Astronomical targets

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.

• Kachelmannwetter
• Clear Outside
• meteoblue: Weather
• meteoblue: Astronomy Seeing Widget:

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:

• sunrisesunset.de.
• timeanddate.com

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

• blue: seen with the naked eye
• green: seen with binoculars
• yellow: easily seen with the telescope
• orange: harder to find
• red: Hmm, did I really see it or was it my imagination

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

• 10 Himmelsobjekte für Einsteiger und Anfänger
• Die schönsten Deep-Sky-Objekte für Anfänger
• Astronomie-mainz.de: Deep-Sky
• Helligkeit & Größenklasse
• Limiting Magnitude Table
• Astrofotografie: Nebel
• Teleskop-ABC (Free-book from the telescope seller)
• The above times for the sun- and moonrise/-set and moonphases were calculated daily with the python package pyephem

See also

• First stacked astrofoto
• DIY Focus mask
• Sky Map
• Telescope
• Focus stack of a linden tree seed