As the expanding universe cooled, the first neutral1 hydrogen atoms formed about 380,000 years after the Big Bang (ABB), and most of the hydrogen in the universe remained neutral until the first stars began forming at least 65 million years ABB.

The period of time from 380,000 to 65 million years or so ABB is referred to as the “dark ages” since at the beginning of this period the cosmic background radiation from the Big Bang had redshifted from visible light to infrared so the universe was truly dark (in visible light) until the first stars began to form at the end of this period.

All the while, neutral hydrogen atoms occasionally undergo a “spin-flip” transition where the electron transitions from the higher-energy hyperfine level of the ground state to the lower-energy hyperfine level, and a microwave photon of wavelength 21.1061140542 cm and frequency 1420.4057517667 MHz is emitted.

Throughout the dark ages, the 21 cm emission line was being emitted by the abundant neutral hydrogen throughout the universe, but as the universe continued to expand the amount of cosmological redshift between the time of emission and the present day has been constantly changing. The longer ago the 21 cm emission occurred, the greater the redshift to longer wavelengths. We thus have a great way to map the universe during this entire epoch by looking at the “spectrum” of redshifts of this particular spectral line.

380,000 and 65 million years ABB correspond to a cosmological redshift (z) of 1,081 and 40, respectively. We can calculate what the observed wavelength and frequency of the 21 cm line would be for the beginning and end of the dark ages.

$\lambda _{obs} = (z+1)\cdot \lambda_{emit}$

The observed wavelength (λobs) for the 21 cm line (λemit) at redshift (z) of 1,081 using the above equation gives us 22,836.8 cm or 228.4 meters.

$\nu = \frac{c}{\lambda }$

That gives us a frequency (ν) of 1.3 MHz (using the equation above), where the speed of light c = 299,792,458 meters per second.

So a 21 cm line emitted 380,000 years ABB will be observed to have a wavelength of 228.4 m and a frequency of 1.3 MHz.

Using the same equations, we find that a 21 cm line emitted 65 Myr ABB will be observed to have a wavelength of 8.7 m and a frequency of 34.7 MHz.

We thus will be quite interested in taking a detailed look at radio waves in the entire frequency range 1.3 – 34.7 MHz, with corresponding wavelengths from 228.4 m down to 8.7 m.2

The interference from the Earth’s ionosphere and the ever-increasing cacophony of humanity’s radio transmissions makes observing these faint radio signals all but impossible from anywhere on or near the Earth. Radio astronomers and observational cosmologists are planning to locate radio telescopes on the far side of the Moon—both on the surface and in orbit above it—where the entire mass of the Moon will effectively block all terrestrial radio interference. There we will finally hear the radio whispers of matter before the first stars formed.

1 By “neutral” we mean hydrogen atoms where the electron has not been ionized and resides in the ground state—not an excited state.

2 Incidentally, the 2.7 K cosmic microwave background radiation which is the “afterglow” of the Big Bang itself at the beginning of the dark ages (380,000 years ABB), peaks at a frequency between 160 and 280 GHz and a wavelength around 1 – 2 mm. So this is a much higher frequency and shorter wavelength than the redshifted 21 cm emissions we are proposing to observe here.

References

Ananthaswamy, Anil, “The View from the Far Side of the Moon”, Scientific American, April 2021, pp. 60-63. https://www.scientificamerican.com/article/telescopes-on-far-side-of-the-moon-could-illuminate-the-cosmic-dark-ages1/

Burns, Jack O., et al., “Global 21-cm Cosmology from the Farside of the Moon”, https://arxiv.org/ftp/arxiv/papers/2103/2103.05085.pdf

Koopmans, Léon, et al., “Peering into the Dark (Ages) with Low-Frequency Space Interferometers”, https://arxiv.org/ftp/arxiv/papers/1908/1908.04296.pdf

Ned Wright’s Javascript Cosmology Calculator, http://www.astro.ucla.edu/~wright/CosmoCalc.html

## Video Meteors 2020 – II

During the second half of 2020, I serendipitously captured six meteors on my telescope’s 17 x 11 arcminute video field of view while observing potential asteroid occultation events. I used the method described in There’s a Meteor in My Image to determine the radiant for each meteor. Here they are.

A sporadic meteor is any meteor that does not come from a known radiant.

None of these meteors were particularly bright, unfortunately, so you may want to use the full-screen button at the lower-right-hand corner of each video to see them well.

References

International Meteor Organization, 2o2o Meteor Shower Calendar, Jürgen Rendtel, ed. https://www.imo.net/files/meteor-shower/cal2020.pdf.

## Supernovae in the Milky Way

The first recorded supernova in our Milky Way galaxy (or anywhere else, for that matter) was seen to blaze forth in the constellation Centaurus by astute Chinese astronomers in 185 AD. Including that one, only seven confirmed supernovae have been observed in our Milky Way galaxy, though thousands are discovered each year in other galaxies.

Supernova light reached Earth in AD 185, 393, 1006, 1054, 1181, 1572, and 1604. All seven of these events occurred before the invention of the telescope. Are we overdue for another supernova? Well, given this ridiculously small sample, we can endeavor to do some simple “statistics”. The shortest recorded interval between two Milky Way supernovae was 32 years between 1572 and 1604. The longest interval has been 613 years, between the supernovae of 393 and 1006 (assuming none went unnoticed). On average then (such as it is), we “should” have seen a Milky Way supernova around 1841, and using the longest interval of 613 years, we might be expecting one by the year 2217. Undoubtedly, some supernovae in the Milky Way have escaped detection because they lay behind thick interstellar clouds.

The big mystery to me is why are there no recorded supernova events prior to 185 AD? The earliest extant records of astronomical events go back at least as far as 2316 BC (a comet in the constellation Crater was recorded by Chinese astronomers), but in the intervening 2,500 years there has been no mention of anything that could be attributed to a supernova. Or has there? Some writings before and after 185 AD suggest possible supernovae, but until a supernova remnant is identified, we need to look for other explanations.

Here follows a table of the known observed Milky Way supernovae. Of course, other supernova remnants have been discovered in our Milky Way galaxy, but no record has yet been discovered describing these events. Many of them predate recorded history.

In the table below, you’ll note that these supernovae tend to lie close to the galactic plane (galactic latitude b = 0°)—not at all surprising considering that’s where most of the stars are.

## Zodiacal Light 2021

In 2021, the best dates and times for observing the zodiacal light are listed in the calendar below. The sky must be very clear with little or no light pollution. The specific times listed are for Dodgeville, Wisconsin (42° 58′ N, 90° 08′ W).

Here’s a nicely-formatted printable PDF file of the zodiacal light calendar:

 January 2021
SUN MON TUE WED THU FRI SAT
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
Zodiacal Light 6:49 – 7:26 p.m. West
31
Zodiacal Light 6:50 – 7:50 p.m. West

 February 2021
SUN MON TUE WED THU FRI SAT
1
Zodiacal Light 6:51 – 7:51 p.m. West
2
Zodiacal Light 6:52 – 7:52 p.m. West
3
Zodiacal Light 6:53 – 7:53 p.m. West
4
Zodiacal Light 6:54 – 7:54 p.m. West
5
Zodiacal Light 6:56 – 7:56 p.m. West
6
Zodiacal Light 6:57 – 7:57 p.m. West
7
Zodiacal Light 6:58 – 7:58 p.m. West
8
Zodiacal Light 6:59 – 7:59 p.m. West
9
Zodiacal Light 7:00 – 8:00 p.m. West
10
Zodiacal Light 7:02 – 8:02 p.m. West
11
Zodiacal Light 7:03 – 8:03 p.m. West
12
Zodiacal Light 7:04 – 8:04 p.m. West
13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28
Zodiacal Light 7:23 – 7:36 p.m. West

 March 2021
SUN MON TUE WED THU FRI SAT
1
Zodiacal Light 7:25 – 8:25 p.m. West
2
Zodiacal Light 7:26 – 8:26 p.m. West
3
Zodiacal Light 7:27 – 8:27 p.m. West
4
Zodiacal Light 7:28 – 8:28 p.m. West
5
Zodiacal Light 7:29 – 8:29 p.m. West
6
Zodiacal Light 7:31 – 8:31 p.m. West
7
Zodiacal Light 7:32 – 8:32 p.m. West
8
Zodiacal Light 7:33 – 8:33 p.m. West
9
Zodiacal Light 7:34 – 8:34 p.m. West
10
Zodiacal Light 7:36 – 8:36 p.m. West
11
Zodiacal Light 7:37 – 8:37 p.m. West
12
Zodiacal Light 7:38 – 8:38 p.m. West
13
Zodiacal Light 7:40 – 8:40 p.m. West
14
Zodiacal Light 8:41 – 9:41 p.m. West
15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30
Zodiacal Light 9:03 – 10:03 p.m. West
31
Zodiacal Light 9:04 – 10:04 p.m. West

 April 2021
SUN MON TUE WED THU FRI SAT
1
Zodiacal Light 9:05 – 10:05 p.m. West
2
Zodiacal Light 9:07 – 10:07 p.m. West
3
Zodiacal Light 9:08 – 10:08 p.m. West
4
Zodiacal Light 9:10 – 10:10 p.m. West
5
Zodiacal Light 9:11 – 10:11 p.m. West
6
Zodiacal Light 9:13 – 10:13 p.m. West
7
Zodiacal Light 9:14 – 10:14 p.m. West
8
Zodiacal Light 9:16 – 10:16 p.m. West
9
Zodiacal Light 9:17 – 10:17 p.m. West
10
Zodiacal Light 9:19 – 10:19 p.m. West
11
Zodiacal Light 9:20 – 10:20 p.m. West
12
Zodiacal Light 9:22 – 10:22 p.m. West
13
Zodiacal Light 9:24 – 10:24 p.m. West
14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30

 May 2021
SUN MON TUE WED THU FRI SAT
1
2 3 4 5 6 7 8
9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25 26 27 28 29
30 31

 June 2021
SUN MON TUE WED THU FRI SAT
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30

 July 2021
SUN MON TUE WED THU FRI SAT
1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 31

 August 2021
SUN MON TUE WED THU FRI SAT
1 2 3 4 5 6 7
8 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31

 September 2021
SUN MON TUE WED THU FRI SAT
1 2 3 4
5 6
Zodiacal Light 3:52 – 4:52 a.m. East
7
Zodiacal Light 3:53 – 4:53 a.m. East
8
Zodiacal Light 3:54 – 4:54 a.m. East
9
Zodiacal Light 3:56 – 4:56 a.m. East
10
Zodiacal Light 3:57 – 4:57 a.m. East
11
Zodiacal Light 3:58 – 4:58 a.m. East
12
Zodiacal Light 4:00 – 5:00 a.m. East
13
Zodiacal Light 4:01 – 5:01 a.m. East
14
Zodiacal Light 4:02 – 5:02 a.m. East
15
Zodiacal Light 4:04 – 5:04 a.m. East
16
Zodiacal Light 4:05 – 5:05 a.m. East
17
Zodiacal Light 4:06 – 5:06 a.m. East
18
Zodiacal Light 4:08 – 5:08 a.m. East
19
Zodiacal Light 4:59 – 5:09 a.m. East
20 21 22 23 24 25
26 27 28 29 30

 October 2021
SUN MON TUE WED THU FRI SAT
1 2
3 4 5
Zodiacal Light 4:28 – 5:28 a.m. East
6
Zodiacal Light 4:30 – 5:30 a.m. East
7
Zodiacal Light 4:31 – 5:31 a.m. East
8
Zodiacal Light 4:32 – 5:32 a.m. East
9
Zodiacal Light 4:33 – 5:33 a.m. East
10
Zodiacal Light 4:34 – 5:34 a.m. East
11
Zodiacal Light 4:35 – 5:35 a.m. East
12
Zodiacal Light 4:37 – 5:37 a.m. East
13
Zodiacal Light 4:38 – 5:38 a.m. East
14
Zodiacal Light 4:39 – 5:39 a.m. East
15
Zodiacal Light 4:40 – 5:40 a.m. East
16
Zodiacal Light 4:41 – 5:41 a.m. East
17
Zodiacal Light 4:42 – 5:42 a.m. East
18
Zodiacal Light 5:03 – 5:43 a.m. East
19 20 21 22 23
24 25 26 27 28 29 30
31

 November 2021
SUN MON TUE WED THU FRI SAT
1 2 3 4
Zodiacal Light 5:03 – 6:03 a.m. East
5
Zodiacal Light 5:04 – 6:04 a.m. East
6
Zodiacal Light 5:05 – 6:05 a.m. East
7
Zodiacal Light 4:06 – 5:06 a.m. East
8
Zodiacal Light 4:07 – 5:07 a.m. East
9
Zodiacal Light 4:08 – 5:08 a.m. East
10
Zodiacal Light 4:09 – 5:09 a.m. East
11
Zodiacal Light 4:10 – 5:10 a.m. East
12
Zodiacal Light 4:12 – 5:12 a.m. East
13
Zodiacal Light 4:13 – 5:13 a.m. East
14
Zodiacal Light 4:14 – 5:14 a.m. East
15
Zodiacal Light 4:15 – 5:15 a.m. East
16
Zodiacal Light 4:16 – 5:16 a.m. East
17
Zodiacal Light 5:06 – 5:17 a.m. East
18 19 20
21 22 23 24 25 26 27
28 29 30

 December 2021
SUN MON TUE WED THU FRI SAT
1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31

The best nights to observe the zodiacal light at mid-northern latitudes occur when the ecliptic plane intersects the horizon at an angle of 60° or steeper. The dates above were chosen on that basis, with the Sun at least 18° below the horizon and the Moon below the horizon being used to calculate the times. An interval of time of one hour either before morning twilight or after evening twilight was chosen arbitrarily because it is the “best one hour” for observing the zodiacal light. The zodiacal light cone will be brightest and will reach highest above the horizon when the Sun is 18° below the horizon (astronomical twilight), but no less.

If you are interested in calculating the angle the ecliptic makes with your horizon for any date and time, you can use the following formula:

$\cos I = \cos \varepsilon \sin \phi-\sin \varepsilon \cos \phi \sin \theta$

where I is the angle between the ecliptic and the horizon, ε is  the obliquity of the ecliptic, φ is the latitude of the observer, and θ is the local sidereal time (the right ascension of objects on the observer's meridian at the time of observation).

Here’s a SAS program I wrote to do these calculations:

References
Meeus, J. Astronomical Algorithms. 2nd ed., Willmann-Bell, 1998, p. 99.

## Meteor Shower Calendar 2021

Here’s our meteor shower calendar for 2021.  It is sourced from the IMO’s Working List of Visual Meteor Showers (https://www.imo.net/files/meteor-shower/cal2021.pdf, Table 5, p. 25).

Each meteor shower is identified using its three-character IAU meteor shower code.  Codes are bold on the date of maximum, and one day either side of maximum.

Here’s a printable PDF file of the meteor shower calendar shown below:

Happy meteor watching!

 January 2021
SUN MON TUE WED THU FRI SAT
1
DLM QUA
2
DLM QUA
3
DLM QUA
4
DLM QUA
5
DLM QUA
6
DLM QUA
7
DLM QUA
8
DLM QUA
9
DLM QUA
10
DLM QUA GUM
11
DLM QUA GUM
12
DLM QUA GUM
13
DLM GUM
14
DLM GUM
15
DLM GUM
16
DLM GUM
17
DLM GUM
18
DLM GUM
19
DLM GUM
20
DLM GUM
21
DLM GUM
22
DLM GUM
23
DLM
24
DLM
25
DLM
26
DLM
27
DLM
28
DLM
29
DLM
30
DLM
31
DLM ACE

 February 2021
SUN MON TUE WED THU FRI SAT
1
DLM ACE
2
DLM ACE
3
DLM ACE
4
DLM ACE
5
ACE
6
ACE
7
ACE
8
ACE
9
ACE
10
ACE
11
ACE
12
ACE
13
ACE
14
ACE
15
ACE
16
ACE
17
ACE
18
ACE
19
ACE
20
ACE
21 22 23 24 25
GNO
26
GNO
27
GNO
28
GNO

 March 2021
SUN MON TUE WED THU FRI SAT
1
GNO
2
GNO
3
GNO
4
GNO
5
GNO
6
GNO
7
GNO
8
GNO
9
GNO
10
GNO
11
GNO
12
GNO
13
GNO
14
GNO
15
GNO
16
GNO
17
GNO
18
GNO
19
GNO
20
GNO
21
GNO
22
GNO
23
GNO
24
GNO
25
GNO
26
GNO
27
GNO
28
GNO
29 30 31
 April 2021
SUN MON TUE WED THU FRI SAT
1 2 3
4 5 6 7 8 9 10
11 12 13 14
LYR
15
PPU LYR
16
PPU LYR
17
PPU LYR
18
PPU LYR
19
ETA PPU LYR
20
ETA PPU LYR
21
ETA PPU LYR
22
ETA PPU LYR
23
ETA PPU LYR
24
ETA PPU LYR
25
ETA PPU LYR
26
ETA PPU LYR
27
ETA PPU LYR
28
ETA PPU LYR
29
ETA LYR
30
ETA LYR

 May 2021
SUN MON TUE WED THU FRI SAT
1
ETA
2
ETA
3
ELY ETA
4
ELY ETA
5
ELY ETA
6
ELY ETA
7
ELY ETA
8
ELY ETA
9
ELY ETA
10
ELY ETA
11
ELY ETA
12
ELY ETA
13
ELY ETA
14
ARI ELY ETA
15
ARI ETA
16
ARI ETA
17
ARI ETA
18
ARI ETA
19
ARI ETA
20
ARI ETA
21
ARI ETA
22
ARI ETA
23
ARI ETA
24
ARI ETA
25
ARI ETA
26
ARI ETA
27
ARI ETA
28
ARI ETA
29
ARI
30
ARI
31
ARI

 June 2021
SUN MON TUE WED THU FRI SAT
1
ARI
2
ARI
3
ARI
4
ARI
5
ARI
6
ARI
7
ARI
8
ARI
9
ARI
10
ARI
11
ARI
12
ARI
13
ARI
14
ARI
15
ARI
16
ARI
17
ARI
18
ARI
19
ARI
20
ARI
21
ARI
22
JBO ARI
23
JBO ARI
24
JBO ARI
25
JBO
26
JBO
27
JBO
28
JBO
29
JBO
30
JBO

 July 2021
SUN MON TUE WED THU FRI SAT
1
JBO
2
JBO
3
CAP
4
CAP
5
CAP
6
CAP
7
CAP
8
CAP
9
CAP
10
CAP
11
CAP
12
CAP SDA
13
CAP SDA
14
CAP SDA
15
CAP SDA PAU
16
CAP SDA PAU
17
PER CAP SDA PAU
18
PER CAP SDA PAU
19
PER CAP SDA PAU
20
PER CAP SDA PAU
21
PER CAP SDA PAU
22
PER CAP SDA PAU
23
PER CAP SDA PAU
24
PER CAP SDA PAU
25
PER CAP SDA PAU
26
PER CAP SDA PAU
27
PER CAP SDA PAU
28
PER CAP SDA PAU
29
PER CAP SDA PAU
30
PER CAP SDA PAU
31
PER CAP SDA PAU
 August 2021
SUN MON TUE WED THU FRI SAT
1
PER CAP SDA PAU
2
PER CAP SDA PAU
3
KCG PER CAP SDA PAU
4
KCG PER CAP SDA PAU
5
KCG PER CAP SDA PAU
6
KCG PER CAP SDA PAU
7
KCG PER CAP SDA PAU
8
KCG PER CAP SDA PAU
9
KCG PER CAP SDA PAU
10
KCG PER CAP SDA PAU
11
KCG PER CAP SDA
12
KCG PER CAP SDA
13
KCG PER CAP SDA
14
KCG PER CAP SDA
15
KCG PER CAP SDA
16
KCG PER SDA
17
KCG PER SDA
18
KCG PER SDA
19
KCG PER SDA
20
KCG PER SDA
21
KCG PER SDA
22
KCG PER SDA
23
KCG PER SDA
24
KCG PER
25
KCG
26 27 28
AUR
29
AUR
30
AUR
31
AUR

 September 2021
SUN MON TUE WED THU FRI SAT
1
AUR
2
AUR
3
AUR
4
AUR
5
SPE AUR
6
SPE
7
SPE
8
SPE
9
DSX SPE
10
STA DSX SPE
11
STA DSX SPE
12
STA DSX SPE
13
STA DSX SPE
14
STA DSX SPE
15
STA DSX SPE
16
STA DSX SPE
17
STA DSX SPE
18
STA DSX SPE
19
STA DSX SPE
20
STA DSX SPE
21
STA DSX SPE
22
STA DSX
23
STA DSX
24
STA DSX
25
STA DSX
26
STA DSX
27
STA DSX
28
STA DSX
29
STA DSX
30
STA DSX

 October 2021
SUN MON TUE WED THU FRI SAT
1
STA DSX
2
ORI STA DSX
3
ORI STA DSX
4
ORI STA OCT DSX
5
ORI STA OCT DSX
6
ORI STA DRA OCT DSX
7
ORI STA DRA DSX
8
ORI STA DRA DSX
9
ORI STA DRA DSX
10
ORI DAU STA DRA
11
ORI DAU STA
12
ORI DAU STA
13
ORI DAU STA
14
ORI EGE DAU STA
15
ORI EGE DAU STA
16
ORI EGE DAU STA
17
ORI EGE DAU STA
18
ORI EGE DAU STA
19
LMI ORI EGE STA
20
NTA LMI ORI EGE STA
21
NTA LMI ORI EGE STA
22
NTA LMI ORI EGE STA
23
NTA LMI ORI EGE STA
24
NTA LMI ORI EGE STA
25
NTA LMI ORI EGE STA
26
NTA LMI ORI EGE STA
27
NTA LMI ORI EGE STA
28
NTA ORI STA
29
NTA ORI STA
30
NTA ORI STA
31
NTA ORI STA

 November 2021
SUN MON TUE WED THU FRI SAT
1
NTA ORI STA
2
NTA ORI STA
3
NTA ORI STA
4
NTA ORI STA
5
NTA ORI STA
6
LEO NTA ORI STA
7
LEO NTA ORI STA
8
LEO NTA STA
9
LEO NTA STA
10
LEO NTA STA
11
LEO NTA STA
12
LEO NTA STA
13
NOO LEO NTA STA
14
NOO LEO NTA STA
15
NOO AMO LEO NTA STA
16
NOO AMO LEO NTA STA
17
NOO AMO LEO NTA STA
18
NOO AMO LEO NTA STA
19
NOO AMO LEO NTA STA
20
NOO AMO LEO NTA STA
21
NOO AMO LEO NTA
22
NOO AMO LEO NTA
23
NOO AMO LEO NTA
24
NOO AMO LEO NTA
25
NOO AMO LEO NTA
26
NOO LEO NTA
27
NOO LEO NTA
28
PHO NOO LEO NTA
29
PHO NOO LEO NTA
30
PHO NOO LEO NTA

 December 2021
SUN MON TUE WED THU FRI SAT
1
PUP PHO NOO NTA
2
PUP PHO NOO NTA
3
HYD PUP PHO NOO NTA
4
GEM HYD PUP PHO NOO NTA
5
DLM GEM HYD MON PUP PHO NOO NTA
6
DLM GEM HYD MON PUP PHO NOO NTA
7
DLM GEM HYD MON PUP PHO NTA
8
DLM GEM HYD MON PUP PHO NTA
9
DLM GEM HYD MON PUP PHO NTA
10
DLM GEM HYD MON PUP NTA
11
DLM GEM HYD MON PUP
12
DLM COM GEM HYD MON PUP
13
DLM COM GEM HYD MON PUP
14
DLM COM GEM HYD MON PUP
15
DLM COM GEM HYD MON PUP
16
DLM COM GEM HYD MON
17
DLM URS COM GEM HYD MON
18
DLM URS COM GEM HYD MON
19
DLM URS COM GEM HYD MON
20
DLM URS COM GEM HYD MON
21
DLM URS COM
22
DLM URS COM
23
DLM URS COM
24
DLM URS
25
DLM URS
26
DLM URS
27
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## Earliest Sunset, Latest Sunrise

Why does the Earliest Sunset come before the Winter Solstice and the Latest Sunrise after?

Why does the Earliest Sunrise come before the Summer Solstice and the Latest Sunset after?

Ever wonder? I have. And aside from some hand-wavy explanations, I’ve never been able to explain this very well. Here’s the best explanation I have seen yet, provided in the December 2007 issue of Sky & Telescope, p. 55:

You’d think the earliest sunset would come on the shortest day (or longest night) of the year, at the winter solstice. But in fact, the day-night cycle shifts back and forth a little with the seasons, due to the tilt of Earth’s axis and the ellipticity of Earth’s orbit. At the beginning of December, sunrise, midday, and sunset all happen a little earlier than they “should”, and in January they run a little late. So the earliest sunset ends up being two or three weeks before the solstice, and the latest sunrise is two or three weeks afterward. The exact dates depend on your latitude.

Continuing along that same line of thought…

At the beginning of June, sunrise, midday, and sunset all happen a little later than they “should” and in July they run a little earlier. So the earliest sunrise ends up being about a week before the solstice, and the latest sunset is about a week afterwards. The exact dates depend on your latitude.

I know, I know. You still have a question. “Why are the dates of earliest sunrise and latest sunset closer to the summer solstice than the dates of earliest sunset and latest sunrise to the winter solstice?” Good question. I think it has everything to do with the fact that the Earth is near aphelion at the time of the summer solstice, and thus moving most slowly in its orbit around the Sun (the Earth’s orbit is slightly elliptical and not circular). That means that the Sun is moving slowest against the background stars and thus the accumulated difference between the sidereal day and solar day is the smallest at that time of year. That means the spread of days between earliest sunrise and latest sunset is less. Conversely, at the winter solstice, Earth is near perihelion, and therefore it is moving most quickly in its orbit around the Sun. That means that the Sun is moving fastest against the background stars and thus the accumulated difference between the sidereal day and solar day is largest at that time of year. That means the spread of days between earliest sunset and latest sunrise is more.

Here in Dodgeville, Wisconsin, where the latitude is just shy of 43˚ N and the longitude is just a tad over 90˚ W, the earliest sunset this year is today, Tuesday, December 8, 2020, at 4:25:49 p.m.

Latest sunrise in 2021 will be on both Saturday, January 2 and Sunday, January 3 at 7:31:51 a.m.

Pause to consider that if we were on year-round daylight saving time, latest sunrise wouldn’t be until 8:31:51 a.m.

My preference would be to stay on standard time year-round, as Arizona does.

## Why Did It Take a Telescope to Discover the Orion Nebula?

Using the newly-invented telescope, French astronomer Nicolas-Claude Fabri de Peiresc (1580-1637) discovered the now-famous Orion Nebula (M42) when he was 29 years old, 410 years ago on this day.

November 26, 1610.

But wait a minute. You and I can see a nebulous “star” below the belt of Orion with our unaided eyes under a reasonably dark sky. Why wasn’t this object discovered long before the invention of the telescope?

Apparently, there is no known report of a “nebulous star” in the sword of Orion prior to Peiresc’s discovery. Is the Orion nebula brighter now than it was a few centuries ago? Is it possible an earlier observational report somehow got missed or was not properly interpreted?

There is speculation that the Maya civilization of Mesoamerica recognized the Orion Nebula long before Peiresc’s discovery, describing it as smoke from the smoldering embers of creation.

One can only stand in wonderment at the knowledge and experiences of hundreds of generations of men, women, and children who are utterly unknown to us today. Passed from person to person and generation to generation through oral tradition, never written down and eventually lost. Or written down on documents that later disintegrated or were purposefully destroyed.

Who hasn’t wished that they could could time travel back to the past? Have you ever wondered what your current location looked like a hundred years ago? A thousand years ago? Ten thousand or more years ago? Though sending humans into the past will probably never be possible, who’s to say that we won’t eventually figure out a way to view and perhaps even hear the past, without actually being there or having the ability to change it?

## John Brashear: A Man Who Loved the Stars

Pittsburgh telescope maker, optician, and educator John Alfred Brashear (1840-1920) was born 180 years ago this day. His world-renowned optical company made much of the astronomical equipment in use in the United States during the late 19th and early 20th centuries. His works included a 30-inch refractor for Allegheny Observatory in Pittsburgh, a 15-inch refractor for the Dominion Observatory in Canada, and the 8-inch refractor at the Drake University Municipal Observatory in Des Moines, Iowa.

My good friend, telescope maker Drew Sorenson in Jefferson, Iowa, has been a fan of John Brashear for many years. Not only does Drew make fine refractors as did Brashear, but there is more than a little resemblance between the two men. Drew introduced me to a delightful book entitled John A. Brashear: The Autobiography of A Man who Loved the Stars, which was first published posthumously in 1924. For anyone interested in the history of astronomy and the life of a scientist and humanitarian who struggled from near-obscurity to great success with only an elementary school education, this book is a must-read.

Here are three of my favorite passages from the book.

Somewhere beneath the stars is work which you alone were meant to do. Never rest until you have found it.

There is another yarn I cannot resist telling. The young farmer who had been bringing Mrs. Brashear her supply of vegetables asked her one day if I would let him look in the big telescope if he came up some clear evening. She encouraged him to do so, and I found him waiting one night to see the sights. I did not know whether or not he had any knowledge of astronomy, but I asked him what he would like to look at. He replied, “Juniper.” I told him that unfortunately that planet was not visible in the sky at the time. Then he expressed a desire to see “Satan.” But his Satanic Majesty was not around either. The climax came when he asked if I could show him the “Star of Jerusalem!” I ended it by showing him the moon and some clusters, and he went home very happy.

I remember, too, an old gentleman over eighty years of age who climbed the hill one moonlight night for a look in the telescope. The good man was utterly exhausted when he reached the house, and Ma and I had him lie down on the lounge to rest before climbing the stairs to the telescope. The views that night were fine, and I can hear the soliloquy yet of the dear fellow as he said, “For many years I have desired to see the beauties of the heavens in a telescope. I have read about them and heard lectures about them, but I never dreamed they were so beautiful.” We invited him to stay all night; but as it was moonlight, and much easier for him to go down the hill than to come up, he insisted on going home. I went part of the way with him to see that he got along all right; and all the way he expressed his delight at having the wish of a lifetime gratified that night.

Three weeks later the funeral cortège of that old man passed along the road on the opposite hillside that led to the cemetery, and it has always been a pleasure to remember that I was able to be of some service in gratifying one of his desires of a lifetime.

I think that all my life I have been partial to old people and children, and it has always been a source of genuine pleasure to contribute to their happiness.

John A. Brashear: The Autobiography of A Man who Loved the Stars (1924)

## Repurposing an Existing Community

One approach to establishing a dark-sky, astronomy-friendly, community is to find a small town in a rural area that would be receptive to doing the following:

1. Enact a comprehensive lighting ordinance that will be enforced
2. Eliminate all dusk-to-dawn outdoor lighting
3. Apply for International Dark Sky Community status

Obviously, this is going to be easier to do in a small community, and most likely one that is economically depressed.

What’s in it for them? What would the motivating factors be?

• A commitment from X number of people that they would move to the community provided the community agrees to 1-3 above being done. Options for new residents would be to either purchase or rent an existing home/apartment/RV space/etc., or to build the same but land would have to be available.
• The new residents would commit to working with the existing residents and businesses to improve the community and provide new opportunities, ensuring that this is a win-win situation for both existing and new residents.
• The new residents would commit to doing some or all of the things outlined in the Mirador Astronomy Village specifications document, or something like it.
• The influx of new residents and tourism will benefit all in the community, both economically and socially.

Does anyone know of a rural community that might be interested in putting their town “on the map” as an astronomy-friendly community for residents and visitors?

## First Photograph of the Orion Nebula

Henry Draper (1837-1882)

On this date 140 years ago, American physician and prominent amateur astronomer Henry Draper (1837-1882) made the first successful photograph of the Great Nebula in Orion, now usually referred to as the Orion Nebula. He used an 11-inch telescope (an Alvan Clark refractor!) and an exposure time of 50 minutes for the black and white photograph.

Draper continued to improve his technique, and a year and a half later he obtained a 137-minute exposure showing much more detail.

It really is amazing how image recording technology has improved over the past century and a half! At its best, film-based photography had a quantum efficiency of only about 2%, which means that only 2 out of every 100 photons of light impinging on the photographic medium is actually recorded. The rest is reflected or absorbed. The human eye—when well dark adapted—has a quantum efficiency of 15% or better, easily besting photography. Why, then, do photographs of deep sky objects show so much more detail than what can be seen through the eyepiece? The explanation is that the human eye can integrate photons and hold an image for only about 0.1 second. Film, on the other hand, can hold an image much longer. Even with reciprocity failure, photographic media like film can collect photons for minutes or even hours, giving them a big advantage over the human eye. But charge-coupled devices (CCDs) are a considerable improvement over older technologies since they typically have a quantum efficiency of 70% up to 90% or more. The CCD has truly revolutionized both professional and amateur astronomy in recent decades.