How to use an astrolabe in the daytime

Michael Robinson
18 Mar 202007:33
EducationalLearning
32 Likes 10 Comments

TLDRThis instructional video demonstrates the use of a laser-cut astrolabe, a medieval astronomical tool, to determine the time of day and the Sun's position in the sky. The presenter explains how to take a Sun sighting for its elevation, align the astrolabe with the current date, and adjust for the Earth's elliptical orbit using the 'equation of time'. The video also shows how to read local time, compass directions, and the Sun's azimuth, highlighting the astrolabe's utility as a versatile navigational device.

Takeaways
  • πŸ“… The video is about using an astrolabe, a tool for astronomical navigation, and the speaker has two different sizes available on their GitHub page.
  • πŸ” The large astrolabe has simpler printing, while the small one has a simplified star chart with labeled stars for easier identification.
  • β˜€οΈ The demonstration focuses on using the astrolabe during the daytime, primarily with the Sun as the visible 'star', which moves throughout the year.
  • πŸ‘€ To take a sighting of the Sun's elevation, one must use the back of the astrolabe and align the pointer's wings to create a shadow, avoiding direct eye contact with the Sun.
  • πŸ“ The Sun's elevation is read from the astrolabe's elevation scale, which helps in determining its position in the sky.
  • πŸ“† The astrolabe has a calendar feature to identify the current date, which is crucial for aligning the Sun's position accurately.
  • πŸ—ΊοΈ The offset circle on the astrolabe represents the Sun's apparent orbit, and the pointer must be adjusted to match the Sun's current elevation.
  • πŸ•’ The time of day can be determined by reading the outer ring of the astrolabe, which provides local time based on the Sun's position.
  • ⏰ The 'equation of time' curve on the astrolabe corrects for discrepancies between solar time and clock time due to the Earth's elliptical orbit and axial tilt.
  • 🧭 The outer ring of the astrolabe also functions as a compass, indicating cardinal directions and the Sun's azimuthal position.
  • πŸ“± The astrolabe is likened to the medieval equivalent of a smartphone, highlighting its multifunctional use in navigation and timekeeping.
Q & A

  • What is the main purpose of using an astrolabe as shown in the video?

    -The main purpose of using an astrolabe in the video is to measure the Sun's elevation during the daytime and to calculate the local time, as well as other astronomical data such as the Sun's position in the sky.

  • What are the two different sizes of astrolabes mentioned in the video?

    -The video mentions a large astrolabe and a small one, with the large one having simpler printing and the small one having a simplified star chart with labeled stars for easier identification.

  • How does the astrolabe help compensate for the Sun's movement throughout the year?

    -The astrolabe compensates for the Sun's movement by having a calendar and an offset circle that shows the apparent orbit of the Sun through the sky, allowing users to align the astrolabe with the current date and Sun's elevation.

  • What is the correct way to take a sighting of the Sun's elevation using the astrolabe?

    -To take a sighting of the Sun's elevation, one should use the back of the astrolabe, align the pointer's wings to make a shadow, and ensure they are on top of each other without looking down the pointer to avoid eye damage.

  • Why is it important to know the date when using the astrolabe for time calculation?

    -Knowing the date is important because the astrolabe uses the date to align with the Sun's apparent orbit, which changes over the course of the year, to accurately calculate the local time.

  • How can you determine the local time using the astrolabe?

    -After aligning the astrolabe with the correct date and Sun's elevation, you can read the local time from the outer ring of the astrolabe, taking into account any adjustments for daylight savings time.

  • What is the 'equation of time' and how does it relate to the astrolabe?

    -The 'equation of time' is a kidney bean-shaped curve on the astrolabe that accounts for the differences between solar time and clock time due to the Earth's elliptical orbit and axial tilt, helping to correct the time read from the astrolabe.

  • How can the astrolabe be used to find the Sun's position in the sky?

    -The astrolabe can be used to find the Sun's position by aligning the pointer with the Sun's apparent orbit on the offset circle and reading the intersection point with the elevation contours, which indicate the Sun's location in the sky.

  • What is the purpose of the compass on the astrolabe?

    -The compass on the astrolabe helps to determine the cardinal directions (North, South, East, and West) and can be used to find the Sun's azimuth, or the angle between the Sun and true North.

  • How does the astrolabe's design help in measuring the Sun's elevation and position?

    -The astrolabe's design includes an elevation scale, pointer with wings for alignment, and an offset circle for the Sun's apparent orbit, all of which work together to measure the Sun's elevation and position in the sky accurately.

Outlines
00:00
🌞 Daytime Use of an Astrolabe

This paragraph demonstrates how to use an astrolabe during the daytime to measure the Sun's elevation. The speaker introduces two different astrolabes, a large one with simpler printing and a smaller one with labeled stars for easier identification. The focus is on the large astrolabe for visibility. The process involves aligning the astrolabe's pointer with the Sun's shadow to measure its elevation angle, which in this case is about 26 degrees. The user is also instructed on how to adjust the astrolabe to the current date, March 18th, to account for the Sun's apparent movement throughout the year. By aligning the date with the Sun's position on the offset circle, the user can determine the local time, which is approximately 9:20 AM after adjusting for daylight saving time.

05:02
πŸ•° Adjusting for Earth's Orbital Anomalies

The second paragraph explains the need to adjust for the Earth's elliptical orbit and axial tilt when using the astrolabe to determine accurate time. The 'kidney bean' shaped curve, known as the 'equation of time,' is used to correct the discrepancy between solar time and clock time. By finding the date, March 18th, on the astrolabe and reading the offset, the user learns the Sun is running approximately 10 minutes slow, adjusting the time to about 9:40 AM considering daylight saving time. Additionally, the astrolabe can be used as a compass to determine the Sun's方位, which in this case is 125 degrees azimuth. The paragraph concludes by emphasizing the versatility of the astrolabe, likening it to a medieval smartphone, and thanks the viewer for watching.

Mindmap
Keywords
πŸ’‘Astrolabe
An astrolabe is an ancient astronomical instrument used for solving problems related to time and the position of the stars. In the video, the astrolabe is the central tool demonstrated for its use in determining the time of day and the Sun's position in the sky. The script mentions two different sizes of astrolabes available on the presenter's GitHub page, indicating their practical use in astronomy.
πŸ’‘Elevation
Elevation, in the context of the video, refers to the angle of the Sun above the horizon. The script describes how to measure the Sun's elevation using the astrolabe's elevation scale, which is crucial for determining the time and the Sun's position accurately. For instance, the Sun's elevation is measured at about 26 degrees in the demonstration.
πŸ’‘Sighting
A sighting is the act of aligning an instrument to observe a celestial body. The video script explains the process of taking a sighting of the Sun's elevation using the astrolabe's pointer, which involves aligning the 'wings' of the pointer to create a single shadow, indicating the exact angle of the Sun.
πŸ’‘Calendar
The calendar mentioned in the script is part of the astrolabe's design, used to account for the changing position of the Sun throughout the year. The astrolabe has markings for each month and specific dates, which are essential for adjusting the instrument to match the current date, as demonstrated with the date March 18th.
πŸ’‘Offset Circle
The offset circle on the astrolabe represents the apparent orbit of the Sun across the sky. The script describes how to use this feature to determine the Sun's position in the sky on a specific date, by aligning the date with the Sun's elevation, which helps in finding the local time.
πŸ’‘Elevation Contours
Elevation contours on the astrolabe are markings that indicate different angles of elevation. The script explains that these contours are used to fine-tune the Sun's position in the sky, with the example given that the large astrolabe has contours every 2 degrees, aiding in precise measurements.
πŸ’‘Local Time
Local time is the time of day based on the observer's position relative to the Sun. The video script demonstrates how to use the astrolabe to find the local time by aligning the date and the Sun's elevation, with the example of reading 8:20 a.m., adjusted for daylight savings time to 9:20 a.m.
πŸ’‘Equation of Time
The equation of time is a concept that accounts for the difference between clock time and solar time due to the elliptical shape of the Earth's orbit and its axial tilt. The script describes a 'kidney bean' shaped curve on the astrolabe that represents the equation of time, used to correct the time read from the astrolabe to match the time on a clock.
πŸ’‘Compass
A compass, as mentioned in the script, is a tool for determining direction, and the astrolabe has a compass feature that helps in finding the Sun's方位 (position) in the sky. The script explains how to read the compass on the astrolabe to determine the Sun's azimuth, or the angle between the Sun and true North.
πŸ’‘Azimuth
Azimuth is the angle between an object in the sky and a reference direction, typically true North. The video script uses the term to describe how to find the Sun's position in the sky by reading the compass markings on the astrolabe, with the example of the Sun being located at 125 degrees azimuth.
Highlights

Introduction to using a laser-cut astrolabe, with two different sizes available on GitHub.

The large astrolabe has simpler printing, while the small one has a simplified star chart with labeled stars for easier identification.

Demonstration of using the astrolabe during the daytime, focusing on the Sun's position as it is the only visible 'star'.

Explanation of how the Sun's position changes throughout the year and the astrolabe's role in compensating for this movement.

Step-by-step guide on taking a sighting of the Sun's elevation using the astrolabe's back and the elevation scale.

Important safety note: Do not look down the pointer at the Sun to avoid eye damage.

Technique for aligning the astrolabe's pointer by matching the shadows of its wings to determine the Sun's exact elevation.

How to read the Sun's elevation from the astrolabe and the example of it being approximately 26 degrees.

Instructions on using the astrolabe's calendar feature to determine the current date and its position on the astrolabe.

Process of aligning the astrolabe's pointer to match the Sun's current position in the sky based on the date and elevation.

Explanation of the offset circle and its representation of the Sun's apparent orbit in the sky.

How to use the elevation contours to find the Sun's exact location in the sky on a given date.

Reading local time from the astrolabe and adjusting for daylight savings time.

Introduction to the 'equation of time' and its role in correcting the difference between solar time and clock time.

How to read the 'equation of time' to adjust the Sun's position and get an accurate time reading.

Use of the astrolabe as a compass to determine the Sun's azimuth and its location in the sky.

Final thoughts on the astrolabe's capabilities and its comparison to a medieval smartphone.

Transcripts

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Astrolabe UseNavigation ToolTimekeepingSun ElevationCelestial MappingDIY ProjectEducational VideoOutdoor LearningHistorical ToolMedieval Tech