Characteristics of Stars

Characteristics of Stars

• Stars appear as small pinpoints of light due to their great distance from Earth, but are comparable to the sun.
• A star is a massive ball of plasma that emits light.
• Stars vary based on brightness, color, surface temperature, size, and mass.

Brightness

• A star's brightness depends on its temperature, size, and proximity to Earth.
• Luminosity refers to the amount of light a star radiates determined by its size and surface temperature.
• Apparent magnitude is a star's brightness as seen from Earth.
• Absolute magnitude is the true, intrinsic brightness of a star.
• The larger the absolute magnitude number, the dimmer the star appears.
• First magnitude stars, or those with lower magnitude numbers (0, -1, etc.), are the brightest.

Surface Temperature and Colors

• Stars can be blue, white, yellow, orange, or red, with color indicating surface temperature.
• Astronomers use color as an indicator of a star's surface temperature.
• Hottest stars are blue-white with surface temperatures around 50,000°C.
• Coolest stars are red with surface temperatures around 3000°C.
• Zeta Eridani, Spica, and Algol are blue or blue-white stars with a surface temperature of 35,000°C.
• Sirius and Vega are white stars with a surface temperature of 10,000°C.
• The sun and Alpha Centauri A are yellow stars with a surface temperature of 6000°C.
• Alpha Centauri B is a red-orange star with a surface temperature of 5000°C.
• Proxima Centauri and Bernard's Star are red stars with a surface temperature of 3000°C.

Star Size

• Stars vary in size and can be smaller or thousands of times larger than the sun.
• Stars are classified into five types based on size: supergiant, giant, medium-sized, white dwarf, or neutron.

Masses of Stars

• Stars are primarily composed of the same elements.
• The composition of a star determines its mass.
• Hydrogen accounts for 60-80% of a star's mass.
• Helium accounts for 20-40% of a star's mass.
• Oxygen, neon, carbon, and nitrogen account for the other 4% of a star's mass.
• Stellar mass is measured relative to the sun, where the sun equals 1; for example, Rigel = 3.5.
• Stars of similar size can vary in mass due to differences in density.

Star Groups

• The Milky Way Galaxy is a large system of stars including the sun.
• The universe contains many galaxies with groups of stars, or clusters.
• Star clusters are categorized as globular or open clusters.
• Globular clusters are tightly packed, spherical groups containing hundreds of thousands of old stars, such as Omega Centauri.
• Open clusters are more loosely grouped with few hundred stars that are often young, such as the Pleiades.
• Stellar associations are moving groups due to gravitational disturbances disrupting open clusters.
• Star clusters may appear as a single faint star or cloud to the naked eye.
• Pleiades, Hyades, and the Beehive Cluster are star clusters visible without aid.

Constellations

• Constellations are patterns of stars named after figures, animals, gods, heroes, or objects.
• There are 88 recognized constellations.
• The Big Bear constellation includes the Big Dipper, which is visible in the northern sky.
• Pointers, two bright stars in the Big Dipper, point toward Polaris (North Star) located at the end of the Little Dipper's handle.
• Orion is a large constellation containing Betelgeuse and Rigel.
• Gemini, Canis Major, Canis Minor, Scorpius, Leo, and Virgo are other constellations.
• Stars served as a reference for early astronomers in measuring planetary motions and the sun.
• The apparent westward rotation of the celestial sphere is due to Earth’s eastward rotation.
• The ecliptic is the path of the sun, moon, and planets along the celestial sphere, tilted at 23.5 degrees to Earth's axis.
• The zodiac refers to the 12 constellations the sun passes through along the ecliptic, and faint stars serve as references for minute motions of nearby stars.
• Parallax measures distance by observing the apparent change in a star's position due to Earth's orbit.
• Constellations revolve around Polaris (North Star) in the Northern Sky.
• Ursa Major, Ursa Minor, and Draco appear to travel in an eternal circle around the pole due to their northern vicinity.

Constellations Visibility and Cultural Significance

• Constellation visibility varies throughout the year and by the observer's location on Earth.
• December nights are favorable for viewing winter constellations.
• PAGASA identifies celestial events like the Square of Pegasus.
• Some constellations are not visible from the North Pole.
• Philippine culture recognizes star groups like Balatik (Orion) and Moroporo.
• Balatik is a Filipino hunting trap equivalent.
• Ancient people used constellations for timing planting, fishing, and hunting.

Zodiac Constellations

• Constellation names are often Greek.
• The 12 zodiac constellations lie along the ecliptic and are still in use.
• The zodiac signs represent certain times of the year.

Zodiac Dates

• Aquarius: January 20 – February 18
• Pisces: February 19 – March 20
• Aries: March 21 – April 19
• Taurus: April 20 – May 20
• Gemini: May 21 – June 21
• Cancer: June 22 – July 22
• Leo: July 23 – August 22
• Virgo: August 23 – September 22
• Libra: September 23 – October 23
• Scorpio: October 24 – November 21
• Sagittarius: November 22 – December 21
• Capricorn: December 22 – January 19
• Ancient Greeks believed zodiac movements influenced human destiny.