SpruceLake Elderhostel OBSERVING THE NIGHT SKY
June 1-6,1997 BiblicalSeminary
Climate
Normal monthlytemperature: 30-yr averages
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month
January
February
March
April
May
June
July
August
September
October
November
December
(From 1997 WorldAlmanac)
Sunrise/Sunset
Note: maxima andminima (bold) show earth's orbit not circular
date
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Jan 1
Jan 15
Feb 1
Feb 14
Mar 1
Mar 15
Apr 1
Apr 15
May 1
May 15
Jun 1
Jun 15
Jul 1
Jul 15
Aug 1
Aug 15
| Why is the sky blue in the daytime and black at night? Why is the sun red when it rises and sets?
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Sep 1
Sep 15
Oct 1
Oct 15
Nov 1
Nov 15
Dec 1
Dec 15
(From 1997 WorldAlmanac)
Horizon
| Can you see farther in the daytime or at night? How far can you see?
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Onan ideal smooth, spherical earth, our horizon is where a flat, broad conewith apex at our eye height tangentially touches the surface of theearth.
Ateye height approaching infinity, cone becomes a cylinder, so we can see onefull half of the earth; with earth's circumference c25 K mi, this meanshorizon is about 1/4 this distance, 6250 mi.
Onthe real earth, neither smooth not exactly spherical, horizon distance willvary in different directions due to details of relief and various obstacles(vegetation, buildings, etc.). If viewpoint is above local roughness, result is simpler, but will stilldepend on roughness near horizon in each direction.
Earth'sRotation
Earthrotates on its axis once in 24 hours. A complete rotation is 360o, so rotation rate is 360o/24hr = 15o/hr, which is 15o/hr/60 min/hr = 1/4 deg/min or 4min/deg.
Sincethe apparent diameter of both the sun and moon as viewed from the earth isabout 1/2 degree, the sun and moon appear to move across the sky at about aboutone diameter every two minutes.
Ifthe sun or moon sets vertically compared to the horizon, then (ignoring effectsof refraction by the atmosphere), the time of setting from when the lower edgefirst touches the horizon until the upper edge disappears would be about 2minutes.
Thesunset angle, however, varies with the season, since the earth's axis facestoward the sun in summer and away in winter. The angle of the earth's axis is about 23o27' or232deg. At the spring and fallequinoxes, the direction to the sun and the equator are aligned, so the sunsetangle (measured from the vertical) will be the same, or measured from thehorizontal, SS = 90 - lat.
ForPhila, this will be SS = 50o. The two extremes are the winter solstice and the summer solstice, whichare 232osmaller and larger than this.
MeasuringAngles
| Rules of Thumb Span 26o Palm 9o Thumb 2o
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So youroutstretched thumb marks off about 4 times the width of the sun or moon, aboutthe distance (at the equator) that the celestial sphere turns in 8minutes. You palm marks off thedistance it turns in about half an hour (actually 36 min).
Our Moon:
Moon:
The Planets:
Earth:
| Planet | a (AU) | Orbit. Period | Rot. Period | Mass* | Radius* | Density+ | Surface Gravity* | Known Moons |
| Mercury | 0.39 | 88d | 58.7d | .055 | .382 | 5.4 | .377 | 0 |
| Venus | 0.72 | 225d | 243d | .815 | .949 | 5.3 | .905 | 0 |
| Earth | 1.00 | 365d | 23.9h | 1.00 | 1.00 | 5.5 | 1.00 | 1 |
| Mars | 1.52 | 1.88y | 24.6h | .107 | .533 | 3.9 | .377 | 2 |
| Juptier | 5.20 | 11.9y | 9.92h | 318 | 11.2 | 1.3 | 2.54 | 16+ |
| Saturn | 9.54 | 29.5y | 10.7h | 95.2 | 9.45 | 0.7 | 1.07 | 19+ |
| Uranus | 19.2 | 84y | 17.3h | 14.5 | 4.10 | 1.2 | .869 | 15 |
| Neptune | 30.1 | 165y | 16.1h | 17.0 | 3.90 | 1.7 | 1.14 | 8 |
| Pluto | 39.4 | 248y | 6.4d | .003 | .18 | 2.0 | .07 | 1 |
Other Moons(Satellites):
| Planet | Moon | a (km) | period (days) | mass* | radius (km) |
| Earth | Moon | 385,000 | 27.3 | 1.00 | 1738 |
| Mars | Phobos | 9,380 | 0.319 | 1.3 [-7] | 12i |
| | Deimos | 23,500 | 1.26 | 2.7 [-8] | 7.5i |
| Jupiter | Io | 422,000 | 1.77 | 1.2 | 1816 |
| | Europa | 671,000 | 3.55 | 0.66 | 1569 |
| | Ganymede | 1,070,000 | 7.16 | 2.0 | 2631 |
| | Callisto | 1,883,000 | 16.7 | 1.5 | 2400 |
| Saturn | Mimas | 186,000 | 0.942 | .0005 | 197 |
| | Enceladus | 238,000 | 1.37 | .001 | 251 |
| | Tethys | 295,000 | 1.89 | .01 | 524 |
| | Dione | 377,000 | 2.74 | .014 | 560 |
| | Rhea | 527,000 | 4.52 | .034 | 765 |
| | Titan | 1,220,000 | 16.0 | 1.8 | 2575 |
| | Hyperion | 1,481,000 | 21.3 | ? | 135i |
| | Iapetus | 3,561,000 | 79.3 | .026 | 718 |
| | Phoebe | 12,950,000 | 550r | ? | 110 |
| Uranus | Miranda | 130,000 | 1.41 | .001 | 243 |
| | Ariel | 191,000 | 2.52 | .02 | 580 |
| | Umbriel | 266,000 | 4.14 | .02 | 600 |
| | Titania | 436,000 | 8.71 | .05 | 805 |
| | Oberon | 583,000 | 13.5 | .04 | 775 |
| Neptune | Triton | 354,600 | 5.88r | 0.8 | 1430 |
| | Nereid | 5,510,700 | 359 | 2 [-8] | 470 |
| Pluto | Charon | 19,700 | 6.39 | .02 | 600 |
A star is a hugeball of gas held together by its own gravity. Our sun is a star, by far the nearest one to us.
Because gravityis a spherically symmetric force, a star is spherical, except for a larger orsmaller bulge at its equator, depending on how fast it is spinning.
The force ofgravity heats up the gas inside the star, until it reaches a temperature highenough to turn on a nuclear reaction by which hydrogen is converted tohelium. Thereafter the starproduces light and heat from the energy produced by this reaction until thehydrogen in its core is exhausted. Stars getting their energy from hydrogen are called Main Sequence stars.
| Principal Stellar Classes of Stars | |||
| Type | Class | Surface Temp (deg K) | Example |
| Hottest, bluest | O | 40,000 | Alnitak (zeta Orionis) |
| Bluish | B | 18,000 | Spica (alpha Virginis) |
| Bluish-white | A | 10,000 | Sirius (alpha Can Maj) |
| White | F | 7,000 | Procyon (alpha Can Min) |
| Yellowish-white | G | 5,500 | Sun |
| Orangish | K | 4,000 | Arcturus (alpha Bootes) |
| Coolest, reddest | M | 3,000 | Antares (alpha Scorpii) |
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| The (17) Brightest Stars as Seen from Earth | |||||
| Star Name (Constellation) | Apparent Magnitude | Luminosity (cp sun) | Type | Radius (cp sun) | Distance (light yr) |
| Sun | -26.7 | 1.0 | Main seq | 1.0 | 0.0 |
| Sirius (Can Maj) | -1.4 | 23 | Main seq | 1.8 | 8.8 |
| Canopus (Carina) | -0.7 | (1400) | Supergiant | 30 | 110 |
| Arcturus (Bootes) | -0.1 | 115 | Red giant | (25) | 36 |
| Rigel Kent (Centaurus) | 0.0 | 1.5 | Main seq | 1.1 | 4.3 |
| Vega (Lyra) | 0.0 | (58) | Main seq | (3) | 27 |
| Capella (Auriga) | 0.1 | (90) | Red giant | 13 | 46 |
| Rigel (Orion) | 0.1 | (60,000) | Supergiant | (40) | (910) |
| Procyon (Can Min) | 0.4 | 6 | Main seq | 2.2 | 11 |
| Archernar (Eridanus) | 0.5 | (650) | Main seq | (7) | 120 |
| Hadar (Centaurus) | 0.7 | (10,000) | Supergiant | (10) | 490 |
| Betelgeuse (Orion) | 0.7 | 10,000 | Supergiant | 800 | 520 |
| Altair (Aquila) | 0.8 | (9) | Main seq | 1.5 | 16 |
| Aldebaran (Taurus) | 0.9 | 125 | Red giant | (40) | 68 |
| Acrux (So Cross) | 0.9 | (2500) | Main seq | (3) | (360) |
| Antares (Scorpius) | 0.9 | (9000) | Supergiant | (600) | (520) |
| Spica (Virgo) | 1.0 | (2300) | Main seq | 8 | 274 |
| Some Prominent Star Clusters | |||||
| | Name | Distance (ly) | Diameter (ly) | Mass (sun = 1) | Age (yr) |
| Open Clusters | Ursa Major | 68 | 23 | 300 | 200M |
| | Hyades | 137 | 16 | 300 | 500M |
| | Pleiades | 415 | 13 | 350 | 100M |
| | Beehive (M44) | 518 | 13 | 300 | 400M |
| Globular Clusters | M4 | 6500 | 30 | 150,000 | 1.4B |
| | M13 | 21500 | 35 | 660,000 | 1.4B |
| | M5 | 25000 | 40 | 850,000 | 1.4B |
| | M3 | 32500 | 42 | 1,100,000 | 1.4B |
A galaxy is amuch larger collection of stars than an open or even a globular cluster, whichare parts of galaxies. Galaxies were once called nebulae, then later, "islanduniverses."
Our galaxy hasbeen called "the Milky Way" since ancient times, long before we knewwhat it was. It is shaped ratherlike two fried eggs laid back-to-back, or a pair of marching-band cymbals, thatis, a rather flat disk of stars with a flattened-roundish bulge of stars in thecenter. It appears to be about100,000 ly across the disk, which is perhaps only 10,000 ly thick.
| Distances to Objects in the Milky Way Galaxy | |
| Destination | Distance (ly) |
| Nearest star beyond Sun | 4.2 |
| Sirius | 8.8 |
| Vega | 26 |
| Hyades cluster | 137 |
| Pleiades cluster | 415 |
| Central part of our spiral arm (Orion) | 1300 |
| Orion nebula | 1500 |
| Vertical distance to leave disk | 3300 |
| Next-nearest spiral arm (Sagittarius) | 3900 |
| Center of galaxy | 30,000 |
| M13 globular cluster | 36,000 |
| Far edge of galaxy | 78,000 |
| Types of Galaxies | ||||
| Name | Symbol | Shapes | Subclasses | Frequency |
| Elliptical | E | spherical to flat disk; both giant and dwarf | E0 -> E7+S0: less -> more flattened | giant 5% dwarf 50% |
| Spiral | S | disk w/ spiral arms | Sa -> Sc: smaller center, more open arms | 20% |
| Barred spiral | SB | bar connects center and arms | SBa -> SBc: same tendencies as regular spirals | |
| Irregular | Irr | no standard shape | none | 25% |
What is theuniverse? Is it "all that is,or ever was, or ever will be" (Carl Sagan)? We don't know. We could define it by Sagan's definition, but that might bemisleading. We're inside, anddon't know how big it is. Thevisible part apparently had a beginning at the big bang.
What we doknow:
1. Theuniverse is big. The distances to stars are measured in light years (6trillion miles each) or parsecs (3.26 ly). The distances to globular clusters in thousands oflight years (or kiloparsecs), to galaxies in millions of light years (ormegaparsecs), the distances to the most distant observable objects(galaxies and quasars) in billions of light years (or gigaparsecs).
2. The visibleuniverse cannot be both infinitely large and infinitely old.
3. The visibleuniverse is probably only some 10-20 billion years old.
a. The most distant objects we can see areonly about 10 billion ly away;
b. The age of the globular clusters is some10-15 billion years;
c. The expansion rate of the universe wouldsuggest that it was once very hot and compact some 10-20 billion years ago;
d. The age of the earth and sun is some 5billion years, and the sun does not appear to be a first generation star.
4. Theuniverse shows every evidence of being very carefully designed to be able tosupport life.
| The "Fine Tuned" Universe | ||
| Item | Consequences if larger | Consequences if smaller |
| Strong nuclear force constant | no hydrogen | nothing but hydrogen |
| Weak nuclear force constant | too much He; no heavy elements* | too little He; no heavy elements* |
| Gravitational force constant | stars too hot, burn too fast | stars too cool, no heavy elements |
| Electromagnetic force constant | insufficient chemical bonding | insufficient chemical bonding |
| Ratio of e-m to gravity | no stars less than 1.4 solar masses | no stars more than .8 solar masses |
| Ratio of electron to proton mass | insufficient chemical bonding | insufficient chemical bonding |
| Ratio of ## of protons to electrons | e-m dominates grav; no stars | e-m dominates grav; no stars |
| Expansion rate of universe | no galaxy formation | univ collapses quickly |
| Entropy level of universe | no proto-galaxy formation | no star formation |
| Mass density of universe | too much H-2, stars burn too fast | too little He & heavy elements |
| Velocity of light | stars too luminous | stars not luminous enough |
| Age of universe | no solar-type stars in right places | solar-type stars not yet formed |
| Initial uniformity of radiation | stars, clusters, galaxies not formed | universe mostly black holes |
| Fine structure constant | DNA doesn't work; stars too small | DNA doesn't work; stars too large |
| Average distance betw galaxies | insuff gas to continue star formation | sun's orbit too disturbed |
| Average distance betw stars | too few heavy elements for planets | planetary orbits unstable |
| Decay rate of proton | life exterminated by decay radiation | insuff matter for life |
| Energy level ratio C-12 to O-16 | insufficient oxygen | insufficient carbon |
| Ground state energy level of He-4 | insufficient O and C | insufficient O and C |
| Decay rate of Beryllium-8 | stars explode catastrophically | no elements heavier than Be |
| Mass excess: neutron over proton | n's decay, too few heavy elements | p's decay, stars collapse |
| Initial excess nucleons to anti-nuc | too much rad for planet formation | not enough matter for stars |
| Polarity of water molecule | heat of fusion, vap too gt for life | heats too small; ice won't float |
| Ratio of exotic to ordinary matter | univ collapse before solar-type stars | no galaxies formed |
5. Ourearth-sun environment appears to be unique and even designed.
1. galaxy type
too elliptical: star formation ends beforeenough heavy elements for life chemistry
too irregular: radiation exposure too high onoccasion, heavy elements for life chem not available
2. supernovaeruptions
too close: life on planet exterminated
too far: not enough heavy elements to formrocky planets
too frequent: life on planet exterminated
too infrequent: not enough heavy elements toform rocky planets
too soon: not enough heavy elements to formrocky planets
3. white dwarfbinaries
too few: insuff fluorine for life chemistry toproceed
too many: planetary orbits disrupted
too soon: not enough heavy elements to makefluorine
too late: flourine formed too late to beincorporated into planet
4. parent stardistance from center of galaxy
farther: heavy elements insuff for rockyplanets
closer: too much galactic radiation; planetaryorbits disturbed by large number of stars
5. number ofstars in planetary system
more than one: plantary orbits disrupted
less than one: not enough heat for life
6. parent starbirth date
more recent: star not yet in stable-burningphase; too many heavy elements
less recent: not enough heavy elements
7. parent starage
older: luminosity would change too quickly
younger: luminosity would change too quickly
8. parent starmass
greater: luminosity too variable; star burnstoo rapidly
less: life zone too narrow; tides slowrotation too much; uv radiation insufficient for photosynthesis
9. parent starcolor
redder: photosynthesis too weak
bluer: photosynthesis too weak
10. parent starluminosity change
increases too soon: runaway greenhouse effect
increases too late: runaway glaciation
11. planet'ssurface gravity
larger: atm retains too much ammonia, methane
smaller: atm loses too much water
12. planet'sdistance from parent star
further: too cool for stable water cycle
closer: too warm for stable water cycle
13. inclinationof planetary orbit
too great: temperature differences too extreme
14. eccentricityof planetary orbit
too great: seasonal temperature differencestoo extreme
15. axial tilt ofplanet
greater: surface temperature differences toogreat
less: surface temperature differences toogreat
16. rotationperiod of planet
longer: diurnal temperature differences toogreat
shorter: wind velocities too great
17. rate ofchange in rotation period
larger: surface temperature range necessaryfor life not sustained
smaller: surface temperature range necessaryfor life not sustained
18. age of planet
too young: planet would rotate too rapidly
too old: planet would rotate too slowly
19. magneticfield of planet
stronger: electromagnetic storms too severe
weaker: insuff protection for land life from hardradiation from sun and stars
20. thickness ofplanet's crust
thicker: too much oxygen lost to crust
thinner: too much volcanic & tectonicactivity
21. reflectivityof planet
greater: runaway glaciation
less: runaway greenhouse
22. collisionrate with asteriods and comets
greater: too many species wiped out
less: too few minerals needed for life incrust
23. ratio ofoxygen to nitrogen in atmosphere
larger: advanced life functions proceed tooquickly
smaller: advanced life functions proceed tooslowly
24. carbondioxide level in atmosphere
greater: runaway greenhouse effect
less: plant photosynthesis too low
25. water vaporlevel in atmosphere
greater: runaway greenhouse effect
less: too little rainfall for advanced landlife
26. atmosphericelectric discharge rate
greater: too much destruction from fire
less: too little nitrogen fixed in soil
27. ozone levelin atmosphere
greater: surface temperatures too low
less: surface temps too high; too much uv atsurface
28. quanity ofoxygen in atmosphere
greater: plants, hydrocarbons burn too easily
less: too little for advanced animals tobreathe
29. activity oftectonic plates
greater: too many life forms destroyed
less: nutrients lost by river runoff notrecycled
30. ratio ofoceans to continents
greater: diversity, complexity of life formslimited
smaller: diversity, complexity of life formslimited
31. globaldistribution of continents (for Earth)
too much in So hemisphere: seasonaltemperature differences would be too severe for advanced life
32. soilmineralization
too nutrient poor: diversity, complexity oflife forms limited
too nutrient rich: diversity, complexity oflife forms limited
33. gravitationalinteraction of planet with moon
greater: tidal effects on oceans, atmosphereand rotation period would be too severe
less: climatic instability; movement ofnutrients betw continents and oceans restricted; magnetic field too weak
Probability ofgetting all these in right range for a given planet is 1 in 10 to 53rd power!
Source: Ross, Creatorand Cosmos, 131-145.