Scale in ArcSeconds?

[DavidBartlett]

Is there any way that I can find the scale in ArcSeconds directly on the Picture for the APOD?

[Chris Peterson]

Is there any way that I can find the scale in ArcSeconds directly on the Picture for the APOD?

Generally not. If you know the sensor details and the focal length of the lens, you can calculate the pixel scale. Those things can be found in the EXIF header if the image was made with a digital camera, and if the header was preserved. For most astronomical images, you usually need to perform a plate solve to recover the pixel scale, although this information is occasionally provided in the caption or in linked data.

[DavidBartlett]

Thank you Chris. Is there a standard pixel scale for the Hubble Advanced Camera for Surveys?

[Chris Peterson]

Thank you Chris. Is there a standard pixel scale for the Hubble Advanced Camera for Surveys?

For the WCS, the plate scale is 0.05 arcsec/pixel. You have to be careful with released images, and those published on APOD, since they are sometimes resampled to different resolutions. Don't automatically assume you are seeing an image at the native resolution of the camera.