Tycho Galaxy is a face-on map of the Milky Way galaxy within about 700 pc (2300 ly) of the Sun. It is derived from the 1069480 stars that had relatively low error measurements (error/parallax < 0.2) in the Tycho-Gaia Astrometric Solution (TGAS) star parallax catalog.
Tycho Galaxy is one component of the Tycho Explorer, which also includes Tycho Sky, an overlay of the Tycho-2 star catalog in galactic coordinates on several infrared surveys.
The star colours are derived from the B - V colour index computed from data in the Tycho-2 catalog and the size is derived from the star's absolute magnitude.
To avoid an overwhelming amount of detail, only a few stars are shown at the top level and more stars are shown as you zoom in.
The stars are overlaid on a background taken from three sources:
The direction of the centre of the galaxy is towards the top of the map.
You can pan and zoom to any star in the map by entering an identifier in the search box at the upper right. Beneath the search box are two options:
At the upper left are controls to zoom in and out, return to the home view, expand to full screen mode, rotate the map clockwise and rotate the map counterclockwise. The rotation controls are provided because there is no strong consensus on the orientation of face-on maps of the Milky Way, so you can reorient the map so that the centre of the Milky Way is above, below, to the left or right.
You can also move left, right, up and down by dragging your mouse, using the arrow keys, or using the WASD keys. You can zoom in and out using the + and - keys or your mouse wheel.
Clicking or tapping will zoom into the current position. Double clicking/tapping will move the reticle (green cross) to the current location of the tap or mouse pointer.
At high zoom levels, hovering your mouse pointer over a star will show the name of the object and its distance above or below the galactic plane. Tapping or clicking will bring up a popup table with more information (including a link to Tycho Sky so that you can see the position of the star above or below the galactic plane).
Note that the parallax error given in the popup box does not include a possible systematic parallax error of up to 0.3 mas.
The galactic longitude and distance from the Sun along the galactic plane of the current mouse pointer location appear at the lower left.