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/

Posted in Discussion | 136 Comments

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.

Posted in Announce | Leave a comment

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.

Posted in Notices | Tagged , | Leave a comment

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.

Posted in Notices | 5 Comments

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.

Posted in Notices | Leave a comment

SkyView system downtime September 21-23

A significant downtime is currently planned for the weekend of September 21-23 to upgrade computer facilities.  HEASARC/SkyView services may be down for a substantial fraction of the weekend.  We apologize for the inconvenience.

Posted in Notices | Tagged | Leave a comment

Features in the Gallery: The GEICO Gecko?

One recent gallery entry shows — to me at least — a remarkable resemblance to the GEICO gecko.

or you can see it a lot bigger in its gallery entry.

This is a DSS blue image, and we don’t see anything at the same point in the DSS red.
So what is this If we zoom out a little we see this as an intense black region surrounded by a couple of bright spots. The bright spots don’t really look like stars — they have rings. My guess is that a couple of drops of some chemical got dropped on the plate and dissolved the plate emulsion. That left a just the glass in the central spot where we see the very black region. The DSS plates are scans of photgraphic negatives — so what we see as black is actually the most transparent region. As the drops dried out they became more circular and deposited the dissolved emulsion back on the glass plate, so the bright ‘stars’ are just the ‘sky’ that should have been seen in the black regions.

Or maybe someone’s selling flying saucer insurance for a savings of 15% or more.

Posted in Discussion | Tagged , | 2 Comments

WISE survey interruption

No access to WISE survey data was possible for much of today due to problems at IPAC. These have been resolved and WISE data should again be available through SkyView.

 

Posted in Notices | Tagged , , | Leave a comment

Approximate Projections and Raw Cutouts

One feature that we’ve added to the underlying SkyView code recently is the ability to create approximate projections.  Several surveys in SkyView, the DSSn and NEAT include distortions in the projection plane that mean that the data cannot be accurately represented as a simple projection.   However the standard FITS  WCS of an image allows for a general affine transformation so even though we cannot do make an exact WCS we can use the affine transformation to build an approximate WCS for the image that is correct to first order at the center of the image.  It’s relatively straightforward to compute the Jacobian of the distortion at the center of the user requested image and we simply need to add this to the existing WCS.  For a  DSSx the resulting WCS can be quite accurate over an image with a size of a thousand or more pixels.  For NEAT data the fit is almost always good at least to several hundred pixels.  Here I’m using very good to mean that the error is less than an arcsecond.

One use for this is to allow SkyView to return the raw pixels from a survey.  Of course this limits the ability to mosaic, but users sometimes want to get the data exactly as taken.  One concern about providing raw cutouts was that we couldn’t describe their geometry appropriately for some of the most commonly used surveys.  We’ll we looking at providing a ‘Raw’ projection in SkyView over the next few months.

Posted in Discussion, Notices | Tagged , , , | 2 Comments

Problems accessing WISE data

For the past couple of weeks SkyView has not been able access data from the WISE archive. SkyView queries for  WISE images in regions already in our cache worked fine, but users who requested a new region got back a blank image.    This behavior seems to have started around June 27.

The problem arose when WISE inadvertently changed the URL’s they published the data under (using the VO Simple Image Access Protocol) to a format that was really only intended for internal use.  In particular it used a non-standard port number, rather than the standard HTTP port 80. The firewall that our web servers are behind does not permit access to unregistered, non-standard ports, so our servers were unable to download new data.

The WISE team fixed the problem immediately upon being notified of it and all should be back to normal.  We apologize for the time it took to discover this problem.  The normal behavior requests in cached regions concealed the problem from our regular checks.

Posted in Uncategorized | 4 Comments