Astronomy Prologue
Lunar Eclipse
the blocking of sunlight to the moon🌝🌚🌕 that occurs when Earth is directly between the sun and the moon. - usually it's just a partial eclipse, and not a total one, which are rare (last no longer than 100 mins) - the Moon turns into an eerie, deep red, as the result of a small amount of sunlight being refracted (bent) by Earth's atmosphere onto the lunar surface, preventing the shadow from being completely black
The Zodiac
the classical band of 12 (modern 13) constellations that the Sun passes through during the year
The wobble of the Earth's axis causes what else to wobble?
the coordinate system, since they're based on Earth's axis, which means that the positions of the stars in that system change.
The Ecliptic
the path of the sun and the planets - it does not coincide with the Celestial Equator (it is inclined to the equator by 23.5 degrees)
Procession
the slow wobble of Earth's axis that makes the Celestial Pole and Equator move (the period of this wobble is about 26,000 years, which is why you don't notice it)
As a hypothesis stands up to experimentation, the hypothesis is likely to advance to acceptance as a ________
theory, which means that it is well-accepted and its predictions are correct
When something is so far aways as to be inaccessible, you have to use a distance measuring technique that involves
triangulation - "skinny" triangles - base is very small, and triangle is very long
After a day, Earth has returned to the same position with respect to a certain star, but the line of sight to the Sun has rotated by how much?
under just 1 degree (it takes about 4 extra mins to rotate the little extra angle)
Zero for Right Ascension is the
vernal equinox point
From night to night, the Moon moves from
west to east across the sky relative to the stars, or right to left, as viewed from the Northern Hemisphere
The Earth is moving around the Sun at
66,000 mph
Light Year
the distance light travels in one year, which is 6 trillion miles
Zero of Declination is the
Celestial Equator
If you extend Earth's axis into space, the points where it intersects are the...
Celestial Poles
The Earth is closest to the Sun in January and furthest from the Sun in July, so what is the real reason that it is hot here in the Summer?
The apparent size of the Sun changes with Earth's varying distance from it. The orientation of the Earth's axis (not perpendicular) 23.5 degrees away from perpendicular produces this effect.
If you watch the sky at night, you will observe stars:
rising in the East, moving across the sky and reaching max. altitude above the horizon in the South, then setting in the West
parallax of stars is measured in
seconds of arc (those angles are really small)
The detection limit is the
smallest value of something that a particular instrument can measure. - if you need to measure smaller values, you need a better instrument
During a lunar eclipse, if you were standing on the Moon, you would see a
solar eclipse, with the Earth blocking the Sun
The red coloration of a lunar eclipse is caused by:
sunlight deflected by Earth's atmosphere onto the Moon's surface.
What is the only natural object that orbits around the Earth?
the Moon sidereal period: 27.3 days synodic period: 29.5 days
The Moon changes its appearance in a regular cycle. One side of the Moon (and any other object as well) is dark because...
the Moon itself is in the way. The night side of the Moon is not in Earth's shadow.
The location of the Moon in the sky as se en from Earth, depends on
the Moon's location.
An Eclipse is when
the Sun, Earth, and Moon 🌙 line up precisely
What is an equator?
It is a plane that cuts the planet in 2 exactly through the center (halfway between poles) and perpendicular to the axis.
While Earth rotates once (24 hours), it moves at about
1,584,000 miles in its orbit
What 3 effects does the 23.5 degree Ecliptic tilt produce?
1. pole tipped away from the Sun gets COLD 2. altitude of the Sun is lower in Winter than in Summer 3. days are shorter in Winter than in Summer (all add up to seasonal changes)
1,000 in scientific notation =
10^3
Constellations
2-D projections of stars at very different distances - 88 in the celestial sphere
a star so far away that it has a parallax of 1 second of arc turns out to be
3.26 light years away - aka 1 parsec (parallax second)
The Celestial Sphere
An imaginary sphere surrounding Earth to which the stars are attached and randomly distributed
The average Earth-Sun distance is known as the
Astronomical Unit (AU) - another way of referring to the radius of Earth's orbit - the orbit diameter is therefore 2 AU
In the sky, the latitude equivalent is called
Declination - north declinations = (+) - south declinations = (-)
In a lunar eclipse, how does the Moon glow red if the sunlight is blocked by Earth?
Earth's atmosphere refracts some sunlight and bends it into the shadow. The blue light is blocked by the atmosphere, leaving the red light to go on to the Moon
What are Celestial (sky) coordinates based on?
Earth's axis as well
What determines the Sun's path among the stars?
Earth's orbit, since the apparent position of the Sun against the background stars depends on Earth's location. This scenario is called the Ecliptic.
What is the coordinate system centered on the Sun called?
Heliocentric coordinates
Occam's Razor
If you must chose between several explanations for something, simpler explanations are more likely to be true than complex ones. - the use of Occam's Razor would make the choice between the geocentric model and the Copernican model quite easy
Describe the phases of the Moon. 🌔🌓🌒🌑🌘🌗🌖🌕
New Moon 🌑: Moon is almost directly between the Sun and Earth (start of cycle), almost invisible. Appears to wax a little each night as a growing crescent 🌘. Quarter Moon: One week after New Moon, half of the lunar disk can be seen. A bit of the sunlit side of the moon shows on the right side. Gibbous Phase 🌖: during the next week, the Moon continues to wax (more than half of the lunar disk is visible) Full Moon 🌕: 2 weeks after New Moon, we see the entire face of the moon shining Reverse: The moon wanes (shrinks) and passes through the gibbous 🌔-->quarter 🌓--> crescent phases 🌒, and eventually becomes New Moon again.
Solar Eclipse
Occurs when the Moon passes directly between the Sun and Earth and casts a shadow over part of Earth - in a total solar eclipse, when the alignment is perfect, planets and some stars become visible in the daytime as the Sun's light is blocked. By pure chance the Sun and Moon have almost exactly the same angular size as seen from Earth—the Sun is much bigger than the Moon, but it also lies much farther away
What is a day?
One rotation of Earth with respect to 1. Solar Day: 1 rotation of planet relative to Sun 2. Sidereal Day: 1 rotation of planet relative to stars
A longer term effect of the Ecliptic tilt is...
Procession
In the sky, the longitude equivalent is called
Right Ascension (differs slightly from Earth's longitude though because it always measures eastward from the zero point)
In relation to the Equator, the Sun is
South the Equator for half the year, and North of it for the other half
What determines where the Celestial Poles and Celestial Equator are located?
The Earth
The star that does not move is _____ because it _______.
The North Star Polaris - because it is almost on the Earth's axis
Umbra
The darkest part of the moon's shadow, where the solar eclipse is seen in total - within the shadow, but outside the umbra is the prenumbra
The difference between Solar day and Sidereal day is that Sidereal day is
a little shorter (-3 mins 56 secs)
Because the Moon's orbit is slightly inclined the plane of the ecliptic, we do not see
a lunar eclipse at every full Moon
What is the Prime Meridian defined by?
a transit telescope at the old Royal Observatory in Greenwich, England - The Prime Meridian could actually be located anywhere; it's in London by international agreement
Scientific Method
a vaguely defined method for finding out things about the universe - weed out mistakes to avoid fooling yourself
How long does the complete cycle of lunar phases take to complete?
about 29 days
Annular Eclipse
an eclipse of the sun in which the edge of the sun remains visible as a bright ring around the moon. Half of solar eclipses are annular.
During a total solar eclipse, we can see the Sun's:
corona (the Sun's ghostly outer atmosphere)
The parsec system is based on the
diameter of Earth's orbit, because that is the longest baseline we can get
Since the Moon's orbit around Earth is not exactly circular, the Moon may be far enough from Earth at the moment of an eclipse that its:
disk fails to cover the disk of the Sun completely, even though its center coincide - in that case, there in no region of totality--the Umbra never reaches Earth at all, and a thin ring of sunlight can still be seen surrounding the Moon
The distance of an object and its parallax angle (formula)
distance = 1 / parallax
The ancients saw the sky as a
hollow sphere
A scientific hypothesis
is used to make a testable prediction which is then tested by means of some observation or experiment - if the experiment holds up, then you have support for the hypothesis
Triangulation
measure the shift (parallax) of object against a distant background
Latitude
measures angle north or south of the Equator (0 degrees)
Longitude
measures east or west from the zero (prime) meridian
As the Earth moves, the Sun appears to
move around the sky, so different constellations are visible at diff. times of year
