Why is the "north" in the sun photo not necessarily directly above the picture?
The sun's rotation axis has its own tilt, and the sun's surface also has coordinates like the earth's longitude and latitude lines.
When analyzing photos of the sun, you need to know which side is the solar north pole and which solar longitude the center of the disk faces. We first draw longitude and latitude lines for a digital sun, and then put an imaginary spot to see when the same sun's position turns to the front or back.
Guess first
Is the north pole direction of the sun always exactly the same as the north direction in the photo?
Show answer and explanation
uncertain — The sun's axis of rotation is tilted relative to the north direction of the celestial sphere, described by P.
Then connect experience and science
First distinguish between the celestial north and the solar north pole
The upper part of the picture is fixed to the celestial north, and the golden axis marks the axis of rotation of the sun. P represents the angle between the two.
P = x + y
We sometimes look slightly north or south of the sun
B0 is the latitude of the sun at the center of the disk. A positive value means that the solar north pole is slightly facing the earth. It is not the latitude of an Earth observer.
sin B₀ = sin(λ−K) sin I
The longitude lines follow the sun as it turns towards the front
L0 gives the current longitude of the sun facing the Earth. Spots are placed at fixed latitude and longitude and are drawn only in the visible hemisphere.
L₀ = η − θ (normalized)
Number the rotation period
Carrington longitude is defined using a fixed sidereal period of 25.38 days; the corresponding average synodic period is about 27.2752 days. There is still a periodic correction at the beginning.
JDE ≈ 2398140.2270 + 27.2752316 C + period correction
P is the position angle of the sun's rotation axis in the sky, B₀ is the central latitude of the sun, and L₀ is the central longitude. The three describe different directions; first calculate the axis and node directions related to the date, and then normalize the longitude. There is another cycle correction at the starting point of the Carrington Week.
give it a try
Fixed spot latitude and longitude, changed date. The bright spot will only appear when it is turned toward the hemisphere facing the Earth; the Sun's North Pole axis will also be tilted relative to the celestial north.
No need to memorize symbols
- P
- The direction of the north pole of the sun is relative to the north, and eastward is positive
- B₀
- Solar latitude of disk center
- L₀
- Carrington longitude of the disk center
- C
- Carrington rotation period integer number
Algorithm, accuracy and scope of application
Realize the starting time of P, B0, L0 and 29.1/29.2 of the Carrington rotation cycle in Chapter 29. Enter Chapter 25 Appendix III earthVSOP Earth's geometric yellow longitude +180°, subtract 20.4898″/R to get the solar retinoid longitude without nutation; P then uses the nutated yellow longitude and true yellow longitude. Consistent with the original book and AA+, this route is not mixed with the solar FK5 latitude correction or home page ephemeris. Original book 29.a Add 59 seconds from UT to TD, 29. b Output JDE, if you change to UT, add 51 seconds. The solar spot projection consists of longitude and latitude and P/B0/L0. The spots are imaginary fixed coordinates and do not simulate real sunspot evolution, differential rotation or local parallax angle. The rotation period is approximately limited to the purpose of the original book 1850-2100; images are not used to replace safety solar observation equipment.
my understanding check
Is B0 the latitude of the observer on Earth?
No, it’s the solar latitude of the center of the sun’s disk — It describes where we look toward the surface of the sun.
What should the picture look like after the spots have been turned to the back?
Hidden and explained on the back — The hemisphere blocked by the Sun itself cannot be seen directly.
Are the spots in this lesson real-time sunspot data?
No, it is an experimental mark to fix the position of the sun. — Real sunspots will evolve, and the sun will also rotate differentially. This lesson only calculates the observation geometry.
Determine how the Sun's axis is tilted and which longitude lines face the Earth, and then interpret the position in the solar image.
Jean Meeus · Astronomical Algorithms, 2nd ed. · No. 29 chapter