The Measure Inspector

When you focus on an image in the Editor, the Measure Inspector along the right side of Observatory’s window allows you to obtain more information from the image pixels themselves.

Measure Inspectors
Measure Inspectors

The inspector is organized in sections. You can collapse sections you are not interested in. You can also reorder the sections, but putting your mouse cursor between the disclosure triangle and section title, and clicking/dragging the section up or down to another position.

The Match… button towards the bottom of the inspector is equivalent to choosing Image ▸ Match… (⌃⌘M). Click it to plate solve the image. If the image already has been plate solved, the Unmatch button is displayed instead, which is equivalent to Image ▸ Unmatch. It is recommended to plate solve your non-calibration images, because it enables many features of Observatory (overlays, automatic tagging, etc).

The Cursor inspector

When you move the cursor over the image, this inspector will display the cursor’s position and the pixel value. In addition, if your image has been plate solved, it displays the right ascension and declination at the cursor position.

The Image Statistics inspector

This inspector displays the minimum, maximum, mean and median pixel values of the image. The number of pixels that were used for this may be less than the total number of pixels in the image, because Observatory skips invalid or missing pixels for these computations.

For an RGB image, the inspector displays the range of these values over the red, green and blue channels. To see the values for one channel only, select it in the Channels panel.

If you click the Reset button (the curly arrow) in this inspector, the inspector will toggle between a centered 100×100 pixel selection, and the complete image. Use this to compare the overall statistics with that of the center of the image.

Click the HUD button (the circle with two dots) in the inspector to make the selection rectangle visible in the Editor. You can click and drag it around, resize it from each end and corner. The mouse cursor changes its shape depending on the cursor position. The image statistics are refreshed each time you pause the dragging. You don’t need to release the mouse button, just pause the dragging itself.

Click the HUD button again to hide the selection from the Editor canvas.

The Photometry inspector

This inspector allows you to perform basic aperture photometry and Gaussian PSF fitting on your image.

For an RGB image, the first thing you should do is select the channel for which you want this to be measured. If you don’t, then the displayed values will be an average of the red, green and blue channels. Select the channel in the Channels panel.

Then, you should adjust the centroid settings in the Editor Bar such that the aperture is at least 3 times the FWHM as displayed in the Editor Bar for the to be measured stars. Also adjust the gap and annulus such that it contains mostly background pixels. You may deviate slightly from this to ensure that there are not multiple stars inside the aperture.

Now click the HUD button in the inspector. You will see two circular markers appear at the center of your image, initially on top of each other. You can drag these around and place them on the stars you want to measure (they “snap” in place when they detect a star). One is labeled V, and the other is labeled C. Far easier than dragging them, is just clicking on a star, which places V, and Option-clicking on the comparison star, which places C.

You will see that Observatory fills in many values in the Photometry Inspector when you do. If you know the magnitude of C, fill it in, and Observatory computes that of V.

If the image has been plate solved, the Photometry Inspector will automatically attempt to provide the magnitude of the selected comparison star from the Tycho–2, UCAC4 or USNO-A2.0 catalogs.

Displayed in the inspector are:

Click the HUD button again to hide the markers.

Photometry Inspector
Photometry Inspector

The Astrometry inspector

Use this inspector if you wish to measure positions of stars in your image, their mutual distance and position angle. Although not required, it is best to plate solve the image, because only then will Observatory be able to compute it all.

For an RGB image, the inspector uses the average centroid positions over the red, green and blue channels. To obtain the results for a single channel only, select it in the Channels panel.

As with the Photometry inspector, make sure to adjust the centroid settings in the Editor Bar to obtain the best results.

Click the HUD button, and position or move the circular markers as described above. Click on a star to place A, and Option-click on a star to place B.

The inspector displays:

Astrometry Inspector
Astrometry Inspector