<p><a href="https://ui.adsabs.harvard.edu/abs/1912LowOB...2...19S/abstract" rel="nofollow noreferrer">Slipher 1912</a> and
<a href="https://ui.adsabs.harvard.edu/abs/1912LowOB...2...17L/abstract" rel="nofollow noreferrer">Lowell 1912</a>
used a one-prism spectrograph on the 24-inch refractor at Lowell Observatory in this way.
Their 1911 observations of Uranus yielded a period of 10.8 hours, which made sense given the polar flattening previously observed by others.</p>

<p>They knew the obliquity of Uranus's satellites' orbits and assumed that its equator was in a similar plane.
This affected their observations in two ways.
First the solstice of 1901-02 presented an unfavorable pole-on aspect; after a negative result in 1903, Lowell waited until 1909 to try again.
Then Uranus required an unusual orientation of the spectrograph, so Slipher took special care to avoid instrument flexure bias.</p>

<p><a href="https://ui.adsabs.harvard.edu/abs/1930PASP...42..330M/abstract" rel="nofollow noreferrer">Moore and Menzel 1930</a> credited Slipher and Lowell with the first such observation and obtained a similar result themselves.</p>

CC BY-SA 4.0
2019-07-30T10:53:52.047Z
I've [added a plot](https://astronomy.stackexchange.com/a/32852/7982) to supplement your answer. If you'd like to use the script to make a better plot (zoom in on some dates) please feel free!
uhoh
CC BY-SA 4.0
2019-07-30T09:10:11.720Z
2019-07-30T09:10:11.720Z
Mike G
<p>This is a supplemental answer to <a href="https://astronomy.stackexchange.com/a/32849/7982">@MikeG's excellent answer</a>.</p>

<p>I've just plotted Uranus' axis direction versus the direction we view it at, to put those dates into context.</p>

<p>The "solstice of 1901-02" is clearly seen in the plot.</p>

<p><img src="https://i.sstatic.net/F6Ald.png" alt="Uranus from Earth versus spin axis"></p>

<p>Plotted using Python script based on <a href="https://rhodesmill.org/skyfield/" rel="nofollow noreferrer">Skyfield</a>:</p>

<pre><code>import numpy as np
import matplotlib.pyplot as plt

from skyfield.api import Loader, Star

halfpi, pi, twopi = [f*np.pi for f in (0.5, 1, 2)]
degs, rads        = 180/pi, pi/180

load  = Loader('~/Documents/fishing/SkyData')
ts    = load.timescale()

years    = np.arange(1800, 2100, 0.1)
times    = ts.utc(years, 1, 1)

de421    = load('de421.bsp')
de423    = load('de423.bsp')

Sun      = de423['sun']
Earth    = de423['earth']
Uranus   = de423['uranus barycenter']

Uranus_axis_RA_degs, Uranus_axis_Dec_degs = 257.311, -15.175 # https://link.springer.com/content/pdf/10.1007%2Fs10569-007-9072-y.pdf

RA, Dec, d = Earth.at(times).observe(Uranus).radec()

axis       = Star(ra_hours    = Uranus_axis_RA_degs * 24. / 360.,
                  dec_degrees = -15.175)
Axis_obs   = Earth.at(times).observe(axis)
Uranus_obs = Earth.at(times).observe(Uranus)
angle      = Uranus_obs.separation_from(Axis_obs)

brk        = np.abs(RA._degrees[1:] - RA._degrees[:-1]) &gt; 10.
RA, Dec    = RA._degrees[:-1], Dec._degrees[:-1]
RA[brk]    = np.nan

if True:
    plt.figure()
    plt.subplot(2, 1, 1)
    plt.plot(RA, Dec)
    plt.plot([Uranus_axis_RA_degs], [Uranus_axis_Dec_degs], 'ok')
    plt.xlim(0, 360)
    plt.ylim(-30, 30)
    plt.xlabel('RA (degs)', fontsize=16)
    plt.ylabel('Dec (degs)', fontsize=16)
    plt.subplot(2, 1, 2)
    plt.plot(years, angle.degrees)
    plt.xlabel('Year', fontsize=16)
    plt.ylabel('view vs axis (degs)', fontsize=16)
    plt.suptitle('Uranus from Earth versus spin axis', fontsize=16)
    plt.show()
</code></pre>

CC BY-SA 4.0
2019-07-30T10:52:39.773Z
2019-07-31T00:21:46.140Z
2019-07-31T00:21:46.140Z
uhoh
<p>As an undergraduate exercise quite a while ago, we placed the equator of Jupiter's disk across the slit of a high resolution grating spectrometer and then measured the tilt of the resulting line in order to estimate Jupiter's rotational velocity.</p>

<ol>
<li>When was an experiment of this type first performed for Uranus? </li>
<li>What was the result? Did it make sense at the time? Was Uranus' 98 degree axis tilt appreciated?</li>
</ol>

<p>Related: <a href="https://astronomy.stackexchange.com/q/32817/7982">Uranus' axis of rotation-when discovered?</a></p>

<spectroscopy><uranus>
First spectroscopic detection of Uranus' rotation?
uhoh
# First spectroscopic detection of Uranus' rotation?

(Asked by: username_0 on 2019-07-29)

As an undergraduate exercise quite a while ago, we placed the equator of Jupiter's disk across the slit of a high resolution grating spectrometer and then measured the tilt of the resulting line in order to estimate Jupiter's rotational velocity.

1. When was an experiment of this type first performed for Uranus?
2. What was the result? Did it make sense at the time? Was Uranus' 98 degree axis tilt appreciated?

Related: [Uranus' axis of rotation-when discovered?](https://astronomy.stackexchange.com/q/32817/7982)

**Tags:** spectroscopy, uranus


---

## 2 answers

### Answer by username_1 on 2019-07-30. Score: 2 | Accepted answer

[Slipher 1912](https://ui.adsabs.harvard.edu/abs/1912LowOB...2...19S/abstract) and
[Lowell 1912](https://ui.adsabs.harvard.edu/abs/1912LowOB...2...17L/abstract)
used a one-prism spectrograph on the 24-inch refractor at Lowell Observatory in this way.
Their 1911 observations of Uranus yielded a period of 10.8 hours, which made sense given the polar flattening previously observed by others.

They knew the obliquity of Uranus's satellites' orbits and assumed that its equator was in a similar plane.
This affected their observations in two ways.
First the solstice of 1901-02 presented an unfavorable pole-on aspect; after a negative result in 1903, Lowell waited until 1909 to try again.
Then Uranus required an unusual orientation of the spectrograph, so Slipher took special care to avoid instrument flexure bias.

[Moore and Menzel 1930](https://ui.adsabs.harvard.edu/abs/1930PASP...42..330M/abstract) credited Slipher and Lowell with the first such observation and obtained a similar result themselves.

> **Comments:**
> **username_0**: I've [added a plot](https://astronomy.stackexchange.com/a/32852/7982) to supplement your answer. If you'd like to use the script to make a better plot (zoom in on some dates) please feel free!  

---

### Answer by username_0 on 2019-07-30. Score: 1

This is a supplemental answer to @MikeG's excellent answer.
I've just plotted Uranus' axis direction versus the direction we view it at, to put those dates into context.
The "solstice of 1901-02" is clearly seen in the plot.

Plotted using Python script based on Skyfield:
import numpy as np
import matplotlib.pyplot as plt

from skyfield.api import Loader, Star

halfpi, pi, twopi = [f*np.pi for f in (0.5, 1, 2)]
degs, rads        = 180/pi, pi/180

load  = Loader('~/Documents/fishing/SkyData')
ts    = load.timescale()

years    = np.arange(1800, 2100, 0.1)
times    = ts.utc(years, 1, 1)

de421    = load('de421.bsp')
de423    = load('de423.bsp')

Sun      = de423['sun']
Earth    = de423['earth']
Uranus   = de423['uranus barycenter']

Uranus_axis_RA_degs, Uranus_axis_Dec_degs = 257.311, -15.175 # https://link.springer.com/content/pdf/10.1007%2Fs10569-007-9072-y.pdf

RA, Dec, d = Earth.at(times).observe(Uranus).radec()

axis       = Star(ra_hours    = Uranus_axis_RA_degs * 24. / 360.,
                  dec_degrees = -15.175)
Axis_obs   = Earth.at(times).observe(axis)
Uranus_obs = Earth.at(times).observe(Uranus)
angle      = Uranus_obs.separation_from(Axis_obs)

brk        = np.abs(RA._degrees[1:] - RA._degrees[:-1]) > 10.
RA, Dec    = RA._degrees[:-1], Dec._degrees[:-1]
RA[brk]    = np.nan

if True:
    plt.figure()
    plt.subplot(2, 1, 1)
    plt.plot(RA, Dec)
    plt.plot([Uranus_axis_RA_degs], [Uranus_axis_Dec_degs], 'ok')
    plt.xlim(0, 360)
    plt.ylim(-30, 30)
    plt.xlabel('RA (degs)', fontsize=16)
    plt.ylabel('Dec (degs)', fontsize=16)
    plt.subplot(2, 1, 2)
    plt.plot(years, angle.degrees)
    plt.xlabel('Year', fontsize=16)
    plt.ylabel('view vs axis (degs)', fontsize=16)
    plt.suptitle('Uranus from Earth versus spin axis', fontsize=16)
    plt.show()


---

