June 15
The Star That Proved We Move
Sun Position
The Sun is in Gemini, declination near +23.3°. Northern days are at their longest; the summer solstice is less than a week away.
Sky Highlight
No major meteor shower peaks today. This is an excellent week to observe the northern circumpolar sky: Draco coils high overhead from mid-northern latitudes, and the constellation's distinctive head quadrilateral is easily recognized near Hercules.
Deep Sky Object
M13 (Great Hercules Cluster), a globular cluster about 22,200 light-years away. M13 in Hercules is the showpiece globular cluster of the northern sky, containing several hundred thousand stars; in 1974, the Arecibo radio telescope beamed a binary-encoded message toward it, the famous Arecibo Message. Excellent from northern mid-latitudes through June and July evenings; binoculars show a fuzzy patch, a small telescope begins to resolve stars.
Featured Star
Etamin (γ Dra) is an orange giant (K5III) 148 light-years away in Draco; in 1728, James Bradley tracked its apparent position across the sky and found it shifted not because of parallax, but because Earth's orbital motion tilts the incoming angle of light, the discovery of stellar aberration. This proved Earth orbits the Sun from direct observation, independent of any model.
Around This Date
- June 15, 1999NASA launched the FUSE (Far Ultraviolet Spectroscopic Explorer) satellite, which studied the chemical composition of gas in the universe through far-ultraviolet spectroscopy.
- June 16, 1963Soviet cosmonaut Valentina Tereshkova became the first woman in space, orbiting Earth 48 times over nearly three days aboard Vostok 6.
The dragon's eye gave us proof that the ground beneath us moves, and astronomers have been grateful ever since.