Astronomical Coordinate Systems, Distances, and Light Properties in Observational Astrophysics

What is the formula to calculate the angular separation between two objects in right ascension (RA) and declination (DEC)?

Δα = (α1 − α2) cos δ; Δθ2 = (δ1 − δ2)² + [(α1 − α2) cos δ]²

Given α1 = 3h30m, α2 = 2h30m, δC = 20°, and δD = 70°, which pair of objects has the smallest angular separation?

Pair C and Pair D need to be calculated to determine the smallest separation.

How can you find your latitude using the night sky in the Northern Hemisphere?

The elevation of the North Celestial Pole (NCP) gives your latitude.

What is the relationship between an object's distance from the North Celestial Pole and declination?

The distance of an object from the NCP is 90° - δ.

What is the Hour Angle (HA) of an object?

The angle of an object with respect to the meridian, calculated as HAobject = RAmeridian − RAobject.

What does a positive Hour Angle indicate about an object's altitude?

An object with a positive Hour Angle is increasing its altitude.

What is the significance of a sidereal day not being 24 hours long?

It relates to the Earth's rotation and its orbit around the Sun, affecting the timing of celestial events.

What is Local Apparent Solar Time?

It is the hour angle of the sun as it appears in the sky, plus 12 hours.

What is the difference between Local Mean Solar Time and Universal Time (UT1)?

Local Mean Solar Time is based on a fictitious mean sun, while UT1 is mean solar time at 0° longitude.

What does Coordinated Universal Time (UTC) account for?

UTC is corrected for non-uniformities in Earth's rotation rate.

What is airmass in astronomy?

Airmass is the amount of atmosphere that light from an object passes through to reach an observer.

What is the formula for calculating airmass based on zenith angle?

airmass = sec(z), where z is the zenith angle.

What elevation corresponds to an airmass of 2?

An airmass of 2 corresponds to a zenith angle of 30 degrees.

What is the parallax angle in astronomy?

The parallax angle (p) is the apparent shift of an object against a distant background due to the observer's change in position.

What is the formula for converting parallax angle to distance in parsecs?

p[arcsec] = 1/r[pc], where r is the distance in parsecs.

What is the relationship between parallax angle and astronomical units (AU)?

p[arcsec] = a[AU]/r[pc], where a is the semi-major axis.

How is a parsec defined in relation to astronomical units?

1 parsec (pc) = 206265 AU.

What is the significance of the GAIA satellite in astronomy?

GAIA can measure parallaxes to microarcseconds, enhancing distance measurement accuracy.

If an object has a parallax of 0.01 arcsec from Earth, how would it be measured from Jupiter?

The parallax would be different due to Jupiter's greater distance from the object.

What is the primary focus of the GAIA project?

To measure the positions and motions of stars in our galaxy.

How many stars were analyzed in the GAIA project?

65 million stars.

What is the significance of measuring tangential velocity?

It helps determine how a star's position changes over time.

What method is used to measure radial velocity?

Doppler Shift.

What does a positive radial velocity indicate?

The star is moving away from us.

What is the formula for radial velocity using Doppler Shift?

z = (λ_obs - λ_rest) / λ_rest.

What is the relationship between tangential motion and distance?

Tangential velocity is measured by proper motion in combination with distance.

What does proper motion measure?

The angular position change of a star over time.

What is a parallax ellipse?

The apparent annual path of a nearby star on the celestial sphere.

What is the purpose of astronomical databases?

To store raw or processed images, spectra, and measured properties of celestial objects.

Why might a researcher use an astronomical database?

To conduct science projects or check if a proposal idea has already been explored.

What is the Sloan Digital Sky Survey (SDSS)?

A large survey that provides accessible astronomical data.

What does the resolving power of a spectrograph determine?

The ability to measure small shifts in wavelength.

What is the significance of the GAIA archive?

It provides access to the full GAIA catalog of stellar data.

What type of data does the NASA Extragalactic Database (NED) curate?

Data related to galaxies.

What is the role of the Mikulski Archive for Space Telescopes (MAST)?

It serves as a clearinghouse for data from HST, TESS, JWST, and Roman archives.

What is the purpose of measuring the wavelength of spectral lines?

To determine the properties of astronomical objects.

What does the term 'proper motion' refer to?

The apparent motion of a star across the sky relative to more distant background stars.

What is the formula for the relativistic Doppler shift?

z = (1 + β) / (1 - β) - 1, where β = v_R / c.

What does the term 'Doppler shift' refer to?

The change in wavelength of light due to the motion of the source relative to the observer.

What is the significance of measuring the angular position change of a star?

It allows astronomers to track the star's motion over time.

What is the main advantage of using data from large surveys?

The data tends to be homogeneous and well calibrated.

What is the relationship between distance and proper motion?

Nearby stars have higher proper motions due to their relative motion across the sky.

What is the course title for Astronomy 596?

Observational Astrophysics

When are the lecture classes for Astronomy 596?

Monday, Wednesday, and Friday from 12:00 to 12:50 PM

Where is the lecture for Astronomy 596 held?

Room 3092 Malott

What is the first module topic in the course?

The Nature of Light from an Astronomical Perspective

What is the required textbook for Module 1?

Mark Gallaway - An Introduction to Observational Astrophysics

What is due on Friday for Module 1?

Gallaway, Read 2-2.4 and Homework 1

What are the discussion section times for Astronomy 596?

Tuesday 10:00-10:50 AM and Thursday 12:30-1:20 PM

What is the purpose of the 'Getting Started' section in Canvas?

To provide guidance on how to succeed in the class

What is one of the important course components mentioned?

Nighttime observations with amateur telescopes

What is the significance of solid angle in astronomy?

It measures angular areas in a spherical coordinate system

What is the area of the sky in steradians?

4π steradians

What is the relationship between light and energy in the context of electrons?

Electrons are liberated from metals only if the light's wavelength corresponds to energy greater than the binding energy.

What properties of light are measured in observational astrophysics?

Wave properties (diffraction, refraction, reflection) and particle properties (detection of light at all wavelengths)

What is the nature of light according to the course material?

Light behaves as both a wave and a particle.

What is the purpose of the capstone project in this course?

To conduct a multi-part project in groups.

What is the deadline for the Intro survey in Module 0?

Due Friday at 11:59 AM

What is the significance of the 'observer's station' mentioned in the course?

It is a location where observational astronomers conduct their work.

What is one of the telescopes mentioned in the course material?

Jansky Very Large Array

What is the role of spectroscopy in observational astrophysics?

It relies on both wave and particle properties of light.

What should students do before attending the first class?

Read the syllabus and come with questions.

What is the purpose of group work in the class?

To encourage collaboration and respect among students.

What is an interesting fact about the instructor?

The instructor has spent roughly 8 years living and working in Germany.

What is the significance of the 'computer activities' mentioned?

They involve using the departmental computer lab for hands-on activities.

What is required to access the computer labs?

A room entry code that should not be shared.

What is the expected outcome of the 'Getting to Know You' survey?

To match the course to students' needs.

What is the role of light detectors in observational astrophysics?

To count photons and measure light intensity.

What is the definition of luminosity in the context of light?

The total light emitted from an object.

What is radiant exitance?

The flux leaving a unit surface area of a spherical object.

What is the formula for radiant exitance (s) of a spherical object of radius a?

s = L / (4πa²)

What is a solid angle?

The total angular area subtended by an object at a distance r, denoted as Ω.

What is the projected area of a spherical object with radius a?

The projected area is πa².

What is surface brightness?

The amount of flux spread over a solid angle, denoted as σ.

What are the common units for surface brightness?

flux/asec² and flux/steradian.

What influences how many photons a detector sees?

The intensity of light incident on the detector.

What is a spectrum?

When light is spread out into intensity at different wavelengths.

What is the formula for intensity between frequencies ν and ν + dν?

F(ν, ν + Δν) = fν ≡ F(ν, ν + dν) as Δν approaches 0.

What is monochromatic flux?

The specific flux at a single wavelength or frequency, denoted as fλ or fν.

What is Wien's Law?

λmax [m] = 2.9 × 10⁻³ [m K], relating the peak wavelength of thermal emission to temperature.

What does the peak of the thermal emission curve indicate?

It indicates the object's temperature and color.

What happens to the shape of spectra when plotted differently?

The shape changes depending on whether it is plotted as fν or fλ.

What is the integral of a spectrum used for?

To calculate the total intensity of an object over a specific wavelength range.

What components contribute to the response function R(λ)?

Atmosphere, mirror reflectivity, filter throughput, and detector efficiency.

What is the average flux density within a given bandpass?

⟨Fλ,detected⟩ = ∫ fλ Rsys(λ) dλ.

What is the significance of Vega in astronomical measurements?

Vega is one of the only stars with an absolute flux measurement, used as a reference.

What is the relationship between fλ and fν?

fλ dλ = fν dν, indicating their dependence on wavelength and frequency.

What is the effect of integrating a curve in a spectrum?

It gives the area under the curve, representing total intensity.

What is the formula for detected flux through a filter?

Fdetected = ∫ fλ R(λ) dλ.

What is the typical behavior of the thermal emission curve?

It behaves differently on both sides of the peak wavelength.

What is the significance of the solid angle in astrophysics?

It quantifies how much of the sky an object occupies from a given point.

What is the small angle approximation for solid angle?

Ω ≈ πa² / r² for small angles.

What does the term 'system response' refer to in telescopes?

The combined detection efficiency of light at different wavelengths.

What is the common range for Near Infrared (NIR) wavelengths?

1.0 to 2.5 μm.

What is the formula for the flux incident on a filter?

Fincident(λ1, λ2) = ∫ fλ dλ from λ1 to λ2.

What does the term 'detector throughput' refer to?

The efficiency of a detector in converting incident photons into a measurable signal.

What is the formula for linear flux expressed in erg/s/cm²/Å?

fλ = 3 × 10−12 erg/s/cm²/Å

How is flux often expressed in log units?

log (fλ/(erg/s/cm²/Å)) = −11.52

What reference star is commonly used for brightness comparison?

Vega

What is the relationship between magnitudes and flux?

m1 − m2 = −2.5 log (f1/f2)