observing conditions.Also, when grouped together, they are only affecting one region at any given time... So you really have to get them intentionally for a picture like this.So this is "a shot of the satellite train", not "an example of impact on astronomy".It's close to the summer solstice in Chile, so Starlinks will be visible for a good part of the night. At 550 km they would be visible nearly all night, but the ~300 km deployment altitude will greatly reduce the times then the "train" is visible. But as long as SpaceX is releasing the latest orbital data, which they are doing now, it's pretty trivial to predict a pass like this several days in advance and plan around it.And otherwise some proper software-guided masking technology can blot them out.Astronomers do not own the heavens. They will have to learn to deal with a new reality.
