April 10
The Paired Orbits
Sun Position
The Sun is in Aries near +13° declination. Northern hemisphere evenings are pleasant and long; southern hemisphere observers are well into autumn's earlier sunsets.
Sky Highlight
April 10 marks the anniversary of the first published image of a black hole's shadow, M87's central black hole, released on April 10, 2019, by the Event Horizon Telescope Collaboration. This is not an annually recurring sky event but is a fixed calendar landmark worth noting: M87 itself is well placed in the evening sky this week.
Deep Sky Object
M60 (NGC 4649), giant elliptical galaxy in Virgo, about 55 million light-years. M60 forms a visual pair with NGC 4647 and hosts one of the most massive black holes measured in a nearby galaxy, estimated at 4.5 billion solar masses; it interacts gravitationally with NGC 4647. Visible in small telescopes from both hemispheres.
Featured Star
Porrima (γ Vir) is a matched pair of F0V yellow-white main-sequence stars 38.1 light-years away, orbiting each other on a 169-year period with a notably elliptical orbit. The two stars are nearly identical twins in mass and temperature, making Porrima a textbook example of a physical binary whose orbital parameters have been pinned down with high precision.
Around This Date
- April 10, 2019The Event Horizon Telescope Collaboration released the first direct image of a black hole shadow, showing the 6.5-billion-solar-mass object at the center of galaxy M87.
- April 12, 1961Yuri Gagarin completed the first human spaceflight, orbiting Earth once aboard Vostok 1 and landing safely in the Soviet Union.
Porrima's two stars have been orbiting each other since before our Sun formed any planets; they are about halfway through one lap of their 169-year circuit.