ASTR-1010 Lecture Notes - Lecture 4: Antarctic Circle, Solar Time, Hour Angle

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13 Sep 2016

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Chapter s2 celestial coordinates and motion in the sky. Celestial poles and equator correspond with earth"s poles and equator. Equinoxes and solstices are special points on the ecliptic. How to locate objects in the sphere each point corresponds to a location on the sphere. Right ascension longitude on the celestial sphere measured in hours east of the march equinox with the march equinox being 0 hours. Declination latitude on the celestial sphere measured in +/- degree above the celestial equator. Celestial coordinates of vega dec = +38 44" , ra = 18 h 35. 3 m. All objects with the same ra cross the meridian at the same time. Ra tells us how long after the march equinox we see the star/planet/celestial object. Sun"s declination negative in fall/winter and positive in spring/summer. Number of daylight hours varies by time of year: increase quickly in the spring, decreases quickly in the fall, stays nearly constant around the solstices.

Related Questions

Astronomy Parallax Lab

SCENARIO: Your lab group is planning an expedition to measure the distance to Mars by carefully measuring its position in the sky from two locations simultaneously when it is next at “opposition” (that is, when it is exactly opposite from the sun in the sky) on October 13, 2020. For the best, and most straightforward distance determination with the parallax method, Mars should be high in the sky (as near to your zenith as possible). This can be done by observing Mars: (a) from locations whose LATITUDES are similar to the DECLINATION of Mars at the date of measurement and (b) at the time of night when Mars is highest in the sky.

1a). Determine the Sky Coordinates of Mars on the date of opposition. The relevant coordinate is the Declination (RA/DE J2000 coordinates should be used) – this is the sky coordinate analogous to Latitude on the Earth’s surface. (Note, it is ok to determine these coordinates for Mars from anywhere on Earth for this initial measurement)

Mars DECLINATION on October 13, 2020: ___________________________

Your lab team needs to send observers to two cities that:

(a) have latitudes that are similar to the declination of Mars on that date (within 20 degrees); and

(b) have nearly the same longitude (that is, are nearly due North-South from each other (hint, you will need to go close to the equator!).

1b). Choose two of the cities below and use google maps, google earth or another online resource to record their names and Latitudes.

Melbourne, Australia	Kampala, Uganda	Tokyo, Japan
Omaha, NE, USA	Mumbai, Italy	Khartoum, Soudan

1c). At what time should you measure the sky coordinates (right ascension and declination) to get the most accurate possible parallax distance?

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ASTR-1010 Lecture Notes - Lecture 4: Antarctic Circle, Solar Time, Hour Angle

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