UPCAT General Science (Extended) — Astronomy & the PlanetsCheat Sheet
Astronomy & the Planets cheat sheet for UPCAT aspirants. If you could only take one sheet of paper into your review session, this is what it would look like. University of the Philippines's most-tested concepts, all in one place.
Exam context
On the UPCAT 2026, the General Science (Extended) subtest carries a "Extended coverage for UP Science programs" weight in University of the Philippines's pattern. Astronomy & the Planets lands at position 5th out of 6 in the standard review order. Target score is UPG ≤ 2.2 typical, and roughly 20 items come from General Science (Extended) on a typical UPCAT paper.
Astronomy & the Planets - Cheat sheet
Your last-minute revision companion for Astronomy & the Planets - everything you need for exam success in 30 minutes
Sections
Formulas
Formula
Kepler's 3rd Law: T² ∝ r³
Meaning
T = orbital period, r = average distance from sun
Watch Out
Period squared, not period itself - common mistake in calculations
When To Use
When comparing planetary orbital periods and distances
Common Values
Value
240,000 miles
Symbol
d
Quantity
Earth-Moon distance
Value
27.3 days
Symbol
T
Quantity
Moon's orbital period
Value
29.5 days
Symbol
-
Quantity
Lunar month
Section Title
Celestial Bodies & Classifications
Important Facts
- Blue planets (Earth, Neptune, Uranus) are blue due to atmospheric gases
- More than 5,000 asteroids discovered, most between Mars and Jupiter
- Comets have tails that point away from the Sun due to solar wind
- Meteors burn up in Earth's atmosphere creating 'shooting stars'
Key Definitions
Term
Astronomy
Example
Study of stars, planets, galaxies, and space phenomena
Definition
Scientific study of celestial bodies and everything outside Earth's atmosphere
Term
Satellite (Moon)
Example
Earth's Moon, Jupiter's 67 moons
Definition
A body orbiting around a planet
Term
Orbit
Example
Earth's elliptical path around the Sun
Definition
The path traveled by a body in space
Term
Asteroids
Example
Over 5,000 discovered, mostly between Mars and Jupiter
Definition
Small rocky bodies orbiting the Sun, also called minor planets
Term
Comets
Example
Halley's Comet with its visible tail
Definition
Frozen dust and gases with icy centers, described as 'dirty snowballs'
Term
Meteors
Example
Shooting stars visible in night sky
Definition
Fragments of comets, planets, moons, or asteroids that have broken off
Diagrams To Know
- Solar system structure with planetary positions
- Comet structure showing nucleus, coma, and tail
- Asteroid belt location between Mars and Jupiter
Common Values
Value
>37,000°F
Symbol
T
Quantity
Blue star temperature
Value
~10,000°F
Symbol
T
Quantity
Yellow star temperature
Value
<5,500°F
Symbol
T
Quantity
Red star temperature
Section Title
Stars & Stellar Evolution
Important Facts
- Star color indicates temperature: Blue (hottest) → Yellow → Red (coolest)
- Brown dwarfs are called 'failed stars'
- Pulsar = Pulsating star (shortened version)
- White dwarfs are final stage of Sun-sized stars
- Black holes have escape velocity greater than speed of light
Key Definitions
Term
Blue Stars
Example
Rigel, Spica - appear blue-white in color
Definition
Hottest stars with surface temperature over 37,000°F
Term
Yellow Stars
Example
Our Sun - appears yellow from Earth
Definition
Warm stars like the Sun with temperature around 10,000°F
Term
Red Stars
Example
Betelgeuse - appears reddish in color
Definition
Coolest stars with surface temperature less than 5,500°F
Term
White Dwarfs
Example
Final stage of Sun-like stars after fuel depletion
Definition
Stars that ran out of energy and collapsed due to gravity
Term
Brown Dwarfs
Example
Objects between largest planets and smallest stars
Definition
Failed stars - too massive for planets but lack energy to be true stars
Term
Supernova
Example
Massive star explosion visible across galaxies
Definition
Extremely large exploding star at end of life cycle
Term
Neutron Stars
Example
Incredibly dense - teaspoon weighs billions of tons
Definition
Dense remnants formed after a supernova explodes and shrinks
Term
Pulsars
Example
Lighthouse effect - beams sweep across space
Definition
Rapidly spinning neutron stars emitting regular radio wave bursts
Term
Black Hole
Example
Gravity so strong that light cannot escape
Definition
Created by total gravitational collapse of massive star or star group
Diagrams To Know
- Stellar evolution sequence from main sequence to final stage
- H-R diagram showing star types by temperature and luminosity
- Pulsar beam rotation diagram
Reactions Or Equations
Note
Powers all main sequence stars including our Sun
Equation
Nuclear Fusion: 4H → He + energy
Conditions
Extreme temperature and pressure in stellar cores
Section Title
The Sun's Structure
Important Facts
- Sun has three main regions: interior, visible surface, atmosphere
- Nuclear fusion in core powers the Sun
- Energy from core takes thousands of years to reach surface
- Corona is paradoxically hotter than the photosphere
- Solar wind originates from outer corona
- Sunspots are cooler regions caused by magnetic fields
Key Definitions
Term
Core
Example
Temperature reaches 15 million°C
Definition
Center and hottest region where nuclear fusion occurs
Term
Radiative Zone
Example
Energy takes thousands of years to travel through this layer
Definition
Region where energy travels outward by photons and thermal radiation
Term
Convection Zone
Example
Hot plasma rises, cool plasma sinks
Definition
Outer layer where heat moves upward through convection
Term
Photosphere
Example
What we see as the Sun's surface from Earth
Definition
Sun's visible surface boundary between interior and atmosphere
Term
Sunspots
Example
Appear darker because they're cooler than surrounding areas
Definition
Temporary dark areas on photosphere caused by magnetic field flux
Term
Chromosphere
Example
Visible as red ring during total solar eclipse
Definition
Lower solar atmosphere region that appears bright red during eclipse
Term
Corona
Example
Visible as white halo during total solar eclipse
Definition
Upper solar atmosphere hotter than photosphere, source of solar wind
Diagrams To Know
- Cross-section of Sun showing all layers from core to corona
- Solar eclipse diagram showing corona visibility
- Convection currents in convection zone
Common Values
Value
11.9 years
Symbol
T
Quantity
Jupiter orbital period
Value
29.5 years
Symbol
T
Quantity
Saturn orbital period
Value
58.6 Earth days
Symbol
d
Quantity
Mercury day length
Section Title
Planetary Data & Characteristics
Important Facts
- Mercury has no moons and no rings
- Venus rotates backwards (retrograde rotation)
- Earth is the only known planet with life
- Mars has 2 moons: Phobos and Deimos
- Jupiter has 67 known moons, largest planet
- Saturn has lowest density (0.70 g/cm³), would float in water
- Uranus rotates on its side (97.9° axis tilt)
- Neptune is the windiest planet
- Pluto is now classified as dwarf planet
Key Definitions
Term
AU (Astronomical Unit)
Example
Earth is 1.00 AU from Sun, Jupiter is 5.20 AU
Definition
Average distance from Earth to Sun, used to measure planetary distances
Term
Terrestrial Planets
Example
Made of rocks and metals, relatively small
Definition
Rocky planets: Mercury, Venus, Earth, Mars
Term
Gas Giants
Example
Much larger than terrestrial planets, have ring systems
Definition
Large planets made of hydrogen and helium: Jupiter, Saturn
Term
Ice Giants
Example
Contain water, methane, and ammonia ices
Definition
Uranus and Neptune - made of hydrogen compounds
Diagrams To Know
- Solar system scale showing relative sizes and distances
- Planet classification chart (terrestrial vs gas giants)
- Planetary orbital periods vs distance graph
Formulas
Formula
Moon gravity = 1/6 × Earth gravity
Meaning
Objects weigh 6 times less on Moon than Earth
Watch Out
This affects weight, not mass - mass stays the same
When To Use
Calculating weight or gravitational effects on Moon
Common Values
Value
1/4 of Earth
Symbol
d
Quantity
Moon diameter ratio
Value
1/81 of Earth
Symbol
m
Quantity
Moon mass ratio
Value
1/6 of Earth
Symbol
g
Quantity
Moon gravity ratio
Section Title
Moon Phases & Properties
Important Facts
- Moon diameter = 1/4 of Earth's diameter
- Moon volume = 1/50 of Earth's volume
- Moon mass = 1/81 of Earth's mass
- Moon gravity = 1/6 of Earth's gravity
- Revolution period = Rotation period = 27.3 days (synchronous rotation)
- Lunar month = 29.5 days (phase cycle)
- Moon orbits at 240,000 miles from Earth
- Moon travels at 2,300 mph in orbit
Key Definitions
Term
New Moon
Example
Starting phase of lunar cycle
Definition
Moon between Earth and Sun, not visible from Earth
Term
Waxing Crescent
Example
Growing from new moon toward first quarter
Definition
Increasing illumination, less than half visible
Term
First Quarter
Example
90° from Sun-Earth line
Definition
Half of Moon visible from Earth, right side illuminated
Term
Waxing Gibbous
Example
Growing toward full moon
Definition
More than half but less than full Moon visible
Term
Full Moon
Example
Earth between Sun and Moon
Definition
Entire Moon face visible from Earth
Diagrams To Know
- Eight phases of Moon cycle diagram
- Moon-Earth-Sun alignment for each phase
- Tidal effects diagram showing Moon's gravitational influence
Section Title
Historical Models & Laws
Important Facts
- Ptolemy developed geocentric (Earth-centered) model
- Copernicus proposed heliocentric (Sun-centered) model in 1543
- Kepler discovered elliptical orbits, not circular
- Galileo used telescope to support heliocentric model
- Newton's gravity theory explained elliptical orbits
Key Definitions
Term
Geocentric Model
Example
Ancient belief system before Copernicus
Definition
Ptolemy's model with Earth at center, everything revolving around it
Term
Heliocentric Model
Example
Revolutionary idea that challenged geocentric view
Definition
Copernicus's model with Sun at center, planets revolving around it
Term
Elliptical Orbits
Example
More accurate description than circular orbits
Definition
Kepler's discovery that planets move in oval paths, not circles
Diagrams To Know
- Geocentric vs heliocentric model comparison
- Elliptical orbit diagram showing foci
- Kepler's second law area sweep diagram
Reactions Or Equations
Note
Not perfect circles as previously thought
Equation
Kepler's 1st Law: Planets orbit in ellipses
Conditions
Sun at one focus of ellipse
Note
Explains varying orbital speeds
Equation
Kepler's 2nd Law: Closer to Sun = faster movement
Conditions
Equal areas swept in equal time
Note
Links orbital period to distance from Sun
Equation
Kepler's 3rd Law: T² ∝ r³
Conditions
For any planet around the Sun
Common Values
Value
4.5 billion years
Symbol
t
Quantity
Solar system age
Section Title
Eclipses & Solar System Formation
Important Facts
- Solar eclipse occurs during new moon phase
- Lunar eclipse occurs during full moon phase
- Solar system formed approximately 4.5 billion years ago
- Nebular theory explains formation from dust and gas cloud
- All major solar system objects formed around same time
Key Definitions
Term
Solar Eclipse
Example
Moon's shadow falls on Earth during daytime
Definition
Moon passes between Earth and Sun, blocking Sun's view
Term
Lunar Eclipse
Example
Moon appears red during total lunar eclipse
Definition
Earth passes between Sun and Moon, Earth's shadow on Moon
Term
Nebular Theory
Example
Explains formation of Sun, planets, moons, and asteroids
Definition
Solar system formed from nebula cloud of dust and gas 4.5 billion years ago
Diagrams To Know
- Solar eclipse geometry showing Moon's shadow on Earth
- Lunar eclipse geometry showing Earth's shadow on Moon
- Nebular theory formation sequence diagram
Must Remember
- Kepler's 3 Laws: (1) Elliptical orbits, (2) Closer = faster, (3) T² ∝ r³
- Star temperature order: Blue (hottest) > Yellow > Red (coolest)
- Moon gravity = 1/6 Earth gravity, diameter = 1/4 Earth diameter
- Terrestrial planets: Mercury, Venus, Earth, Mars (rocky)
- Gas giants: Jupiter, Saturn (H, He); Ice giants: Uranus, Neptune
- Solar eclipse = Moon blocks Sun; Lunar eclipse = Earth blocks sunlight to Moon
- Sun structure: Core (fusion) → Radiative → Convection → Photosphere → Chromosphere → Corona
- Nebular theory: Solar system formed 4.5 billion years ago from dust/gas cloud
- Asteroid belt located between Mars and Jupiter
- Copernicus = heliocentric model; Ptolemy = geocentric model
Last Minute Tips
- Remember planet order using 'My Very Educated Mother Just Served Us Nachos' (including Pluto as dwarf planet)
- For Kepler's laws: Think 'EAR' - Elliptical, Area (equal areas), Ratio (T² ∝ r³)
- Eclipse memory trick: SOLar eclipse = Sun Obscured by moon Looking from earth; LUNar = LUmiNation blocked from moon
- Star colors match flame colors: Blue flame hottest, red flame coolest
- Moon phases: NEW-WAX-FIRST-WAX-FULL-WANE-THIRD-WANE cycle (8 phases total)
Comparison Tables
Rows
Values
- Mercury, Venus, Earth, Mars
- Jupiter, Saturn
Property
Examples
Values
- Rocks and metals
- Hydrogen and helium
Property
Composition
Values
- Small
- Large
Property
Size
Values
- High (3-6 g/cm³)
- Low (0.7-1.3 g/cm³)
Property
Density
Values
- Few or none
- Many moons
Property
Moons
Values
- None
- Ring systems present
Property
Rings
Columns
- Property
- Terrestrial
- Gas Giants
Table Title
Terrestrial vs Gas Giant Planets
Rows
Values
- >37,000°F
- Blue-white
- Rigel, Spica
Property
Blue Stars
Values
- ~10,000°F
- Yellow
- Sun, Capella
Property
Yellow Stars
Values
- <5,500°F
- Red
- Betelgeuse, Antares
Property
Red Stars
Columns
- Star Type
- Temperature
- Color
- Examples
Table Title
Star Types by Temperature
Rows
Values
- New Moon
- Full Moon
Property
Moon Phase
Values
- Moon between Sun-Earth
- Earth between Sun-Moon
Property
Alignment
Values
- Moon's shadow on Earth
- Earth's shadow on Moon
Property
Shadow Location
Values
- Narrow path on Earth
- Entire night side of Earth
Property
Visibility
Values
- Few minutes
- Few hours
Property
Duration
Values
- Never look directly
- Safe to observe
Property
Safety
Columns
- Property
- Solar Eclipse
- Lunar Eclipse
Table Title
Solar Eclipse vs Lunar Eclipse
Previous chapter
Atmosphere, Weather & Climate
Next chapter
Ecology, Biogeochemical Cycles & Species Relationships
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