The Moon – smaller than a thumb …


Again and again it is spoken about the Moon in the night sky, and the visible size for us here from Earth and we would like to recall some details or outline and summarize them again:

The Sun and the Moon about the same size in the sky
The full moon in the sky appears to have almost the same size as the Sun by day, because the Sun is approx. 400 times as large as the Moon, but also 400 times further away. So it balances itself out and this is how these two very different sized orbs appear to be of the same magnitude to us.

The Moon varies in distance and size
Due to the shape and the position of the Moon’s orbit around the Earth, the Moon gets closer to the Earth in some months during the year and hence appears to be slightly larger. The astronomical term for this is »perigee«. This is also popularly called »supermoon«, even though, this is slightly exaggerated, because the Moon is only 7% larger than on average. Is the Moon further away (»apogee«), it is up to 7% smaller than on average. This would be, so to speak, the »minimoon«.

The Moon appears larger on the horizon
In general, the Moon appears larger to us when it is within close proximity to the horizon (at moonrise or moonset). This optical illusion is called Moon illusion.

The Moon smaller than the thumb (»thumb rule«)
To switch off the Moon illusion, you can create a small frame with your hands around the Moon. Or you stretch your arm, hold up the thumb and cover the Moon with it. The Moon is then about half the size of the tip of your thumb, so it can always be covered by the thumb, regardless how large or small it was at the time. This »thumb rule« is often passed on incorrectly, if it claims that the Moon has the same size as the thumb. In reality, the Moon is only half the size. The thumb rule is shown in the movie »Dear John«, whereby here too, cheating was involved. The Moon is depicted too big in the movie!

It is interesting how the size of the Moon keeps people occupied on many levels. The reality is of course: the Moon has always the same size. Only for us it varies.


  1. Erin Mahoney | 2 November 2017

    I just love the full moon memo, I have sent it to my whole family everyone loves it. I just was curious is there any way that you could add mountain time in the United States? Though it be so appreciated let us know What you think you. we’re from denver area in Colorado. In this article rule of thumb, I’ve never heard it mentioned in conjunction with the moon. The rule of thumb for my understanding was that a man could never beat his wife with anything larger then his thumb. Hence the rule of thumb. This is a new one for me thanks for the education! 🙂

  2. Anonymous | 2 November 2017

    Liebes Ehepaar Werner!

    Vielen Dank für Euren Vollmondkalender und das wundervolle Engagement, das Ihr dafür aufwendet.
    Da Ihr am Starnberg und ich in Königsbrunn bei Augsburg wohne, finde ich es schade, dass mir sämtliche Artikel in Englisch zukommen, da ich nicht so gut Englisch – jedoch hervorragend Deutsch – spreche….

    Vielleicht ist es Euch ja möglich, mir zukünftig Eure “Vollmond-Post” in unserer Muttersprache zukommen zu lassen? Das wäre echt toll.

    Vielen herzlichen Dank und liebe Grüße aus Kö’brunn
    G. Lemcke / LichtinsDunkel37

  3. atlanta falcons gear | 14 April 2014

    good articles

  4. Anonymous | 20 January 2014

    Love the fullmoon pages.

Leave a Reply

Your email address will not be published. Required fields are marked *

Cookie Consent with Real Cookie Banner