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Cosmology Ruler Bookmark for Teaching and Outreach Purposes (Pen-and-pencil cosmological ruler calculator for everyone, especially students)

Cosmology in general, and relation between redshift and cosmic epoch in particular, is usually obscure to first years university students, secondary students, as well as journalists, politicians and the general public scientists may have interactions with. I identify the need for a simple artifact scientists may give to the public to clarify a few relations between redshift and other physical quantities, more meaningful for a non-scientist audience. This simple bookmark aims at completing previous "pen-and-pencil cosmological calculator" nomograms. I created a small, handy, duplicable bookmark with two printed sides, showing the corresponding cosmological values of redshift, age, time, and angular scale (for 1 kpc), using the Planck 2018 cosmology. On the recto, the redshift range of [0.1, 1000] approaches the recombination with a logarithmic scale. On the verso, the redshift range is chosen to be [0, 30] using a linear scale, covering the range of current (and future) detections of galaxies. A few examples are given, illustrating e.g. Planck, JWST or Euclid capabilities and complementarities, time interval non-linearity, properties of galaxies and clusters. This handy bookmark may be printed cheaply and offered to every student in physics (undergrad and grad student) in our universities or to secondary schools students we visit. The Cosmology Ruler Bookmark included is ready to print (single- or double-sided). The python script is available on github, allowing changes adapted to everyone's needs for teaching and outreach purposes, including with other cosmologies or applied to other scientific fields.