APOD: Solar Analemma 2024 (2025 Jan 02)

[APOD Robot]

Solar Analemma 2024

Explanation: Recorded during 2024, this year-spanning series of images reveals a pattern in the seasonal drift of the Sun's daily motion through planet Earth's sky. Known to some as an analemma, the figure-eight curve was captured in exposures taken only at 1pm local time on clear days from Kayseri, Turkiye. Of course the Sun's position on the 2024 solstice dates was at the top and bottom of the curve. They correspond to the astronomical beginning of summer and winter in the north. The points along the curve half-way between the solstices, but not the figure-eight curve crossing point, mark the 2024 equinoxes and the start of spring and fall. Regional peaks and dormant volcano Mount Erciyes lie along the southern horizon in the 2024 timelapse skyscape.

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[mfavret]

One of the date mentionned on this picture is obviously false : the bottom of the analemma is the position of the Sun at winter solstice (20/12/2024) but the text is "01/09".

[Chris Peterson]

One of the date mentionned on this picture is obviously false : the bottom of the analemma is the position of the Sun at winter solstice (20/12/2024) but the text is "01/09".

2024-01-09 is close to the northern winter solstice 2023-12-21. Presumably the dates listed for the equinox images were the closest obtainable given weather or other factors.

[JWP456]

Actually, the text on the photo merely reads "Solar Analemma 13.00 (GMT +3) 09.01.2024-22.12.2024", presumably indicating those were the first and last dates on which the photos in the series were taken rather than the dates of successive winter solstices. As suggested by Chris Peterson, the nine day gaps at the beginning and end of the year (and seen elsewhere in the pattern) could be due to inclement weather, etc.

[johnnydeep]

How is "half way between the soltices defined "? I see this Pic in the Wikipedia link but can't relate it to this apod:

Click to view full size image

Is it just based on degrees altitude? What does the Φ symbol mean?

[Chris Peterson]

How is "half way between the soltices defined "? I see this Pic in the Wikipedia link but can't relate it to this apod:

Click to view full size image

Is it just based on degrees altitude? What does the Φ symbol mean?

Draw a line between the solstice points, divide it in half, and draw another line through that point, perpendicular to the solstice axis. That should define the equinox axis. Φ is the equator, with the solstices defined by that plus or minus the Earth's axial tilt, ε.

[raschumacher]

Is there a particular orbital feature associated with the crossing point? I've never fully understood the geometry of the analemma.

[johnnydeep]

How is "half way between the soltices defined "? I see this Pic in the Wikipedia link but can't relate it to this apod:

Click to view full size image

Is it just based on degrees altitude? What does the Φ symbol mean?

Draw a line between the solstice points, divide it in half, and draw another line through that point, perpendicular to the solstice axis. That should define the equinox axis. Φ is the equator, with the solstices defined by that plus or minus the Earth's axial tilt, ε.

The equator of what?

[johnnydeep]

Is there a particular orbital feature associated with the crossing point? I've never fully understood the geometry of the analemma.

Don't feel bad. The dreaded analemma has been eluding my understanding for decades now.

[Chris Peterson]

Is there a particular orbital feature associated with the crossing point? I've never fully understood the geometry of the analemma.

No single feature. The structure of the analemma is a consequence of the eccentricity of Earth's orbit (which is not perfectly circular), the tilt of Earth's axis, and where in the orbit the equinoxes occur relative to when we're closest to the Sun. Vary any of these, and the shape of the analemma will change.

[Chris Peterson]

How is "half way between the soltices defined "? I see this Pic in the Wikipedia link but can't relate it to this apod:

Click to view full size image

Is it just based on degrees altitude? What does the Φ symbol mean?

Draw a line between the solstice points, divide it in half, and draw another line through that point, perpendicular to the solstice axis. That should define the equinox axis. Φ is the equator, with the solstices defined by that plus or minus the Earth's axial tilt, ε.

The equator of what?

The celestial equator. That is, the projection of Earth's equator on the sky.

[johnnydeep]

Is there a particular orbital feature associated with the crossing point? I've never fully understood the geometry of the analemma.

No single feature. The structure of the analemma is a consequence of the eccentricity of Earth's orbit (which is not perfectly circular), the tilt of Earth's axis, and where in the orbit the equinoxes occur relative to when we're closest to the Sun. Vary any of these, and the shape of the analemma will change.

Would be cool to have a web app that allowed you to change any of those parameters with sliders and see the change in the analemma that results!

[johnnydeep]

Draw a line between the solstice points, divide it in half, and draw another line through that point, perpendicular to the solstice axis. That should define the equinox axis. Φ is the equator, with the solstices defined by that plus or minus the Earth's axial tilt, ε.

The equator of what?

The celestial equator. That is, the projection of Earth's equator on the sky.

Ah, thanks.

[Chris Peterson]

Is there a particular orbital feature associated with the crossing point? I've never fully understood the geometry of the analemma.

No single feature. The structure of the analemma is a consequence of the eccentricity of Earth's orbit (which is not perfectly circular), the tilt of Earth's axis, and where in the orbit the equinoxes occur relative to when we're closest to the Sun. Vary any of these, and the shape of the analemma will change.

Would be cool to have a web app that allowed you to change any of those parameters with sliders and see the change in the analemma that results!

Did you look?

https://mtirado.com/resources/analemma-calc/
https://alokm.com/astro/analemmagenerator.html

[johnnydeep]

No single feature. The structure of the analemma is a consequence of the eccentricity of Earth's orbit (which is not perfectly circular), the tilt of Earth's axis, and where in the orbit the equinoxes occur relative to when we're closest to the Sun. Vary any of these, and the shape of the analemma will change.

Would be cool to have a web app that allowed you to change any of those parameters with sliders and see the change in the analemma that results!

Did you look?

https://mtirado.com/resources/analemma-calc/
https://alokm.com/astro/analemmagenerator.html

Wow, very cool! Thanks!! ( I had figured there was no way there'd be one out there already, let alone several. )

[raschumacher]

No single feature. The structure of the analemma is a consequence of the eccentricity of Earth's orbit (which is not perfectly circular), the tilt of Earth's axis, and where in the orbit the equinoxes occur relative to when we're closest to the Sun. Vary any of these, and the shape of the analemma will change.

Would be cool to have a web app that allowed you to change any of those parameters with sliders and see the change in the analemma that results!

Did you look?

https://mtirado.com/resources/analemma-calc/
https://alokm.com/astro/analemmagenerator.html

Ditto thanks. It didn't occur to me either to look for such a tool.

[Chris Peterson]

Would be cool to have a web app that allowed you to change any of those parameters with sliders and see the change in the analemma that results!

Did you look?

https://mtirado.com/resources/analemma-calc/
https://alokm.com/astro/analemmagenerator.html

Ditto thanks. It didn't occur to me either to look for such a tool.

Never underestimate the ability of the Internet to provide a calculator for just about anything you can think of.

[johnnydeep]

Did you look?

https://mtirado.com/resources/analemma-calc/
https://alokm.com/astro/analemmagenerator.html

Ditto thanks. It didn't occur to me either to look for such a tool.

Never underestimate the ability of the Internet to provide a calculator for just about anything you can think of.

[paulocarvalhoRJ]

Please, try to use a singe date format. There are three different formats in this APOD, which is very confusing.

[Chris Peterson]

Please, try to use a singe date format. There are three different formats in this APOD, which is very confusing.

The APOD only appears to use one date format.

[johnnydeep]

Please, try to use a singe date format. There are three different formats in this APOD, which is very confusing.

The APOD only appears to use one date format.

I see two. The format on the analemma itself is mm/dd/yyyyy and the one in the bottom right text box is dd/mm/yyyy.

[Chris Peterson]

Please, try to use a singe date format. There are three different formats in this APOD, which is very confusing.

The APOD only appears to use one date format.

I see two. The format on the analemma itself is mm/dd/yyyyy and the one in the bottom right text box is dd/mm/yyyy.

Ah, right. I wish everyone submitting APODs would use ISO standard date notation, yyyy-mm-dd. But I'm not going to hold my breath.

[johnnydeep]

The APOD only appears to use one date format.

I see two. The format on the analemma itself is mm/dd/yyyyy and the one in the bottom right text box is dd/mm/yyyy.

Ah, right. I wish everyone submitting APODs would use ISO standard date notation, yyyy-mm-dd. But I'm not going to hold my breath.

Yup. The yyyy-mm-dd format is also preferred by this former software engineer, since it makes dates sort alphabetically chronologically, and if the dashes are omitted, they also sort numerically chronologically!