- Why are images of bright stars and some other objects not allowed?
- My observation request has been in the queue for a while, why has not not been completed?
- How does the telescope decide what requests to observe?
Why are images of bright stars and some other objects not allowed?
The short answer is that bright stars (and stars contained in some other objects) are too bright for our large telescope and they will be overexposed, even when the shortest exposure time is used.
The long answer is:
- images containing bright stars will be overexposed and leave ghost images that are visible on subsequent images taken by the telescope. In a shared telescope, we cannot allow that to happen.
- some objects, such as large or bright star clusters, contain individual stars that are too bright. An example object in this category is the Pleiades star cluster.
- if you have an educational or scientific reason to observe a bright star, contact a #human.
- the telescope will automatically reject observations of stars brighter than magnitude 4.0 and any other observation where a star brighter than magnitude 3.5 is in the same field of view.
This could be for a number reasons. First of all, you can check your place in the queue anytime here or by using the #myrequests command. Recent requests are towards the top and older requests are towards the top. To find all of your requested and completed observations, go here and search for your name.
In general, observations are run in order from oldest to newest, but there are several other factors that decide when an observation is run.
The most important factor is the need for clear skies at night! In Halifax, we typically get only 2-4 nights a week with the skies clear enough for part or all of the night. In some times of the year, it may be cloudy for weeks at a time! And the clear skies available may not have occurred at the time of night needed to observe your request!
Another factor is the choice of object - if an object is only visible for a short time each night, it competes with other observations observable at the same time. This "competition" isn't always fair! as some observations or observers have been given elevated priority.
For more details on how the telescope's programs decide when to run an observation, see the next FAQ.
When the telescope is running, the skies are clear and dark, and it is about to run an observation, the first thing it does is scan through the entire observation request queue to see which requests can be observed right now. The factors it checks include:
- that the object's altitude is sufficiently above the horizon to clear local obstructions (trees, the owner's house, etc.) at both the beginning and anticipated end of the observation is ok
- that the anticipated end of the observation will complete before morning twilight begins
- that the Moon is not too bright and is not too nearby in the sky
From the list of observable requests a "points game" is then played and the observation request with the highest score is run! The factors scored include:
- a benefit for older queue entries - older requests are favoured over more recent requests.
- a benefit for objects with limited visibility - objects that can be observed tonight for a shorter time than others are favoured.
- observer priority - each observer is assigned a priority, either more or less than the default. This is used to give those working on special projects greater priority.
- group priority - observers are assigned to observer groups and each group can be assigned a priority, either more or less than the default.
- observation priority - each observation request can be given a priority, either more or less than the default.
- same or opposite side of pier - our telescope is attached to what is known as a German Equatorial mounting. That means that it has to "flip" sides when moving from the east-to-west or west-to-east sides of the sky. This takes a minute or two to complete, so a penalty is applied if applicable.
- distance from current telescope position - objects near where the telescope is currently pointed are slightly favoured.