Name: Partner(s): Day/Time: Version: detroit

# Timekeeping and Telescopes at the Detroit Observatory

A telescope that has a lens as its primary optical element, or objective, is a refracting telescope. A telescope that has a mirror as its objective is a reflecting telescope. Telescopes are described in more detail in the Daytime Observing at Angell Hall activity.

As you enter the Detroit Observatory, take note of the massive central telescope pier in the center of the first floor. The Fitz Telescope is resting on this pier, whose foundation is 15 feet below grade, and has a total height of roughly 60 feet. The pier is physically isolated from the rest of the building, so that vibrations in the building do not disturb the telescope pointing. All professional astronomical telescopes are built on similar piers.

### Part 1: The 12.6-inch Fitz Telescope

1. Is this telescope mounted for the altitude-azimuth or equatorial coordinate system? How can you tell?

2. Can this telescope point to any position on the sky? Can the dome provide a window to any position on the sky?

3. Is this telescope a refracting or reflecting telescope? How can you tell?

4. Telescopes allow the astronomer to collect more light than with the naked eye alone. The amount of light collected is proportional to the AREA of the primary lens or mirror in the system. Compare the collecting of the Fitz Telescope to the pupil of the human eye (0.16 inches)-- What is the ratio (hint, the area is proportional to diameter2)? Michigan's Magellan Telescopes in Chile have a diameter of 6.5m. Compare the collecting area of Magellan to the Fitz using ratios. 1m ~ 3.25 ft.

5. The second observatory director, Watson, was the biggest user of this telescope. Name at least one thing he did with it.

### Part 2: the Meridian Circle Telescope

This telescope is designed to accurately observe the transit of stars across the meridian. Note that the shutters open up to give a view of the meridian. The telescope can only point in declination, and not in right ascension. However, its mount is aligned north-south with the highest possible accuracy, and the eyepiece has fine lines to further note the crossing times of stars with exquisite precision.

1. Is this telescope a refractor or a reflector? How can you tell?

2. If you are standing in the doorway facing the meridian circle telescope, which direction are you facing (e.g. north, south-east, etc.) ? Which direction is north (e.g. left, forward, diagonal-behind-right, etc)?

3. Describe how the "harp" in the eyepiece is used.

4. How would you use this instrument to note the precise time of "noon" during the solar day, assuming one could view the Sun through the telescope w/o damage?

5. How can this telescope can be used to measure the length of a sidereal day?

6. Why would you want to have a telescope that can only point in altitude, and is fixed in azimuth (hint, consider the previous 2 questions, and how you answers would cage if you had to rotate the 'scope along both axes)?

Updated: 12/15/11 by JMM & SAM

Based on 105 version by MSO