91Ó°ÊÓ

An observatory's position on Earth is described by its latitude and longitude. The latitude determines how far north or south the observatory is from the equator. It is expressed in degrees, with the equator at 0° latitude. In our exercise, we have an observatory located at 45° N, which means it is 45° north of the equator.
Longitude, meanwhile, specifies the east-west position. It is measured from the Prime Meridian, which is at 0° longitude. Our observatory is at 90° W, indicating it is 90° west of this line.
Understanding the location helps astronomers predict what celestial objects can potentially be seen from a given observer's point on Earth, as it influences the horizon, zenith, and particular sky objects' positions at any given time.

Celestial declination is a key concept for determining which celestial objects can be observed from any location on Earth. It is akin to latitude in the celestial sphere, defining a star's position above or below the celestial equator. Measured in degrees from the equator, positive values indicate objects are north of it, and negative values tell us they are south.
No matter where you are on Earth, the observer's latitude plays a significant role in which declinations of stars they can see. Generally, stars with a declination are visible if it falls within a certain range of your location's latitude. Understanding this celestial coordinate is crucial for amateur and professional astronomers alike, as it forms the basis for many observational planning sessions.

Calculating the altitude of a celestial object is vital to determine its observability. Altitude refers to how high an object appears in the sky and is measured from 0° at the horizon to 90° at the zenith (the point directly above).
To calculate the altitude, we use the formula:

• \[\text{altitude} = 90^{\circ} - (\text{latitude} - \text{declination})\]

This formula computes how high in the sky, or whether at all, the object will appear.

• If the calculated altitude is above 0°, the object is above the horizon and can be seen.
• For altitudes below 0°, the object is below the horizon and thus, cannot be observed at that time.

Through simple calculations, astronomers determine which parts of the night sky are accessible from their observation spot. This process reflects the interplay between Earth's rotation and the fixed positions of distant celestial bodies.