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Wide-Field Imaging

How does Pan-STARRS compare with other sky surveys?

For many applications, the rate at which objects can be detected scales as the etendue of the telescope, which is defined as the product of its collecting area (A) times the field of view (Ω).

The upper link on the right compares Pan-STARRS' field of view with that of several other instruments. The second link compare the entendues (AΩ) of several surveys with that of PanSTARRS. PanSTARRS will have an etendue at least 5 times better than that of any other instrument

How does Pan-STARRS observe?

Pan-STARRS' method of observation will be very simple. The telescope will point at a selected patch of sky for about 30 seconds, then download the images to a computer. Depending on the scientific requirements, it may then take another look at the same patch of sky using a different color filter, or more likely, it will move on to the next patch of sky, all under pre-programmed computer control.

How long will it take to survey the sky?

About three quarters of the total sky can be observed from Hawaii, or about 30,000 square degrees. Pan-Starrs will look at about 7 square degrees in each 30 seconds exposure, so in an eight-hour night it will be able to map about 6,000 square degrees. Given that the weather is not always perfect, it will therefore take about a week to survey the whole sky once, using one filter.

In practice, however, some parts of the sky will be surveyed more often than weekly, and some less often. Particular attention will be paid to those areas of sky in which potentially hazardous asteroids are most often found, and areas of the Galaxy and Universe that have been chosen for particularly close study.

How long will each exposure be?

The typical exposure time for a Pan-STARRS image will be around 30 seconds, depending on the filter used and the particular type of survey being carried out.

Longer exposures can detect fainter images, but have the disadvantages that (a) a full-sky survey would take longer than a week, and (b) the images of moving objects, such as asteroids, will smear and will therefore be less reliably detectable.

Exposures that are too short have the disadvantages that c) the read noise from the CCDs may become comparable to the intrinsic noise from the sky, and d) more exposures require more data handling.

How sensitive WILL Pan-STARRS BE?

A single observation with the broadband filter will reach a 5σ depth of 24 magnitude. This are type of observation will be used to search for solar system objects. By adding observations taken over several years, Pan-STARRS should be able to reach a maximum depth of magnitude 29.4.

Will Pan-STARRS be good for astrometry?

Yes, very good. We expect to be able to determine positions on an individual image to within 0.07 arcseconds, based on an image size of 0.6 arcseconds FWHM, and a signal-to-noise ratio of 5. Systematic errors should be less than 0.1 arcseconds over a 10 arcminute field. This high precision will make Pan-STARRS invaluable for proper motion and parallax observations of nearby stars, as well as of solar system objects.

Will Pan-STARRS be good for photometry?

Yes. Accurate photometry is crucial to the detection and measurement of variable sources and of star and galaxy colors. The goal for absolute photometric precision in stacked and difference images is 0.01 magnitudes. Higher precision should be attainable for relative photometry of brighter objects.

How often will you RETURN to the same region of sky?

Normal procedure will be to make observations of the same piece of sky a few tens of minutes apart, so that main-belt asteroids can be easily identified by their proper motions. More distant objects such as Kuiper Belt Objects are best detected on a timescale of a few days, while different kinds of variable stars show up better in observations separated by anything from minutes to weeks.

Is Pan-STARRS the same as the LARGE SYNOPTIC SURVeY Telescope (LSST)?

No. Pan-STARRS will have a smaller collecting area than the LSST as recommended in the decadal report. However, we expect that it will do much, but not all, of the science proposed for the LSST at something like 20-25% the cost of the larger project.

Next: Why four mirrors?

Orion image
Field of view

Etendue comparison

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