Category Archives: Observing Tips

Tips and techniques for observing

FLO Panorama 2018-02-10

I did a quick panorama for FLO to get a better idea of the skyline and obstructions. The view is from the mound just from in front of the telescope room door and facing south.  I have included two panorama images below – one as an annotated JPG and the other as a PNG with a transparent sky for use in chart applications . A few notes first.

I didn’t have my compass with me while taking the pictures, so i assumed the buildings were oriented North-South and used the “south” facing view as the location for 180° in the reference image. However, when i checked Google Maps it appears the buildings are lined up a little west of south.

FLO Google Maps Aerial 2018-02-10

FLO Google Maps Aerial 2018-02-10

The aerial picture for FLO in Google Maps is low resolution so it was a bit of guess to get a precise reading – something between 7° and 18° west of south. I went with 18° (azimuth 198°) and adjusted my reference image accordingly. Also, aligning the camera to the buildings was a bit of guess, so there is some additional error there.

Next time i am at FLO i will recheck the orientation with my compass and then update the panorama images accordingly.

The tree line directly south appears to be about altitude 22°. The trees to the south east are a little lower at 18°. The large tree to the south west is altitude 24° at azimuth 253° (assuming the i have south in the right place).

The full sized images are 7200 x 1132 px with a scale of 20 pixels / degree. South (az = 180°) is in the image centre at x = 3600 px and the horizon (alt = 0°) is at y = 832px (0,0 being at the left-top). It is of course a full 360° panorama. Skyline altitude and azimuth to other points can be calculated from the pixel location and image scale.

You can click on the images below to view and download the full sized images.

The annotated panorama:

FLO Panorama 2018-02-10 Annotated

FLO Panorama 2018-02-10 Annotated

The PNG file should be suitable as a horizon panorama for some chart applications (e.g. Starry Night Pro). Although meta data is usually required by the application to describe the image scale and orientation (see below). (Note that some browsers display PNG transparent areas as white. But a downloaded PNG file has an alpha channel and with the right viewer, the sky will appear transparent.)

FLO panorama 2018-02-10

FLO panorama 2018-02-10

The PC version of Starry Night Pro 7 horizon meta data file describing the above PNG file is FLO-panorama-2018-02-10. SNP also includes a thumbnail version of the panorama. The program may create this the first time the horizon is used. If not, just create a 256x64px version of the panorama PNG file.

Hand Scale for Measuring Angles

When describing how to find an object in the night sky, the location is often given as an angle from a bright, easy to find object. This is particularly true for “naked eye” and binocular objects where you don’t have a fancy GoTo computer controlled mount to point the telescope for you. Statements like “Mercury will be 2° below the moon on Oct 6th, 2013” may sound great, but what does 2° look like?

Hand_ScaleYou can get a pretty good approximation of an angle by using your own hand as a scale. Hold your hand up in front of the object, straighten your arm and use various parts of your hand to gauge the angles. This works for everyone since generally those with longer arms have larger hands – so the angles will be roughly the same.

With your fingers stretched open, the distance from the tip of your thumb to your pinky is about 20°. The distance across your palm is about 10° and a finger is about 2°.

You can also calibrate your hand scale by checking it against a known object. The Big Dipper asterism is very convenient for this since it’s a familiar object and visible most times of the year. The chart below shows the distances between some stars: 4° – two fingers, 10° – palm and 20° – tip to tip fingers.
Hand_Scale_Big_DipperWhile you’re looking at the Big Dipper, just for fun try to see the separation between Mizar and Alcor. They are about 11’ (1/6 of a degree) apart which is about the limit of normal vision. These two stars are part of a multiple star system that revolve around each other (in a few hundred thousand years).

So if you wanted to find Mercury when it’s 2° from the moon, line up the side of your finger with the moon and Mercury will be just on the other side.