SkyView includes WMAP Nine Year Data

We have updated SkyView to use the new nine year maps for WMAP. These represent the full mission dataset for the Wilkinson Microwave Anisotropy Probe. The structure is unchanged from the earlier 7 year data. We provide a total of six surveys. These include five frequency bands and the WMAPILC survey which uses multiwavelength data to remove any contribution from the Galaxy.

WMAP data internally uses HEALPix data formats and so currently WMAP may only be accessed through our web interface. However a remote user can download the raw data from the LAMBDA where users can download both the frequency maps and the ILC image and can then use those images as user-defined surveys with the SkyView jar.

This is expected to be the last major change to the WMAP mission data.

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UKIDSS surveys to be added to SkyView

Early in January 2013 we shall be adding access to the UKIRT Deep Infrared Sky Surveys (UKIDSS). Their web site describes these surveys as the successor to 2MASS. Ultimately they will cover about 7,000 square degrees, or a bit more than one sixth of the sky. UKIDSS goes about 3 magnitudes deeper than 2MASS (a factor of ~15 in brightness) and has substantially higher resolution.

SkyView will use the public UKIDSS data which currently are release DR7.

The UKIDSS data that we will include to includes four bands, Y, J, H, and K which range in wavelength from about 0.97 to 2.37 microns, or in frequency from 310 to 126 THz. Only limited Y band coverage is available. Survey resolution is 1″ and pixels are 0.4″ on a side.

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SDSS update

The FITS headers generated by the SDSS surveys will now reflect that these are using DR9 data rather than DR8 results. The SDSS site switched to using DR9 a couple of weeks ago. We’re told the primary difference is improved astrometry in the DR9 data.

Note that future SDSS releases are not expected to have significantly greater sky coverage.

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SDSS DR9 release

It appears that the SDSS servers have begun serving SDSS DR9 data. SkyView accesses the SDSS through the Virtual Observatory Simple Image Access protocol (SIAP). In this protocol a user first requests a list of the images available in a region and a set of available URLs is returned.

As discussed in the previous article, the initial call for the list of URLs was working, but it appears that the URLs that were being returned have been a format they no longer supported. This may have been the case since September. The SDSS servers are now returning valid URLs but even though we are still querying using the URL for the DR8 SIAP service, the URLs being returned are for DR9 files. Thus images produced in the surveys labeled SDSSx in the SkyView interfaces are now DR9 although the documentation and internal FITS contents suggests that they are DR8. These will be updated early next week.

Access to the SDSSx surveys will likely be slower than normal until the SDSS cache is rebuilt using DR9 files.

Access to the SDSSDR7x surveys has been unaffected by these problems. It uses a different set of servers than the more recent releases.

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WISE and SDSS problems

Recently we’ve had some problems with access to the WISE and SDSS surveys (but not the SDSS DR7). We access these remotely using a standard protocol where we first find a list of the images in the region of interest and then download the ones we want. For WISE the initial queries were failing which meant that all WISE requests failed. We notified IPAC of the problem and they quickly rectified it.

For the SDSS the initial query for the list of images works fine, but if we try to download any image file the request fails. This means that some SDSS SkyView requests will succeed and some may succeed partially. SkyView caches the results from remote queries, so if anyone had requested a particular image previously, we don’t try to download it again, we just use our cached copy.

Update: (12/13/2012)
Both the SDSS and WISE data have been restored. It appears that the SDSS changed their output format several months ago so that SDSS queries that requested new regions have been failing for some while — but since we had rather large amount of data in the cache many SDSS queries succeeded.

The SDSS surveys are now pointing to DR9 data and since we do not have these cached SDSS queries will generally slow down as we rebuild our local cache.

Only the surveys labeled SDSSx are affected. The SDSS DR7 release which uses different servers and returns data in a somewhat different format, seems to be working without any problems. However it has somewhat less total sky coverage than the DR8 release.

The SDSS team are aware of the problems are are working to fix them. We apologize for any inconvenience to our users.

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Can you help me find a star?

We often receive email messages asking for help finding a star. In this post we will give instructions for displaying an image of a star in SkyView, as well as provide further tips for finding the star on a star chart and determining the star’s constellation and one final note about purchasing a star.

Instructions for generating an image of a star:

1. To generate an image in SkyView you’ll need a set of coordinates – the star’s right ascension and  declination.  These are the stellar equivalent of the latitude and longitude on the Earth. These may be in various formats but the RA usually is given as three numbers – hours, minutes and seconds.  The first is between 0 and 23, the second between 0 and 59 and the third between 0 and 60.  The third number, the seconds, may  contain a fractional part.  The Declination is similar, but the the first number can range between -90 and 90 and is called degrees not hours.

For SkyView these coordinates may need to be converted to a format containing just hours, minutes, seconds or decimal numbers.  They can be separated by a comma or the sign for the declination (more information)

An example of a set of coordinates:    RA: 6h 39m 15.70s DEC: 2 16′ 22.7″

The SkyView format of this set of coordinates would be:

6 39 15.70, 2 16 22.17   or   6 39 15.70 +2 16 22.17

Coordinates in this format can be used in the SkyView Query form.

Enter the coordinates in the Coordinates or Source input box.


2. Next a SkyView Survey needs to be selected.  The SkyView Query form provides many surveys in many wavelengths.  Typically someone trying to find a star will want to see how it appears in the night sky so an optical survey is best.  The best survey to start with is the Digital Sky Survey (DSS) which is at the top of our DSS survey category.


3. Once at least one  survey is selected and coordinates are entered the user can click the Submit button and an image of the sky centered on the coordinates will be displayed.

Below is a partial  image of the SkyView Query Form showing the coordinates entered in the Coordinates or Source box and the DSS survey selected.  Below the form is an image of the star that displays after the form is submitted.

SkyView Query Form

SkyView Query Form

DSS image at 6 39 15.70 +2 16 22.17

SkyView Image centered at 6 39 15.70 +2 16 22.17

The SkyView Query Form has many other options for manipulating the SkyView image to change image size, image colors, resampling, projections, coordinate systems or to add contours and other overlays.  These are just a few of SkyView‘s features. An example would be the option to mark the center of an image with a circle. Apply this feature in the Overlays section of the Query Form (see below). Check the Image Center Reticule option before submitting the query.

skyview_query_reticule_image

skyview_query_reticule

Related Tips:

There are many websites that provide sky charts for a particular location and information about constellations.  Here are two of these sites  we have found useful:

http://djm.cc/constellation.html: A simple form that displays the name of the constellation for specified coordinates

http://vizier.u-strasbg.fr/vizier/VizieR/constellations.htx#q: Displays boundaries for constellations.  Enter coordinates below the list of constellations.

http://www.fourmilab.ch/yoursky: Get images of entire sky as viewed from a given location at a specified time and date.  Their Virtual Telescope shows constellations and other objects at specified coordinates.

http://www.heavens-above.com:  Get sky charts and satellite schedules as seen from specified locations. This site also gives the time in various time zones/formats (local time, GMT, UTC)

A Final Note:

Many of these requests for help finding a star come from people who have purchased or received a gift of a star from a registry service. No star registry services are recognized by any political or  scientific authorities.  More information can be found at http://www.iau.org/public/buying_star_names/

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VLSS Redux available through SkyView

The VLSS sky survey has been updated to use data from the VLSS redux analysis described in Lane et al 2012. There is a slight increase in sky coverage and resolution and a substantial improvement in the noise due to better handling of bias due to the cleaning algorithm, atmospheric effects, radio interference and bright sources.

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FITS Header Issue

In some cases SkyView has been including newline characters in FITS headers. This is a violation of the FITS standards and apparently confuses some tools about subsequent header records. We’ve put in a fix for the problem this morning (10/25) so this should be resolved. It looks like it mostly affected surveys where we had put in links to other other surveys (e.g., the ROSAT PSPC surveys).

Thanks to Todd Hunter for bringing this to our attention. If you see any problems with the system you can use our E-mail (skyview at skyview.gsfc.nasa.gov) to let us know about it.

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SkyView system downtime scheduled for October 27-28

A significant downtime is  planned for the weekend of October 27-28 to upgrade computer facilities.  HEASARC/SkyView services may be down for a substantial fraction of the weekend.

The downtime will start at 12:00pm EST Saturday October 27 and will last for about 24 hours. We apologize for the inconvenience.

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SkyView system downtime has been postponed

The system downtime previously scheduled for this weekend has been cancelled and tentatively rescheduled for no earlier than October 13-14, 2012.

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