Introduction Flashcards
Where do gamma rays and X-rays normally come from? Where do radio waves normally comes form?
Highly energetic places. Radio waves often come from cold areas.
Which EM waves can travel through the Earth’s atmosphere?
Optical and radio waves. X-Rays and ultraviolet rays cannot travel through , and infrared gets to ~ 20km above sea level.
How can we detect waves which can’t travel very far or at all through the atmosphere?
Have detectors which are high up or in space, away from the blocking atmosphere.
What are the three coordinates in the horizon system?
Azimuth (angle on Earth from North around, height above horizon (-90 to 90 degrees) and zenith (90 degrees - height: angles from the zenith to the position of the star).
What is a problem with the horizon system?
Stars continuously changing both coordinates due to Earth’s rotation and orbit around the Sun.
What are the two coordinates in the Equatorial system?
Right ascension (measured in h, m, s) and declination (measured from -90 degrees to 90 degrees)
What is a pro of the equatorial system?
Has a reference frame that is projected onto the celestial sphere, so a star will keep its coordinates even though the Earth is rotating.
What is the ecliptic and the equatorial plane?
Ecliptic is the plane of the orbit of the Sun & planets. The equatorial plane is the plane formed from projection of Earths equator, and since Earth is slightly tilted, is at an angle to the Ecliptic.
When do all the solstices and equinoxes happen?
- Winter solstice: -23.5 degree December 21st
- Autumnal equinox: 0 degrees September 23rd
- Summer solstice: 23.5 degrees June 21st
- Vernal equinox: 0 degrees March 20th
Why is the Earth being tilted to its orbital plane a problem?
Because the Sun and stars are in different positions in the sky over the year.
What happens in the precession of the celestial poles?
- Moon & Sun exercise a torque on the Earth rotation axis
- Rotation axis of moon precesses as well
What is the problem caused by the rotation axis of the Earth precessing?
Causes a variation in the positions of the poles.
What is the approximate distance of a galaxy?
8000pc
What are the two coordinates we measure galactically?
Galactic longitude and galactic latitude
What wavelengths are each pf the EM waves at?
- Gamma rays ~ 10^-9.5 cm and lower
- X-rays ~ 10^-9 to 10^-6 cm
- UV ~ 10^-6 to 10^-4.5cm
- Infrared ~ 10^-4 to 10^-2.5cm
- Radio & microwaves ~ 10^-4 and above cm
