Department

AstronomyCourse Code

ASTA01H3Professor

Parandis TajbakhshStudy Guide

MidtermThis

**preview**shows pages 1-2. to view the full**6 pages of the document.**ASTRONOMY MIDTERM REVIEW

LECTURE #1

-Scientific notation

-Tkelvin = Tcelsius + 273

-Astronomical measurements

o1 AU = 150, 000, 000 km

o1 ly = 63, 000 AU

Distance = speed x time

-Speed of light: 3x108 m/s

oExample. Convert 642ly into astronomical units.

642(63, 000) = 4.0x107 AU

oExample. How long does it take to get from sun to Jupiter if distance is 7.4x108 km?

t = [7.4x1011 m / 3x108 m/s] / 60

= ~40 mins

LECTURE #2

-Apparent Magnitude: the apparent brightness of a star as observed from Earth

oObserved apparent brightness depends on intrinsic brightness and distance

-Brightness

oMagnitude 1 (brightest) -------------- Magnitude 6 (faintest)

-Flux

F1/F2 = 2.5(m2-m1)

oExample. Star 1 m1= -1.5 while star 2 m2= 8. Which is brighter?

F1/F2 = 2.5(8- (-1.5))

= 39 Star 2 is 39 times brighter than star 1

LECTURE #3

-Celestial sphere

oZenith is the point right above you

oNadir is the point right below you

oNCP/SCP are points where the extension of earth’s axis pierces through the celestial sphere

oCelestial equator is an extension of the earth’s equator on the celestial sphere

oHorizon of each observer is the plane of the circle with the largest circumference perpendicular to line of

zenith-nadir of observer

oCelestial meridian is the circle that passes through zenith, nadir, NCP/SCP

Intersection of celestial meridian and horizon defines N and S

Intersection of celestial equator and horizon defines E and W

oElevation of daily path which is parallel to the celestial equator is known as declination (δ)

- OBSERVER DEPENDENT -

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LECTURE #4

-Star rises when it comes above the horizon and sets when it’s below it

-If declination of a star is larger than 90 – latitude (θ), then that star never sets and always remains above the

horizon = CIRCUMPOLAR STAR

oExample. If Toronto’s altitude is 43.7°N, θ = 43.7

90 – 43.7 = 46.3°N

so any star 46.3°N of NCP is a circumpolar star

oExample. From Toronto, which of the following is a circumpolar star:

Sirius θ = -16°N

Betelgeus θ = 7°N

Polaris θ = 89°N

Proximas θ = -62°N

-Precession is the slow movement of the axis of a spinning body around another axis due to a torque (such as

gravitational influence) acting to change the direction of the first axis

-Ecliptic is when the sun orbits the earth which occurs once a year in a CCW motion (WE)

oSun moves on its annual path by less than 1° a day

oPlane of ecliptic is titled with respect to celestial equator

Angle between the two is OBLIQUITY OF ECLIPTIC

oIntersection of ecliptic and celestial equator is Vernal Equinox/Autumnal Equinox

At which point, declination is 0°

-Solstice is point of maximum/minimum declination

oSummer Solstice in northern hemisphere

Sun spends LONG time above horizon; rises in NE and sets in NW

oWinter Solstice in norther hemisphere

Sun spends LITTLE time above horizon; rises in SE and sets in SW

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