Astronomical targets

When to look at which interesting deep sky objects

Now that I have a telescope, I need to find something to look at in the sky. Saturn and Jupiter were pretty easy to find since they are so bright. Nevertheless, the first photos taken look ugly. I compiled a list of potentially interesting targets. Let’s see, if I can find and recognize them.

Some remarks to the following text


  • All terrestrial position related times in here are given for Mainz, Germany (50°N/8°E) if not mentioned otherwise.
  • The sun and moon tables are updated daily.
  • I sometimes write ‘stars’ as synonym for all objects also including galaxies and nebulas.

Astronomical coordinate system

This applies only to objects outside our solar system. Those in our solar system are to fast.

Coordinates of astronomical objects are mostly given in the equatorial coordinate system with the right ascension (RA) given in hours and the declination (dec) given in degree.

The equator is always at 0° declination, which means in Mainz (50°N) I can neglect everything with a declination close and less than -40° since those objects never cross the horizon and those with a declination larger than 50° will be visible the whole night. The 0h ascension “angle” is defined by the sun at the 21. March 12 GMT, more on the right ascension under Season.

Finding the right time

Weather

To see the stars there should be no clouds in the sky. One can look out the window, at a cloud forecasts/weather app on the smartphone or visit the webpage of your confidence, e.g.

Sunrise/-set and twilight

It should be dark, therefore late enough. After the sunset, when the sun disappeared behind the horizon, it is not immediately dark. It will be ‘totally’ dark after the astronomical twilight, which is when the sun is 18° below the horizon. Nevertheless, lay astronomers like me may start earlier in the evening or later in the morning.

Based on the sun’s angle relative to the horizon there are also a few other definitions/agreements.

  • astronomical twilight < 18° below horizon
  • nautical twitlight < 12° below horizon (not listed here)
  • blue hour 8° - 4° below horizon
  • civil twilight < 6° below horizon
  • golden hour 6° below and above horizon

This table here shows the times for the current day:

Moon

As long as I don’t want to see the moon, I should try to look at the stars before the moon rise, after moonset or the days at around new moon. At full moon the moon shines the whole night long, and with each following day the moon rises ~50 minutes later. Below is a figure with the moon rise, culmination, set moon phase and distance from earth in km for yesterday and the next 14 days.

Or use other ressources in the world wide web:

Season

Equally to the sun, the stars reach their highest position (culmination) over the horizon on the northern hemisphere in the south. And (like the sun on noon at midsummer) each star has once a year a maximum culmination. Not surprisingly this is contrary to the sun at midnight.

This maximum culmination can be estimated from the right ascension (RA, German: “Rektaszension”), which is given in hours. 0h is defined as the direction towards the sun on the 21. March 12:00 GMT. This means stars with a right ascension of ~12h reach their maximum culmination (at midnight) in spring, ~18h in summer, ~0h in autumn and ~6h in winter. If I want to see the star’s culmination before midnight, I must do that after the maximum culmination. If I want to see the culmination before the date of maximum culmination I either have to stay up very long or wake up very early.

List

I collected all the data from Wikipedia. Sometimes the coordinates there were given with several decimal places. I rounded them, since it does not make sense with several orders of magnitude between extent and the precision of the coordinates.

The further south the objects are and the less bright they are, it’s getting harder to spot them. The brightness is given as apparent magnitude (m): the lower the number the brighter they are. Polaris (marking the north pole) has an apparent magnitude of ~2, the sun of ~-26. The human eye has a limit around 4-7. For my 127mm telescope the limiting aperture is ~13.

I will extend the list below with the objects and give it a color code, with

Name Type RA dec m size
double stars
Mesarthim double star 1h 53m 32s 19° 17' 38" 4
Theta Tauri double star 4h 28m 34s 15° 57' 44" 4
Rigel double star 5h 14m 32s -8° 12' 6" 7
Alnitak double star 5h 40m 46' -1° 56' 34" 2
Porrima double star 12h 41m 40s -1° 26' 58" 3
Mizar and
Alcor
double star 13h 23m 55s
13h 25m 14s
54° 55' 31"
54° 59' 17"
4
2
Algieba double star 10h 19m 58s 19° 50' 29" 2
Epsilon Lyrae double star 18h 44m 20s 39° 40' 12" 5
Albireo double star 19h 30m 43s 27° 57' 35" 6
star cluster
NGC 869 + 884 double cluster 2h 19m 6s 57° 9' 4 30'
M 45 (Pleiades) open cluster 3h 47m 24s 24° 7' 2 110'
Hyades open cluster 4h 27m 15°52' 0.5 330'
NGC 1893 open cluster 5h 22m 44s 33° 24' 4" 8 11'
M 38 open cluster 5h 28m 43s 35° 51' 18" 7 21'
M 36 open cluster 5h 36m 18s 34° 8' 24" 6 10'
M 35 open cluster 6h 8m 54s 24° 20' 5 28'
NGC 2419 globular cluster 7h 38m 9s 38° 52' 55" 9 6'
M 44
(beehive)
open cluster 8h 40m 24s 19° 59' 4 95'
M 3 globular cluster 13h 42m 12s 28° 22' 38" 6 18'
M 4 globular cluster 16h 23m 35s 26° 31' 33" 6 26'
M 13 globular cluster 16h 41m 41s 36° 27' 35" 6 20'
M 6 (Butterfly) open cluster 17h 40m 6s -32° 13' 4.2 25'
M 92 globular cluster 17h 17m 7s 43° 8' 9" 6 14'
M 16 (Eagle) open cluster
+ nebula
18h 18m 48s -13° 49' 6 60'
M 22 globular cluster 18h 36m 24s -23° 54' 12" 5 32"
NGC 6633 open cluster 18h 27m 42s 6° 34' 5 27'
M 11 (Wild Duck) open cluster 18h 51m 5s -6° 16' 12" 6 23'
M 54 globular cluster 18h 55m 3s -30° 28' 48" 8 12'
M 15 globular cluster 21h 29m 59s 12° 10' 1" 6 18"
M 2 globular cluster 21h 33m 27s -0° 49' 24" 6 16"
galaxies
M 31
(Andromeda)
galaxy 0h 42m 44s 41° 16' 9" 3
NGC 253
(Sculptor)
galaxy 0h 47m 33s -25° 17' 18" 8 27'
M 33
(Triangulum)
galaxy 1h 33m 50s 30° 39' 36" 6 71'
M 81
(Bode's)
galaxy 9h 55m 33s 69° 3' 55" 7 20'
M 82
(Cigar)
galaxy 9h 55m 52s 69° 40' 47" 8 10'
M 51
(Whirlpool)
galaxy 13h 29m 53s 47° 11' 43" 8 11'
M 101
(pinwheel)
galaxy 14h 3m 13s 54° 20' 57" 8 28'
M 104
(Sombrero)
galaxy 12h 39m 59s -11° 37' 23" 8 9'
nebulas
NGC 281
(Pac-Man)
nebula 0h 52m 59s 56° 37' 19" 7 35'
M 76
(Little Dumbbell)
nebula 1h 42m 24s 51° 34' 31" 10 2'
NGC 896 (Heart) nebula 2h 33m 22s 61° 26' 36" 7 150'
IC 1848 (Soul) nebula 2h 55m 24s 60° 24' 36" 7 150'
NGC 1499
(California)
nebula 4h 3m 18s 36° 25' 18" 6 2.5°
IC 405
(Flaming star)
nebula 5h 16m 5s 34° 27' 49" 6 37'
M 42 (Orion) nebula 5h 35m 17s -5° 23' 28" 4 65'
NGC 2024 (Flame) nebula 5h 41m 54s -1° 51' 0" 10 30'
IC 434 nebula 5h 41m 1s -2° 27' 14" 11 60'
NGC 2174
(Monkey Head)
nebula 6h 9m 42s 20° 30' 7 40'
IC 443
(Jellyfish)
nebula 6h 17m 13s 22° 31' 5" 12 50'
NGC 2237
(Rosette)
nebula 6h 33m 45s 4° 59' 54" 9 5
NGC 2392
(Eskimo)
nebula 7h 29m 11s 20° 54' 42" 10 48"
M 97 (Owl) nebula 11h 14m 48s 55° 1' 9" 10 3'
NGC 6543
(Cat's Eye)
nebula 17h 58m 33s 66° 37' 59s 10 20"
M 20 (Trifid) nebula 18h 2m 23s -23° 1' 48" 6 28'
M 8 (Lagoon) nebula 18h 3m 37s -24° 23' 12" 6 90'
M 57 (Ring) nebula 18h 53m 35s 33° 1' 45" 9 4'
M 27 (Dumbbell) nebula 19h 59m 36s 22° 43' 16" 8 8'
NGC 6888
(Crescent)
nebula 20h 12m 7s 38° 21' 18" 7 18'
NGC 6960 (Veil) nebula 20h 45m 38s 30° 42' 30" 7
IC 1396
(elephant's trunk)
cluster + nebula 21h 38m 58s 59° 29' 18" 4 150'
NGC 7662
(Snowball)
nebula 23h 25m 54s 42° 32' 6" 9 37"

Although the Andromeda galaxy is visible with binoculars, the view through the telescope was a bit disappointing. The blurred spot of milk was just bigger. Maybe due to bad seeing or let’s see if I can train my eyes to see more details in the future.

Alcor is called “Reiterlein” in German because it is smaller and “rides” on Mizar.

Add-on 2021-11-07: Calculation of camera-sensor/lens parameters

To check, if a target fits on my camera sensor, I’ve created an extra page just with a table calculating the angle of view (AOV) and maximum exposure time for varying focal length and sensor layouts fitting on a smartphone screen.

References


See also