lecture stars and constellations

7/29/2019 Lecture Stars and Constellations

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Stars


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Star names come from Greek, Latin

and Arabic origins. For example,Sirius and Capella are of Greek and

Latin origns and Vega, Rigel,

Aldebaran are Arabic derivations. In some cases two names are given

to a star because some stars are

refered to with multiple names.


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Rigel

Alnilam

Alnitak

Mintakal

BellatrixBetelguese

Saiph


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Arabic names and translations

StarArabic name Translation

Betelgeuse (in Orion) Yad al Jawaz the hand of the twin

Mintaka (in Orion) Al Mintaqah the belt

Alnilam (in Orion) Al Nidham the string of pearls

Saiph (in Orion) Al Saif the swordAlgorab (in Corvus) Al Ghurab the raven

Alpheratz (in Pegasus) Surat al Faras the navel of the horse

Kaus (in Sagittarius) Al Qaus the bow

Vega (in Lyra) Al Waqi' the stooping eagleAldebaran (in Taurus) Al Dabaran the follower

Fomalhaut (in Pisces) Fam al Hut the mouth of the fish

Lesath (in Scorpio) Al Las'ah the sting

Rastaban (in Draco) Ra's al Thu'ban the head of the snake


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Star Brightness

Magnitude

apparent

absolute
http://www.stargazing.net/david/constel/constel/canismajor.html


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Apparent Magnitude

The apparent magnitudeof an object isthe "what you see is what you get"magnitude. It is determined using the

apparent brightness as observed, with no

consideration given to how distance is

influencing the observation.

However, the apparent magnitude is not so

useful because it mixes up the intrinsicbrightness of the star (which is related to its

internal energy production) and the effect of

distance (which has nothing to do with the

intrinsic structure of the star).


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Apparent Visual Magnitudes

Object Apparent VisualMagnitude

Sirius (brightest star) -1.5

Venus (at brightest) -4.4

Full Moon -12.6

The Sun -26.8

Faintest naked eye stars 6-7

Faintest star visible fromEarth telescopes

~25

Faintest star visible fromHubble Space Telescope

~?


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Absolute Magnitude

Astronomers define the absolute

magnitudeto be the apparent magnitudethat a star would have if it were (in our

imagination) placed at a distance of 10parsecs (which is 32.6 light years) from

the Earth.


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Apparent and absolute magnitudes of common stars

ObjectApparent

Magnitude(mV)

AbsoluteMagnitud

e (MV)

Sun -26.8 4.83

Sirius -1.47 1.41

Vega 0.04 0.5

Betelgeuse 0.41 -5.6

Polaris 1.99 -3.2

Magnitudes from Seeds (1997) and Burnham (1978).

Which is the brightest

star?


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Light Year

A light-year is equal to:

exactly 9,460,730,472,580.8 km (about

10 Pm)

about 5,878,630,000,000 international

miles

about 63,241.1 astronomical units about 0.306601 parsecs
http://en.wikipedia.org/wiki/Kilometrehttp://en.wikipedia.org/wiki/Petametrehttp://en.wikipedia.org/wiki/Milehttp://en.wikipedia.org/wiki/Milehttp://en.wikipedia.org/wiki/Astronomical_unithttp://en.wikipedia.org/wiki/Parsechttp://en.wikipedia.org/wiki/Parsechttp://en.wikipedia.org/wiki/Astronomical_unithttp://en.wikipedia.org/wiki/Milehttp://en.wikipedia.org/wiki/Milehttp://en.wikipedia.org/wiki/Petametrehttp://en.wikipedia.org/wiki/Kilometre


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The Milky Way is about 100,000 light-

years across.

The nearest known star(other than the

Sun), Proxima Centauri, is about 4.22

light-years away

Reflected sunlight from the Moon's surface

takes 1.2-1.3 seconds to travel the

distance to the Earth's surface.
http://en.wikipedia.org/wiki/Milky_Wayhttp://en.wikipedia.org/wiki/Starhttp://en.wikipedia.org/wiki/Proxima_Centaurihttp://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Proxima_Centaurihttp://en.wikipedia.org/wiki/Starhttp://en.wikipedia.org/wiki/Milky_Way


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Astronomical Unit

Astronomical Unit - 1 AU = approximately

150 million kilometers (93 million miles)


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The Earth is 1.00 0.02 AU from the Sun.

The Moon is 0.0026 0.0001 AU from the Earth.

Mars is 1.52 0.14 AU from the Sun.

Jupiteris 5.20 0.05 AU from the Sun. Pluto is 39.5 9.8 AU from the Sun.

Proxima Centauri (the nearest starto Earth,excluding our own Sun) is ~268 000 AU awayfrom the Sun.

The mean diameter ofBetelgeuse is 2.57 AU.

The distance from the Sun to the centre of theMilky Way is approximately 1.7109 AU.
http://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Marshttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Plutohttp://en.wikipedia.org/wiki/Proxima_Centaurihttp://en.wikipedia.org/wiki/Starhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Betelgeusehttp://en.wikipedia.org/wiki/Milky_Wayhttp://en.wikipedia.org/wiki/Milky_Wayhttp://en.wikipedia.org/wiki/Betelgeusehttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Starhttp://en.wikipedia.org/wiki/Proxima_Centaurihttp://en.wikipedia.org/wiki/Plutohttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Marshttp://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Earth


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Location celestial objects


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Azimuth


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Altitude


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Celestrial Coordinate System


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Celestial coordinate system

the North and South Celestial Poles aredetermined by projecting the rotation axis ofthe Earth to intersect the celestial sphere,

which in turn defines a Celestial Equator. The celestial equivalent of latitude is called

declination(measured in degrees North (positive numbers) or South (negativenumbers) of the Celestial Equator).

The celestial equivalent of longitude is calledright ascension(measured in degrees, 15 degrees every hour).


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Reference

McNish, L. (2007). RASC Calgary Centre - A Complete Guide to Right Ascension andDeclination. retrieved on 31 Dec 2008 from http://calgary.rasc.ca/radecl.htm

Discovering the Sky Chapter 1. Retrieved from

http://oz.plymouth.edu/~sci_ed/Turski/Courses/Astronomy/Notes/Chap.1.NightSky.html
http://calgary.rasc.ca/radecl.htmhttp://calgary.rasc.ca/radecl.htm


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Constellation


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Where are they in the sky?


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How do you know them?


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Star Chart


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How to become an astronomer

lecture stars and constellations

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