Astronomy paper 1 topic 6

• The night sky


  Region of sky close to, and including, the constellation of Orion, the Hunter
• Orion


  • One of the exceptions where the pattern of stars bears a close resemblance to the name of the constellation
• Asterisms


  • The Plough (in Ursa Major)
  • Orion's Belt
  • The "W" (in Cassiopeia)
  • The Summer and Winter Triangles
• Asterisms


  • Unofficial, popular patterns of bright stars that do have a close likeness to their name
  • The stars in an asterism might belong to the same or different constellations
• Orion Nebula


  • A faint, rather fuzzy pink patch of light just below Orion's Belt
  • A stellar nursery of young stars, gas and dust
• Meteors/shooting stars


  • Appear for a split second as a bright streak of light caused by a dust particle, probably from the tail of a comet, burning up in the atmosphere
• Comets


  • Rare visitors to the inner Solar System
  • May be observed as an extended fuzzy object, possibly showing one or two tails, moving slowly against the background stars
• Supernovae


  • Appear as a bright new star, visible for possibly a few weeks and then slowly fade
• Planets


  • Do not appear to twinkle like stars
  • Slowly move eastwards from night to night through an imaginary narrow strip of sky called the Zodiacal Band
• Northern and Southern Lights (Aurora Borealis and Aurora Australis)


  • Spectacular astronomical phenomena of green, yellow and red curtains and whorls of light in the sky
  • Generally only able to be observed from polar regions, although have been seen on rare occasions from mid-UK latitudes
• Constellations and asterisms covered in the GCSE (9-1) Astronomy specification

  • Orion
  • Cassiopeia
  • Cygnus
  • Crux, the Southern Cross
  • The Summer Triangle asterism
• Stars in constellations


  • Can act as pointers to specific objects in the sky
• Pointers in Orion's Belt

  • Point downwards to the bright star Sirius and upwards to the bright red star Aldebaran and the Pleiades cluster
• Pointers in the Plough

  • Point out the bright star Arcturus and the pole star Polaris
• The Great Square of Pegasus


  • A good starting point for observing the Andromeda Galaxy, the most distant object that can be seen with the naked eye
• Artificial satellites


  • Appear as remarkably bright points of light in the twilight sky before fading from view as they enter the Earth's shadow
• Celestial sphere


  An imaginary sphere concentric with the Earth, used to map stars and other objects in the sky
• Equatorial coordinate system


  Used by amateur astronomers, with coordinates of declination (similar to latitude) and right ascension (similar to longitude)
• Horizontal coordinate system


  Used by amateur astronomers, with coordinates of azimuth (bearing from north) and altitude (angle above the horizon)
• Diurnal motion


  • Stars rise in the east, reach their highest point (culmination) and then set in the west, just like the Sun
• Circumpolar stars are those that never set below the horizon
• Naked-eye observing is possible from dark sky sites like the Galloway Forest Dark Sky Park
• Right ascension


  Coordinate used to locate celestial objects on the celestial sphere
• Right ascension lines are (almost) parallel to each other close to the celestial equator, but converge near the poles
• Since we are now 'inside the celestial sphere looking outwards to the sky, right ascension increases to the left
• Azimuth


  Bearing (measured in degrees) from due north, moving round eastwards to the point on the observer's horizon directly under the star
• Altitude


  Angle from the observer's horizon upward to the star
• Diurnal motion


  Stars rise in the east, reach their highest point (culminate) when they are due south as they cross the observer's meridian, and later set in the west
• Sidereal day


  Time it takes for the Earth to rotate through 360 degrees with respect to the stars, 23h 56min
• Solar day


  Time it takes for the Earth to rotate so that a given point on its surface is aligned with the Sun again, 24h 0min
• Local sidereal time (LST)


  The right ascension of a star that lies on the observer's meridian at a given moment in time
• Hour angle


  The time (in hours and minutes) since the object was last crossing the observer's meridian
• Hour angle


  Local sidereal time - right ascension
• Stars appear to revolve around the North Celestial Pole (NCP) in an anticlockwise sense, from west to east below Polaris, and east to west above Polaris
• Polar distance


  The angular distance of a star from the North or South Celestial Pole
• Declination


  The angular distance of a star north or south of the celestial equator
• Polar distance = 90 - declination
• Circumpolar stars


  Stars that do not set and remain visible all the time
• For a star to be circumpolar, its polar distance must be less than the latitude of the observer
• The best time to observe celestial objects is when close to culmination: they are highest in the sky and at their brightest