Q&A of the Day

Chandra Operations Resume After Cause of Safe Mode Identified


At approximately 9:55 a.m. EDT on October 10, 2018, NASA’s Chandra X-ray Observatory entered Safe Mode, where the telescope’s instruments are put into a safe configuration, critical hardware is swapped to back-up units, the spacecraft points so that the solar panels get maximum sunlight, and the mirrors point away from the Sun. All systems functioned as expected and the scientific instruments are safe.

The cause of Chandra's safe mode on October 10 has been researched and the Operations team has successfully returned the spacecraft to its normal pointing mode. The safe mode was caused by a glitch in one of Chandra's gyroscopes resulting in a 3-second period of bad data that in turn led the on-board computer to calculate an incorrect value for the spacecraft momentum. The erroneous momentum indication then triggered the safe mode. The team has completed plans to switch gyroscopes and place the gyroscope that experienced the glitch in reserve. Once configured with a series of pre-tested flight software patches, the team will return Chandra to science operations which are expected to commence next week.

Below are some questions and answers with additional technical detail.

Q and A of the Day: Where did the name "Chandra" come from?

Q: Where did the name "Chandra" originate?

A: NASA's premier X-ray observatory was named the Chandra X-ray Observatory in honor of the late Indian-American Nobel laureate, Subrahmanyan Chandrasekhar (pronounced: su/bra/mon'/yon chandra/say/kar). Known to the world as Chandra (which means "moon" or "luminous" in Sanskrit), he was widely regarded as one of the foremost astrophysicists of the twentieth century.

Time, Gravity, and the Holiday Season


With the seeming time warp of the holiday season upon us, we decided to look up the answer to a question submitted by a Chandra visitor some time ago on the relationship of time and gravity. (Disclaimer: you may not use this text as an excuse to why you forgot to get your 'favorite' relative a gift this year. That's on you - not Einstein.)


Why is time influenced by gravity?

Einstein's theory of relativity showed that space and time are not independent. One consequence of this is that time can appear to pass more rapidly or slowly for two different observers depending on their relative velocities and acceleration. According to the theory of relativity, acceleration and gravity are equivalent, so gravity can affect the flow of time.

Q and A of the Day: How Have Telescopes Changed Things?

This set of queries came in from a couple of students, and we liked senior scientist Martin Elvis's responses so much that we thought we'd post them for everyone to see.

How do you feel the telescope has changed the scientific view on our universe?

Hugely! Before the telescope we thought the universe was big, but we really had no idea how big. Telescopes immediately showed us that there were vastly more stars out there than we had thought, but it took lots of work making bigger and better telescopes -- and learning how to use them. It took lots of work before we started to know how far away the stars were (using "parallax"), where we fit into the Milky Way, our galaxy (on the edge - dust in space hid our view so we thought we were in the middle), and the Milky Way into the scheme of all galaxies. It's a LONG story, and always our view widens, and is still widening. Now we can see back to when the galaxies were forming, but we have only just begun to find planets around other stars.

Q and A of the Day: White Dwarfs vs. Neutron Stars?

What are five differences between white dwarfs and neutron stars?
White Dwarfs
The major difference is due to the way in which they are formed.
1. White dwarfs are formed from the collapse of low mass stars, less than about 10 time the mass of the Sun. This star loses most of its mass in a wind, leaving behind a core that is less than 1.44 solar mass. On the other hand, neutron stars are formed in the catastrophic collapse of the core of a massive star.
Other differences follow:


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