ASP Observational Techniques and Telescopes 2 — Questions and Answers
Question 1: What is the magnitude scale in astronomy?
- A scale measuring telescope sizes
- A logarithmic scale of stellar brightness where lower numbers indicate brighter objects (Correct answer)
- A scale measuring the size of galaxies
- A measurement of stellar distance in parsecs
Correct answer: A logarithmic scale of stellar brightness where lower numbers indicate brighter objects
The magnitude scale is a logarithmic measure of brightness where each step of 1 magnitude corresponds to a brightness ratio of ~2.512, with lower (and negative) numbers indicating brighter objects.
Question 2: What is the difference between apparent and absolute magnitude?
- Apparent is visual, absolute is measured by instruments
- Apparent is how bright a star looks from Earth; absolute is its intrinsic brightness at 10 parsecs (Correct answer)
- Apparent magnitude measures blue light, absolute measures all wavelengths
- Apparent is for stars, absolute is for galaxies
Correct answer: Apparent is how bright a star looks from Earth; absolute is its intrinsic brightness at 10 parsecs
Apparent magnitude is how bright an object appears from Earth, while absolute magnitude is its intrinsic brightness defined as the apparent magnitude it would have at a standard distance of 10 parsecs.
Question 3: What is a charge-coupled device (CCD) in astronomy?
- A device that amplifies radio signals from space
- A highly sensitive electronic light detector that converts photons to electrical signals (Correct answer)
- A camera filter used to block specific wavelengths
- A device that measures the angular size of stars
Correct answer: A highly sensitive electronic light detector that converts photons to electrical signals
A CCD (charge-coupled device) is a silicon-based electronic detector that converts incident photons into electrical charges with high quantum efficiency (~90%), revolutionizing astronomical imaging and replacing photographic plates.
Question 4: What is photometric redshift?
- Measuring redshift using prism spectroscopy
- Estimating galaxy redshift from broadband photometry using color information across multiple filters (Correct answer)
- The redshift caused by a star's photosphere temperature
- A direct measurement using the Doppler effect
Correct answer: Estimating galaxy redshift from broadband photometry using color information across multiple filters
Photometric redshift estimates a galaxy's distance by fitting its observed colors across multiple broadband filters to spectral energy distribution templates, yielding an approximate redshift without time-consuming spectroscopy.
Question 5: What is the purpose of a coronagraph?
- To measure solar corona temperatures
- To block out the central bright source so faint nearby objects like exoplanets or the solar corona can be observed (Correct answer)
- To enhance the contrast of galaxy cores
- To filter ultraviolet light from solar observations
Correct answer: To block out the central bright source so faint nearby objects like exoplanets or the solar corona can be observed
A coronagraph is an optical device that blocks the direct light from a bright source (like a star) to allow observation of much fainter nearby objects such as the solar corona, circumstellar disks, or exoplanets.
Question 6: What does 'seeing' refer to in ground-based optical astronomy?
- The visual acuity of the observer
- The stability and clarity of Earth's atmosphere that affects image sharpness (Correct answer)
- The limiting magnitude of a telescope
- The field of view available at a given magnification
Correct answer: The stability and clarity of Earth's atmosphere that affects image sharpness
Astronomical seeing refers to the blurring and twinkling of celestial objects caused by turbulence in Earth's atmosphere, typically measured in arcseconds; better seeing means less turbulence and sharper images.
ASP Observational Techniques and Telescopes 2
What is the magnitude scale in astronomy?