1. What is Declination (Dec)?
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- If we imagine the Earth at the centre of a giant celestial sphere, declination is almost identical to Latitude.
- It is a projection of latitude onto the sphere.
- It is the angle of a point above the celestial equator.
- The Declination of a star never changes!
2. What is Right Ascension?
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- The RA of a star is the angle between it and the celestial prime meridian.
- It is measured in hours and minutes.
Click here for an interactive demonstration of the celestial sphere.
3. What is the Celestial Prime Meridian?
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- This is the point on the celestial equator on which the sun moves from the southern to the northern hemisphere.
- Spring Equinox (March 21st)
4. What is the Zodiacal Band?
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- This is the part of the sky that contains the constellations of the zodiac and is the region in which the planets and Moon are located.
- It straddles the Ecliptic by 8 degrees on either side.
5. How do you find your latitude using Polaris?
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- Measure the angular elevation of Polaris from the Northern Horizon
6. Which way do stars appear to rotate about Polaris?
7. How can we determine if a star will be circumpolar using the observer’s latitude and the star’s declination?
8. What is a circumpolar star?
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- This is a star that does not set.
- It is above the observer’s horizon all the time.
- Which stars are circumpolar depends on the observer’s horizon.
9. Explain how a star will be circumpolar from a given latitude so long as the declination is > 90 -latitude.
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- My latitude is 52 degrees.
- 90-52 = 38 degrees
- Therefore any stare with a declination >38 degrees will be circumpolar.
- The diagram below explains this further.
- Any star with a declination of 52 degrees will be at my Zenith
10. Name 4 considerations when planning an observation.
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- Phase of the moon
- Ideally not visible or less than half
- Check weather Forecast
- Likely-hood of a meteor shower
- Visibility of a planet, Messier/comet.
2. Equipment
- Torch with red filter
- Does not have such an adverse effect on dark adapted eyes.
- Reclining chair or table
- Warm clothes
- Planisphere
11. What else is ideal for observing stars?
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- Dark adapted vision
- 20-30mins of darkness allows retinas rods to become most sensitive
- Relaxed eye
- Averted vision
- Focus light onto more sensitive rods
- e.g. M31
12. Who was Charles Messier?
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- Compiled a list of 110 “fuzzy” objects in the sky.
- Named “Ferret of Comets”.
