AST101H1 Lecture : chapter 3

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sangriareindeer116

16 Feb 2011

School

UTSG

Department

Astronomy & Astrophysics

Course

AST101H1

Professor

Clifford Orwin

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AST101H1 Full Course Notes

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Modern measures of time come from ancient observation of motion in the sky. Length of the day is the time it takes the sun to make one full circuit in the sky. Length of a month comes from the moons cycle of phases. Length of year comes from the seasons. Ancient people could estimate the time from the position and phase of the moon. Positions of the stars can also indicate the tim, as long as u know the date. Egyptians divided the daylight into 12 equal parts. A. m and p. m - latin terms ante meridiem and post meridiem (before the middle of the day and after the middle of the day) The names of the seven days of the week are based on: The seven naked-eye objects that appear to move among the constellations. Daylight summer hours were longer (1/12 of the daylight lasts longer) than the daylight winter hours.

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Introduction. Telescope time is a valuablecommodity in astronomy, so astronomers plan their observationscarefully. One of the first steps is to choose what type ofobservation to make. Recall that three basic types of astronomicalobservation are imaging (taking a photograph of anobject), spectroscopy (spreading an object's light into aspectrum), and timing (measuring how an object's lightvaries with time).

Part A: Sort each of the astronomical questionsbelow into the appropriate bin based on the type of observation youwould need to perform to answer it.

Three Categories: Imagine, Spectroscopy andTiming

The Questions:

1. "What are the major surface features of Mars?"

2. "What is the temperature of Jupiter's atmosphere?"

3. "Does the star Mira vary in brightness?"

4. "How large is the Andromeda Galaxy?"

5. "What is the chemical composition of the Crab Nebula?"

6. "Is the X-ray emission fro the galactic center steady orchanging?"

7. "Is the star Vega moving toward us or away from us?"

8. "Are stars in the Orion Nebula surrounded by dusty disks ofgas?"

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Introduction: Different telescopes areoptimized for observing different wavelengths of light, so anotherconsideration in planning an observation is deciding what type oftelescope to use.

Part B: Each of the following statementsdescribes an astronomical measurement. Place each measurement intothe appropriate bin based on the type of telescope you would use tomake it.

Three Categories: Infrared Telescope, VisibleLight Telescope and X-Ray Telescope

The Statements:

1. Study a dense cloud of cold gas in space.

2. Measure the brightness of a star that is similar to ourSun.

3. Observe the hot (1-million K) gas in the Sun's corona.

4. Obtain a spectrum of sunlight reflected by Mars.

5. Determine the surface temperature of Venus.

6. Look for high-energy radiation from a supernova.

Thank you so much to whoever helps!

1. A transformer for an answering machine takes an ACvoltageof 170 V. (maximum, or peak-to-peak) as its input andprovides 7.8V (rms) as its output to the answering machine.

A) What is the rms equivalent to thispeak-to-peakvoltage?

B) Calculate the turns ratio between the primaryandsecondary.

C) When not answering, the machine uses a maximum power of5.0W. What is the current (rms) drawn from the 170 V line?

2. An astronomer is making an observation of anew-discoveredgalactic object. Part of this observation is theanalsis of thelight emitted by the object. It is observed that thislightincludes a clear pattern of the emission spectrum ofatomichydrogen.

Part of that spectrum is the HÎ± line, which on earth hasawavelength of 656.258 nm

(10^-9m). The observed light from this objecthasthis spectral line measured at 659.0 nm.

Explain this discrepancy, quantitatively, using theDopplerEffect.

thank you. Please help me.

Pulsars are neutron stars that emit X rays and other radiation insuch a way that we on Earth receive pulses of radiation from thepulsars at regular intervals equal to the period that they rotate.Some of these pulsars rotate with periods as short as 1 ms! TheCrab Pulsar, located inside the Crab Nebula in the constellationOrion, has a period currently of length 33.085 ms. It is estimatedto have an equatorial radius of 15 km, an average radius for aneutron star.
(a) What is the value of the centripetal acceleration of an objecton the surface at the equator of the pulsar?
1 m/s2

(b) Many pulsars are observed to have periods that lengthenslightly with time, a phenomenon called "spin down." The rate ofslowing of the Crab Pulsar is 3.50 10-13 s per second, whichimplies that if this rate remains constant, the Crab Pulsar willstop spinning in 9.50 1010 s (about 3000 years from today). What isthe tangential acceleration of an object on the equator of thisneutron star?

AST101H1 Lecture : chapter 3

AST101H1 Full Course Notes

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