# answers for 180 astrophysics questions

Q9. Briefly describe the following kinds of astronomical instruments and their purpose: Schmidt camera, echelle spectrograph, CCD, III aJ emulsion, proportional counter, H maser, aperture synthesis telescope, laser interferometer, tank of cleaning fluid.

• Schmidt camera: Its optical components are an easy-to-make spherical primary mirror, and an aspherical correcting lens, known as a corrector plate, located at the center of curvature of the primary mirror. The film or other detector is placed inside the camera, at the prime focus. The Schmidt camera is typically used as a survey instrument, for research programs in which a large amount of sky must be covered. Echelle spectrograph: A spectrograph is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials.
• CCD: A charge-coupled device (CCD) is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value.
• III aJ emulsion:
• Proportional counter: A proportional counter is a measurement device to count particles of ionizing radiation and measure their energy.
• H maser: An astrophysical maser is a naturally occurring source of stimulated spectral line emission, typically in the microwave portion of the electromagnetic spectrum. This emission may arise in molecular clouds, comets, planetary atmospheres, stellar atmospheres, or from various conditions in interstellar space.
• Aperture synthesis: Aperture synthesis or synthesis imaging is a type of interferometry that mixes signals from a collection of telescopes to produce images having the same angular resolution as an instrument the size of the entire collection.
• Laser interferometer: The Laser Interferometer Space Antenna (LISA) experiment is a joint venture of the European Space Agency (ESA) and NASA to detect and observe in detail gravitational waves from astronomical sources.
• Tank of cleaning fluid:

Q14. Describe the difference between stellar parallax and stellar aberration. Why does the latter not interfere with measurements of the former when it results in a much larger angular displacement?

• On an interstellar scale, parallax created by the different orbital positions of the Earth causes nearby stars to appear to move relative to more distant stars. By observing parallax, measuring angles and using geometry, one can determine the distance to various objects. When the object in question is a star, the effect is known as stellar parallax.The stellar aberration is an astronomical phenomenon which produces an apparent motion of celestial objects about their real locations.Parallax is caused by a change in the position of the observer looking at a relatively nearby object, as measured against more distant objects, and is therefore dependent upon the distance between the observer and the object. In contrast, stellar aberration is independent of the distance of a celestial object from the observer, and depends only on the observer's instantaneous transverse velocity with respect to the incoming light beam, at the moment of observation.

20.What is the “mass function” of a binary star system and how is it determined?

• Using Kepler's third law we can conclude $f(M)={M_u}^3sin^3(i)/(M_s+M_u)^2=1.038\times10^{-7}V^3P$. For Mu is the invisible object, Ms is the visible object, P is the period((d), V is the observed velocity(km/s), i is the angle of inclination of the orbit.

25. Calculate the approximate distance to the heliopause. Does the local interstellar medium begin at this boundary? Explain

• The heliopause is the theoretical boundary where the Sun's solar wind is stopped by the interstellar medium; where the solar wind's strength is no longer great enough to push back the stellar winds of the surrounding stars.
• The Voyager 1 spacecraft passed termination shock in December 2004, when it was about 94 AU from the sun, byvirtue of the change in magnetic readings taken from the craft. In contrast, Voyager 2 began detecting returning particles when it was only 76 AU from the sun, in May 2006. This implies that the heliosphere may be irregularly shaped, bulging outwards in the sun's northern hemisphere and pushed inward in the south.

26. Discuss the observational status of searches for planets outside our own solar system.

27. What is the MHD approximation? What is the MHD equations for continuity, momentum conservation, and energy conservation.

• The simplest form of MHD, Ideal MHD, assumes that the fluid has so little resistivity that it can be treated as a perfect conductor.