Successful Observing

You've selected an object that you really want to observe, and you want it tonight. That's all well and good, BUT, before you head off for the telescope (or send in your request), you will need to make sure that a) the object is actually observable on that night, b) and, if it's observable, when does the optimum observing window occur. This means that you will need to know the time of sunset, sunrise, the end and beginning of twilight to determine how many dark hours are available for observing. You will also need to know what part of the sky is visible during the night. Finally, you also need to know how long an exposure to take of your object: too long and the image could be saturated, too short and the object might be too faint.

Here are some tools to help you plan your observations.

The exposure time calculations depends on the signal to noise ratio you wish, the characteristics of the instrument (telescope plus camers) and the object's magnitude (brightness).

• Calculate the Exposure TImes
  
  To find the daily almanac for a site, you need to know an observatory's latitude and longitude and elevation. The Daily Almanac will provide sunrise, sunset, twilight, moon rise, moonset, moon phase and the local sidereal time at local (to the observatory) midnight for a given day. The sky calendar does the same but for a month at a time.
  
  
• Calculate the Daily Almanac
  
  
• Get the Sky Calendar
  
  You can determine when your object(s) will be above the horizon (up) using either a planetarium program on your computer (the kind with a graphical display) or a more traditional, command-line kind of program. You will rapidly find that most planetarium programs are good for displaying the position of an object for a given night, but that it becomes quite tedious to carry this through for an observing window that is longer than a few nights.
  
  One such program you might find useful for figuring out some of your observations for the LBNL RIT is ShowSKY (click here to look at it) which uses Distant Sun's software. In general, however, I recommend using a program like this next tool to calculate the optimum observing window for your object. You will need to know the latitude, longitude and elevation (in meters) for the observatory, and the right ascension (RA), declination (DEC) and epoch for your object. You also need the date that you want to take the observation. This tool will calculate the airmasses over the night for your object. The program will provide you with the hour angle (HA), secz (airmass), parallactic angle, as well as the moon's altitude for each hour. The best time to observe your object is when its airmass is smallest, between secz of 1 and 2, AND, when the HA is between 0 and 3 hrs.
  
  
• Calculating Airmasses
  
  If you want to know the long-term observability of your object, i.e. over a period of months, try using this: Observability . This is especially useful if you're interested in repeated observations of the same object over several weeks or longer, or if you're not certain when during the year your object is observable at a given site. Again, you will need to know the observatory/telescope latitude, longitude, elevetion (in meters), the object's coordinates, and provide a start and end date.

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