Department of Physics AstroLab

Questions for AstroLabers (Part 1)

  1. What is the Right Ascension (RA) and Declination (Dec) co-ordinate system? What units are used in each direction? Why is one second of RA a different size to one second of Dec?

  2. Looking South from Durham (latitude = 55° N) at an angle of 35° above the horizon which are the directions of increasing RA and Dec?

  3. Why do astronomical charts usually have the North-East direction in the top left-hand corner rather than in the top right-hand corner? Precisely how long in hours, minutes, seconds does the Earth take to rotate relative to the `fixed' stars?

  4. What is local sidereal time and why is it important for observing? What will be the local sidereal time tonight at 20:00? What RA will be on the meridian tonight at 20:00 ?

  5. If your target field crosses the meridian at 22:00 hours tonight, at what time will it cross the meridian: (a) tomorrow night, (b) in a weeks time and (c) in month?

  6. What is the ecliptic? Roughly what is the RA and Dec of the Sun on 21st March, 21st June, 21st September and 21st December?

  7. What RA will be on the meridian at midnight on about 21st March, 21st June, 21st September and 21st December? What RA will be on the meridian at midnight tonight?

  8. When does your target rise/set and cross the meridian today? Why is it crazy (stupid) to observe your target at low altitudes (i.e. at a large airmass near the horizon)?

  9. At Durham (latitude = 55° N) on the solstices (~21st December and ~21st June) roughly at what compass points does the Sun rise and set? Also at these dates roughly how long is the Sun above the horizon?

  10. For objects located at Dec = −23.5° and Dec = +23.5°, roughly how long do they spend above the horizon? Roughly what is highest altitude these objects reach as seen from Durham? Hence why is better to select targets at high Dec?

  11. How many degrees per day does the Moon move relative to the `fixed' stars? On average how much later does the Moon rise each day? At what dates during term will the Moon be too bright and/or too close to your target(s)?

  12. What is astronomical seeing and how does it affect your observations? How is this likely to depend on the angle above the horizon of the observations?

  13. What limits the FWHM PSF ( Full-Width-Half-Maxmimum Point-Spread-Function ) that you are likely to achieve with your observations?

  14. How does a CCD work? What is Read(out) noise? What is a CCD's dark current/count? What is a dark frame? What is the A/D gain? Why does the CCD's 16-bit A/D converter result in a saturation level of 65535 ADU?

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